DSpace at VNU: Ar-40-Ar-39 geochronology of the charnockites and granulites of the Kan Nack complex, Kon Tum Massif, Vietnam

Journal of Asian Earth Sciences 25 (2005) 653–677
www.elsevier.com/locate/jaes

40

Ar–39Ar geochronology of the charnockites and granulites
of the Kan Nack complex, Kon Tum Massif, Vietnam

Henri Maluskia,*, Claude Lepvrierb, Andre´ Leyreloupa, Vu Van Ticha,c, Phan Truong Thic
a

Laboratoire de Ge´ochronologie, UMR5567, CNRS-ISTEEM, Universite´ Montpellier 2, Place Euge`ne Bataillon 34095, Montpellier, France
b
Laboratoire de Tectonique, ESA 7072, Universite´ Pierre et Marie Curie, 4 Place Jussieu, 75230 Paris, France
c
National University of Vietnam, Hanoi, 334 Nguyen Trai Thanh Xuan, Hanoi, Vietnam
Received 24 March 2004; accepted 20 July 2004

Abstract
The Truong Son Belt forms the eastern rim of the Indochina Block in Southeast Asia. The age of the metamorphism, mainly along NW–SE
mylonitic shear zones that affects this belt, has been formerly determined at about 240–250 Ma. This age corresponds to the Indosinian
tectonometamorphic episode. The Kon Tum Massif, situated to the south of this belt, comprises high-temperature rocks, the Kan Nack
Complex, including charnockites and granulites. The main charnockitic outcrops, restricted to the Song Ba Valley, establish the intrusive
nature of these magmatic rocks within granulite facies material. Basic charnockitic rocks are mainly quartz enderbites to norites and
hornblende–pyroxene granulite facies rocks. The 40Ar–39Ar age of intrusion-cooling of charnockitic magmas is determined from primary
magmatic biotites at about 245 Ma. In the east of the Kan Nack Complex some granulite facies rocks exhibit relicts of primary granulite
facies parageneses, whereas others show evidence of overprinting by a retrogressive low-grade metamorphism. Ar–Ar dating confirm this
evolution, giving ages of 400 Ma for primary relict granulite facies phases and 260–270 Ma from the most retrogressed samples establishing
the youngest limit for the granulite facies metamorphism. Granulites intruded by charnockites in the Song Ba Valley yield ages of about
250 Ma, equivalent to the ages of the charnockites, and have evidently been completely reset by these high temperature intrusions. Therefore,
the Kan Nack Complex of the Kon Tum Massif is not an independent unit with respect to the Indosinian orogen, but represents the deepcrustal part of this belt.

q 2004 Elsevier Ltd. All rights reserved.
Keywords: Vietnam; Kon Tum; Granulite facies metamorphism; Charnockites; Indosinian; Ar–Ar geochronology

1. Introduction
The tectonic development of the Indochinese peninsula
was the result of two main orogenic events. As defined by
Fromaget (1941), the Indosinian orogeny occurred during a
major episode in Late Permian and Triassic times and was
the expression of the collision of several Gondwana-derived
continental terranes (Indosinia, Sibumasu and South China),
after narrowing and suturing of different branches of
Paleotethys (Metcalfe, 1996, 1999; Lepvrier et al., 1997).
During the Tertiary period the collision of India with
Eurasia induced the subsequent extrusion of Indochina, after
resorption of the correlative part of Neotethys.
* Corresponding author. Tel.: C33 467 14 45 68; fax: C33 467 14 36 46.
E-mail address: (H. Maluski).
1367-9120/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jseaes.2004.07.004

The geology of the territory of Vietnam, which forms the
eastern border of the peninsula, reflects this tectonic
evolution (Fig. 1). The Truong Son Belt (Annamitic
Cordillera of the former French geologists—Fromaget,
1941) in the north-central part of the country, was built by
the Indosinian movements. The Red River Fault Zone in
northern Vietnam was the site of important left-lateral
shearing, due to the lateral extrusion of the Indochina Block
during the Tertiary.
The Kon Tum Massif forms the south-central part of

Vietnam and is commonly regarded as an old, stable
Precambrian basement (Tien et al., 1989). Because of the
occurrence of metasedimentary and meta-igneous granulites
and charnockites, this block has classically been interpreted
as a fragment of Gondwana, equivalent in age to similar
facies rocks which are exposed in southern India and


654

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Fig. 1. Main geological units in Vietnam. Major metamorphic complexes; suture zones; main mylonitic fault zones.

Antarctica (Katz, 1993). Previous ages determined by the
U–Pb, Rb–Sr and K–Ar methods fall in the range
1650–1810 Ma (Thi, 1985; Hai, 1989). Unfortunately,
these results were published without sufficient

documentation and the data are imprecise or unreliable.
New results obtained on the high-grade rocks, using both
Ar–Ar and U–Pb methods, are coincident with the ages
of w250 Ma formerly obtained in the Truong Son Belt


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

to the north of the Kon Tum Massif (Lepvrier et al., 1997;
Maluski and Lepvrier, 1998; Maluski et al., 1999, 2000,
2002; Carter et al., 2001; Nagy et al., 2001; Nam et al.,

2001).
The aim of this study is to constrain the age of
the thermotectonic phase which has affected the Kon Tum
Massif. Up-to-now, radiometric results related to this massif
have been obtained along classical sections and easy-toreach outcrops, as for example the Song Ba Valley, and
without any reference to their petrology. In this work,
samples for dating were selected after careful petrological
analysis, in order to distinguish clearly primary minerals
which developed during high-grade conditions, from those
which reflect an overprint under lower-grade conditions.
This preliminary investigation of parageneses is essential
with regards to the interpretation of their ages. We thus
present an extensive geochronological study of the charnockitic and granulite facies material which forms the Kan
Nack Complex in the Kon Tum Massif, using the 40Ar–39Ar
radiometric method, with reference to results recently
obtained by the U–Pb method on identical samples. The
studied area extends roughly between 148 and 158 N latitude
(Fig. 1). The surrounding low- to-high-grade metasedimentary series (Ngoc Linh Complex—Tien, 1989) is not
included in this work. These rocks extend to the northwards
to the latitude of Tra Bong, and constitute a link with the
Truong Son terranes. The Paleozoic Dien Binh series, which
lies to the W, represents an independent and older unit
(Lepvrier et al., in press).

2. Geology of Northern-Central Vietnam
and Kon Tum Massif: an overview
2.1. Northern-Central Vietnam
The Truong Son Belt (Fig. 1) occupies North-central
Vietnam and Eastern Laos to the north of the Kon Tum
Massif. Various types of rocks comprise this mountain

range. Amphibolite facies quartzites, micaschists, para- and
ortho-gneisses, amphibolites and marbles are restricted to
relatively narrow NW- to W-trending shear zones, marked
by the development of mylonites and ultra-mylonites
(Lepvrier et al., 1997). The mylonitic foliation is very
steep in these zones, and bears a subhorizontal NW–SE
stretching lineation. Various, clear kinematic indicators
reveal a constant dextral shear. Following a similar trend,
along Song Ma and between Tamky and Phuoc Son (Fig. 1),
ultrabasic and basic rocks have been interpreted as the
remains of dismembered and metamorphosed ophiolites,
defining Paleotethyan or older suture zones. Whatever the
age of the suturing, the same dextral ductile strike-slip
movements affected the rocks in these suture zones (Fig. 1)
(Lepvrier et al., 1997).
The metamorphic rocks are unconformably overlain
locally, by undeformed Upper-Triassic detrital red beds.

655

This unconformity provides an upper age limit to the
thermotectonic event.
Many 40Ar–39Ar ages obtained from synkinematic
metamorphic minerals in different parts of the belt cluster
around 245–250 Ma (Maluski et al., 1995; Lepvrier et al.,
1997). This indicates that the Truong Son Range was mainly
developed during a Late Permian–Early Triassic thermotectonic event, which is also exhibited in the Song Chay
Massif in northern Vietnam (Maluski et al., 2001). Such a
tectonic and metamorphic climax is significantly older than
the classical Late Triassic (Neotriassic) pre-Norian Indosinian phase (Fromaget, 1941). This has been confirmed by

Late Permian U–Pb crystallization ages on zircons from
granites in north-central Vietnam (Nagy and Scha¨rer, 1999)
and on zircons from orthogneiss, on the western bank of the
Red River (Carter et al., 2001). Taking into account the
right-lateral shear movements marking the NW- to Wtrending zones, the Late Permian–Early Triassic event
likely results from oblique collision of Indochina with the
neighboring South China and Sibumasu blocks (Lepvrier et
al., 1997; Carter et al., 2001). More recent strike-slip or
normal brittle movements reactivated some of the Triassic
shear zones, principally during Neogene and even Quaternary times. In addition, Oligo-Miocene ductile extension
has deeply affected the Bu Khang massif within the Truong
Son Belt (Fig. 1) (Maluski and Lepvrier, 1998; Jolivet et al.,
1999). In the North of Vietnam, the Red River Fault Zone,
which represents a major Cenozoic sinistral shear zone
linked to the extrusion of the Indochina Block, has been
extensively studied and we refer to a full bibliography in
Leloup et al. (2001).
2.2. The Kon Tum Massif
The Kon Tum Massif in south-central Vietnam represents an uplifted block of metamorphic rocks, covered
partly by Mesozoic continental red beds or even directly
capped by Neogene to Quaternary lava flows (Lee et al.,
1998). To the West, in Cambodia, the Kon Tum Massif
probably extends beneath the Khorat Basin. A fission track
analysis indicates that the present-day topography is linked
to late Neogene crustal uplift associated with basaltic
eruptions (Carter et al., 2000).
In contrast to the Truong Son Belt where dominant
NW–SE to E–W tectonic directions are conspicuous
features, the Kon Tum Massif (Fig. 2), as shown in the
central and western portions, is controlled by N–S fractures

and shear zones. The central-eastern part of the Kon Tum
Block is occupied by the Kan Nack Complex (Tien et al.,
1989) formed by anatectic granulitic and charnockitic rocks.
These rocks are surrounded, sometimes in fault contact (Ba
To fault), by amphibolite facies gneisses and schists
belonging to the Ngoc Linh Formation (Tien et al., 1989)
that (to the N and W of the massif) consists principally of
biotite–hornblende gneisses, amphibolites, biotite–sillimanite–garnet–bearing schists, graphitic schists. As shown


656

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Fig. 2. Geological sketch map of the Kon Tum Massif: Precise GPS locations are given in Tables 2 and 5.

along the cross-section from Kon Tum city to Song Re´
River, through Konplong, these rocks form a wide antiform
that exhibits normal shear movements on both flanks, while
a large granitic Cretaceous undeformed body occupies the
core of the structure (Fig. 3.1).
Similarly, the granulitic rocks of the Kan Nack Complex
exposed along the upper course of the Song Ba River
(Fig. 2) are represented by Al-rich metapelites, quartzites
and marbles, have a foliation with a low to moderate dip,
locally mylonitic, and form gentle dome structures
(Fig. 3.2). Charnockitic bodies, represented by enderbites
(quartz–plagioclase–pyroxene high-grade magmatic rocks)
and locally norites (hypersthene clinopyroxene gabbros),
occur in the core of these structures. The structural

relationships between the charnockites and granulites has
been observed clearly at several sites and the intrusive
nature of the contact is now well established. Along the
Song Ba River, near Kan Nack, inclusions of foliated
granulites occur within the charnockites. Intrusive charnockitic lenses, although moderately deformed, exhibit
gneissic or banded structures in their outer parts and become
more massive in their centres.

The western part of the Kon Tum Massif is bounded by a
major N–S fault (Tri, 1986), which can be followed for at
least 100 km, from Phuoc Son along the Po Ko River; this is
named the “Po Ko Fault Zone” (Fig. 1). At the latitude of
Dak To, the Po Ko Fault swings eastwards and splays in
different branches towards the Sathay Valley and towards
the Kon Tum Basin and probably extends more to the south
beneath the Pleiku plateau basalts reaching the lower course
of the Song Ba. To the east of the fault recently discovered
charnockitic rocks are exposed, which constitute the
westernmost occurrence of these rocks. To the west, there
are mainly non-granulite facies meta-igneous rocks that
belong to an independent tectonic unit, known as the Dien
Binh Complex, which has older Paleozoic ages (Maluski
et al., 2002; Lepvrier et al, in press; Tich, 2004). The
foliated and sometimes mylonitic rocks, cropping out on
both sides of the structure, follow the strike of the fault and
display a constant N-trending and W-dipping steep to
moderate foliation, except in the Dak To segment, where the
foliation bends to WNW–ESE. When exposed, stretching
and mineral lineations are systematically WNW- to NWoriented. Late Indosinian movements along this fault are

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

657

Fig. 3. Two E–W cross-sections through the Kon Tum Massif (see location (1) and (2) on Fig. 2.1. Kan Nack Complex (granulite facies gneisses, quartzites,
metapelites, marbles intruded by charnockites (in black) and both invaded by migmatites (in grey); (2) Ngoc Linh Complex: orthogneisses, amphibolites,
micaschists (locally with S/C normal shear bands) invaded by migmatitic granites; (3) ophiolites (peridotites and pyroxenites in a sheared serpentinite matrix);
(4) Dien Binh Complex: Paleozoic ortho-granodiorites to diorites, surrounded by amphibolite facies metasedimentary foliated rocks; (5) non-foliated Mesozoic
granite and felsic rocks; (6) Permo-Triassic lavas and Upper Triassic terrigenous sediments; (7) Neogene sediments of the Kon Tum basin; (8) Quaternary
basalts. A,B,C,D refer to the samples location (Fig. 2).

dated at 232G2 Ma by synkinematic biotites sealed by late
undeformed granodioritic intrusions which were emplaced
at 204G1 Ma (Lepvrier et al., in press).
In the northern part of the Kon Tum Massif, which forms
the transition with the Truong Son Belt (Fig. 1), the E–W
dextral shear zones of Quang Ngai-Trabong and TamkyPhuoc Son progressively bend north-westwards to connect
with the Po Ko Fault (Fig. 1.2).

the north of Kan Nack town. (Fig. 2). This area lies on the
western rim of the Kan Nack Complex where enderbites and
two pyroxenes–plagioclase granulite facies rocks occur. In
addition, two further localities were visited (Fig. 2C,D) that
exhibit two pyroxene–hornblende and clinopyroxene–hornblende–plagioclase granulite facies rocks.
The different charnockitic rocks are described in Table 1
according to their mineralogy. A careful observation of thin
sections has enabled separation of primary and late
secondary parageneses:

3. The Kan Nack Complex
We present the main data related to parageneses found in
the charnockites and in the granulitic facies metamorphic
rocks. Then ages of both rock types are discussed in
conjunction with their metamorphic assemblages. Granulitic rocks, and to a lesser extent the charnockites, contain
complex assemblages developed during ambient P–T
conditions after the peak of metamorphism and during
overprinting in low-grade conditions. Consequently, the
interpretation of the isotopic ages depends of the attribution
of the parageneses to particular metamorphic conditions.
Petrological data were obtained after an extensive study
with Camebax 50 Microprobe (Service Commun Microsonde Sud, Montpellier, France). Ar–Ar methodology
applied in this work is described in Appendix.

3.1.1. Primary paragenesis
Whatever their location, the charnockitic rocks contain the
primary assemblage: plagioclase, clinopyroxene, Gorthopyroxene, Ggarnet, Gquartz, GTi-rich red biotite and Gcalcic
amphibole. In more basic samples, biotite and amphibole were
formed later than and surround the pyroxenes.
3.1.2. Late retrograde paragenesis
Some retrograde phases occur close to late microcracks.
Orthopyroxene has been transformed to cummingtonite and
magnesio-cummingtonite, brown hornblende to yellow
pistacite, and feldspars to secondary white micas. The
growth of these secondary minerals is linked to a retrogressive event, likely due to magma cooling and decompression during exhumation of the Kon Tum Massif.
40

Ar–39Ar geochronology of the charnockites

3.1. Mineralogy of charnockitic rocks

3.2.

The occurrence of charnockitic rocks is restricted to the
area along the upper course of the Song Ba River, to

Sixteen samples of charnockites have been dated in this
work; only two from the Song Ba Valley: VN522 from


658

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Table 1
Mineralogy of main charnockitic rocks
Rock type

Mineralogy

Quartz Enderbite
Without garnet
With garnet

Quartz, antiperthitic sodic plagioclase, hypersthene brown hornblende, green biotite
Quartz, antiperthitic sodic plagioclase (oligoclase/andesine), hypersthene, garnet (almandine-pyrope)
Red Ti-biotite
Minor: apatite, zircon, ilmenite, sphalerite

Norite

Without quartz
With quartz
Pyroxene-Amphibole Granulite Rock
Amphibole-Plagioclase Granulite
Rock

Andesine/labradorite, orthopyroxene (bronzite–hypersthene), amphibole
Quartz, andesine /labradorite, orthopyroxene, (bronzite/hypersthene) salitic clinopyroxene, red Ti-biotite,Gbrown
pargasitic amphibole Minor: apatite, zircon, ilmenite, magnetite,Gsphene
Labradorite, brown pargasitic hornblende, Ca-clinopyroxene, Gorthopyroxene, Gred Ti- biotite
Labradorite, brown pargasitic hornblende Ca-clinopyroxene, orthopyroxene, Gred Ti-biotite Minor: apatite,
zircon, Gsphene

the Bu Nu Brook in the western part of the Kan Nack
complex (Fig. 2D), and VN389 from the Dak To area,
outside the Kan Nack Complex to the west (Fig. 2C). All
other samples were collected along the upper course of the
Song Ba River (B, in Fig. 2).
A summary of the 40Ar–39Ar ages of biotites from the
charnockites and their respective GPS locations is given in
Table 2.
3.2.1. Song Ba River
Samples VN 810, 294, 358, 796, 812, 814, 799, 357, 798,
800, 813, 808, 364. (Between 14816 0 55 00 N; 108829 0 43 00 E
and 14808 0 18 00 N; 108835 0 15 00 E): Nearly all types of
charnockite are represented in these outcrops: norites,
quartz-two pyroxene–plagioclase granulite facies rocks
and quartz–enderbites. The biotite ages of these charnockitic rocks yield very comparable results (Fig. 4a–m): each
sample defines a flat plateau age which clusters between 238

and 245 Ma, except for sample VN364, which yields an
older age of 251.5G2.7 Ma. Only VN294, VN358, VN800
and VN364 (Fig. 4b,c,j,m) present significantly younger
ages in low to intermediate temperatures, due to argon loss
from less retentive domains and consequently diffusion
prior to the primary closure of the mineral. VN 294, 358 and
800 commonly show a slight alteration of biotites and
orthopyroxenes that are partly transformed to green chlorite,
and very tiny secondary white micas. Also, VN358 has
secondary carbonates in the matrix. This minor alteration
may explain the trend of age spectra related to the low
temperature steps (7–10% of 39Ar) rather than a late thermal
episode at w100–150 Ma. Nevertheless, this alteration was
not strong enough to disturb the more retentive sites, as
indicated by the plateau ages. The biotite of sample VN357
(Fig. 4 h) was analysed as a population and gives a complex
age spectrum for which a plateau age can be calculated only
between 1050 8C and the fusion temperature, corresponding

Table 2
Location and summary of ages of dated charnockites
Charnockites
Song BA River
VN810
VN294
VN358
VN796
VN812
VN814
VN799

VN357
VN798
VN800
VN813
VN808
VN364
SW SONG BA
VN295
BU NU BROOK
VN522
DAK TO
VN389

GPS position (N latitude; E longitude)

Rocks

AGE (Ma) BiZBiotite

14813 0 08 00 ; 108831 0 12 00
14808 0 16 00 ; 108836 0 06 00
14820 0 07 00 ; 108844 0 16 00
14816 0 55 00 ;108829 0 43 00
14808 0 18 00 ;108835 0 16 00
14807 0 51 00 ; 108833 0 40 00
14808 0 18 00 ;1088 00 35 0 15 00
14815 0 45 00 ; 108830 0 17 00
14808 0 18 00 ; 108835 0 15 00
14808 0 18 00 ; 108835 0 15 00
14808 0 18 00 ; 108835 0 15 00

14808 0 18 00 ; 108835 0 15 00
14814 0 18 00 ; 108830 0 21 00

Norite
Enderbite
Proxene-pl-norite
Quartz Enderbite
Norite
Pyroxene-pl-Norite
Quartz Enderbite
Quartz Enderbite
Quartz Pyroxene-pl
Quartz Enderbite
Pyroxene-pl
Pyroxene-pl
Quartz Enderbite

237.9G2.3 Bi
238.5G3.2 Bi
240.2G4.7 Bi
240.7G2.3 Bi
242.0G2.8 Bi
242.2G2.8 Bi
243.0G2.5 Bi
243.3G2.4 Bi
243.1G2.4 Bi
245.2G2.7 Bi
245.4G2.4 Bi
245.6G2.4 Bi
251.5G2.7 Bi

13858 0 44 00 ; 108831 0 38 00

Quartz Pyroxene-pl

226.5G3.6 Bi

14816 0 05 00 ; 108851 0 01 00

Amphibole-pl

264.3G3.2 Bi

14843 0 03 00 ; 108849 0 12 00

Quartz Enderbite

259.5G4.8 Bi


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

to w50% of released 39Ar at 243.3G2.4 Ma. A secondary
amphibole has developed in this sample at the expense of
the pyroxene.
VN364, which is a quartz enderbite, yields the oldest
plateau age at 251.5G2.7 Ma. Concerning its mineralogy,
this sample is a unique charnockite containing garnet in
equilibrium with orthopyroxene and Ti-rich biotite.

659

Sample VN295 (13858 0 44 00 N; 108831 0 38 00 E): This basic
charnockite, belongs to the Kan Nack Complex, but is
located SW of the Song Ba River (Fig. 2). The biotite yields a
plateau age at 226.5G3.6 Ma (Fig. 5) with a slight Ar
depletion in low temperature steps, giving younger ages at
w110–150 Ma, probably without any thermotectonic meaning. The plateau age is younger than that of previous samples.

Fig. 4. Age spectra of charnockites from the Song Ba River.


660

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Fig. 4 (continued)

3.2.2. NW Dak To
Sample VN389 (14843 0 03 00 N; 108849 0 12 00 E): Orthopyroxene-free enderbites to clinopyroxene–amphibole–plagioclase
granulite facies rocks occur within the metamorphic series of
the Ngoc Linh Formation, to the North of Dak To town. The
dated sample is an enderbite with a brown pargasitic
hornblende, salitic clinopyroxene and red Ti-rich biotite. A
secondary paragenesis in this rock is represented by chlorite,
actinolite and sphene, developed at the expense of amphiboles
and Ti-biotites. Biotites, which constitute an equilibrium
phase, give an age of 259.5G4.8 Ma (Fig. 6b), obtained on a
plateau fraction corresponding to 80% of released 39Ar,
clearly older than the average age of charnockites from

the Song Ba Valley. Low temperature increments yield
younger ages between 40 and 187 Ma, with a step at 164 Ma,
related to 12% of 39Ar released. This trend may be related to

Fig. 5. Age spectrum of the charnockite VN295, Dak To, SW of the Kan
Nack complex.


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

661

Fig. 6. Age spectra of charnockites from Bu Nu Brook (VN522) and Dak To (VN389).

the secondary paragenesis described above and in this case
would not be related to a precise thermotectonic event.
3.2.3. Bu Nu Brook
Sample VN522 (14816 0 05 00 ; 108851 0 01 00 ): Along the Bu
Nu Brook, these rocks are associated with amphibolites and
quartzites. They are diopside–augite–amphibole–plagioclase granulite facies rocks. Much brown hornblende has
developed after the pyroxene. The biotite yields a plateau
age of 264.3G3.2 Ma (Fig. 6a), without indication of argon
loss on low temperature steps, nor any evidence of an excess
Argon component. This result constitutes the oldest age we
have found in the charnockitic suite.
3.3. Mineral assemblages of the metasedimentary
granulite facies gneisses
3.3.1. The primordial granulite facies evolution
We have observed granulites along the Song Bien Brook,
south of Hoai An town, in the eastern part of the Kan Nack

Complex. They are also very well exposed along the upper
course of the Song Ba River where they occur in close
relationship to the charnockitic rocks (Fig. 2) and

constitute the basement of the Kan Nack Complex. To
the south, garnet–cordierite and cordierite–spinel assemblages linked to the peak of the granulite facies
metamorphism are well preserved, while to the north,
granulites experienced polymetamorphic conditions and
now exhibit only various relict granulite facies assemblages (Table 3). The protoliths of the granulites were
sedimentary Al-rich rocks including pelites, semi-pelites,
sandstones and Al-quartzites intercalated with calcareous
and dolomitic sediments. The more siliceous granulite
facies rocks are khondalitic and kinzigitic banded gneisses,
granulite facies metaquartzites, and scarce calcareousdolomitic rocks are represented by forsterite–humite–
clinopyroxene calc-silicates.
The high-grade metapelitic rocks are foliated, strongly
layered, and were deformed under ductile conditions. This is
demonstrated by a strong stretching lineation that contains
elongated prismatic sillimanite, quartz ribbons and oval
garnets in the main mylonitic shear zones, similar to those
described by Ji and Martignole (1994).
In metapelites muscovite is absent and has been replaced
by prismatic sillimanite and K-feldspar. K-feldspar is
generally mesoperthitic and sodic plagioclase is locally

Table 3
Primary paragenesis in granulites
Sample

Location

0

00

0

00

Rock type

Mineralogy
qtz, pl.ap, Ksp.mp, Ti-bi, grt, sill.p, crd, zr, graph, rt, chl2, pn2,
mus2
qtz, pl.ap, Ksp, bi, sill.p, grt, spl, zr, ap
qtz, pl, Ksp.mp, bi, grt, sill.p, crd, spl, dsp2, pn2
qtz, Ksp.mp, Ti-bi, grt, crd, white mica, chl2
qtz, pl.ap, Ksp, crd, Ti-bi, grt, pn2, sc2, chl2
qtz, grt, spl, pl, zr, ap, mus2, chl2
qtz, chld, mus, grt, chl, sill.p,
qtz, pl.ap, Ksp.mp, bi, sill.p, grt, spl, rt, Fe–Ti ox, chl, mus
qtz, pl.ap, Ksp.mp, Ti-bi, grt, sill.p, crd, spl, chl2, mus2, pn2, dsp2
qtz, pl.ap, Ksp.mp, Ti-bi, grt, crd, spl, chl2, mus2, pn2, dsp2
qtz, pl.ap, Ti-bi, grt, zr, ap, chl2

VN413

14818 04 N, 108829 01 E

Pelitic granulite

VN414
VN415
VN514
VN515
VN505
VN512
VN362
VN363
VN805
VN811

14818 0 04 00 N, 108829 0 01 00 E
14818 0 04 00 N, 108829 0 01 00 E
14818 0 04 00 N, 108829 0 01 00 E
14818 0 04 00 N, 108829 0 01 00 E
14815 0 04 00 N, 108850 0 32 00 E
14815 0 04 00 N, 108850 0 32 00 E
14813 0 47 00 N, 108830 0 53 00 E
14813 0 47 00 N, 108830 0 53 00 E
14813 0 47 00 N, 108830 0 53 00 E
14812 0 07 00 N, 108832 0 04 00 E

Granulite facies quartzite
Pelitic granulite
Anatectic granulite facies gneiss
Granulite facies gneiss
Quartz micaschist
Quartz micaschist
Quartzo-feldspathic granulite
Metatectic granulite

Semi-pelitic granulite
Granulite facies quartzite

List of abbreviations: Qtz, quartz; pl.ap, antiperthitic plagioclase; Ksp.mp, mesoperthitic K-feldspar; Ti-bi, Ti–Biotite; grt, garnet; sill.p, prismatic sillimanite;
crd, cordierite; zr, zircon; graph, graphite; rt, rutile; chl, chlorite; pn, pinite; mus, muscovite; spl, spinel; ap, apatite; dsp, diaspore; sc, sericite; ox, Fe–Ti oxides;
(2) refers to secondary paragenesis.


662

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

antiperthitic. Frequently, garnet coexists in equilibrium with
Mg-rich cordierite and cordierite with Fe-rich spinel. All
these observations indicate that granulite facies was
reached.
The compositional layers in the outcrops contain
different parageneses, for instance garnet–biotite–sillimanite–spinel, cordierite–biotite–sillimanite, and garnet, cordierite, biotite, sillimanite, cordierite, spinel in others. These
banded granulites suffered local anatexis, giving rise to
quartz, sodic plagioclase, K-feldspar, biotite, and sometimes
garnet in granulite facies leucosomes. Anatectic conditions
were reached within the stable biotite/quartz and garnet/
K-feldspar/sillimanite/Zn–Fe rich spinel stability fields.
Orthopyroxene is lacking in these leucosomes. In some
places, sillimanite and biotite, and garnet and sillimanite
have reacted together, giving rise respectively to garnet–
cordierite and cordierite–spinel coronas, which constitute
the stable critical parageneses during the granulite facies
metamorphic peak.
3.3.2. Late retrograde paragenesis: the low-to mediumgrade overprinting

All the pelitic and semipelitic granulite facies rocks
have experienced minor, heterogeneous, low- to mediumgrade retrogression according to their location in the Kan
Nack Complex. The less retrogressed samples are always
located in the Song Bien Brook and along the Song Ba
River (Fig. 2). The most retrograded samples are located
on the eastern rim of the block (Kim Son area, Fig. 2).
The low-grade alteration firstly begins along microfractures or by the way of shear zones and progressively
invades the granulite facies coronas, and then the whole
rocks. The main retrogressive phases are listed in the
Table 4.
This retrogressive process results in damouritization
(a variety of muscovite) of plagioclase, and transformation
of K-feldspar to white micas. The garnet is only partially
chloritized, whereas biotite has been completely altered.
The cordierite has been transformed to pinite, and then to
white mica. Locally, diaspore replaces spinel in the
cordierite–spinel reaction coronas. Late chloritoid,

Table 4
Mineralogy of retrogressive phases in the granulites
Granulites

Mineralogy of low-grade overprint

VN413
VN514
VN515
VN505
VN512
VN362

VN363
VN805
VN811

mus2, pinite,chl
white micas, chl
pinite, sericite, chl
mus replaces feldspar, chl in grt
white micas, chl, ctd
ctd, mus
chl, mu, pinite, dsp
mus, pinite, chl
Chl

ctd, Chloritoid; Other abbreviations same as for Table 3.

muscovite sensu stricto and chlorite may also nucleate
from the older granulite facies minerals of which only
prismatic sillimanite and garnet have survived.
This late nucleation strongly suggests a new low- to
medium- grade metamorphic overprint that is especially
well marked in the Kim Son region (Fig. 2), where only
granulite facies garnet and prismatic sillimanite have
survived in the new metamorphic assemblage, generally
as inclusions in Fe-chloritoid. Granulite facies biotites
have been totally transformed to chlorite and rutile
needles.
Locally, the coronas appear more or less deformed by
a younger tectono-metamorphic event. First, forming a
prominent ellipsoidal-shaped fabric. Late chloritoid,

muscovite, chlorite and exceptionally diaspore may also
nucleate on the older granulite facies minerals such as
biotite, garnet, cordierite, prismatic sillimanite, K-feldspar and spinels, and partially replace them along
cleavages or microcracks; this suggests H20 circulation.
This process seems to have affected mostly the northeastern margin of the Kan Nack Complex. We attribute this
to polymetamorphism rather than to simple cooling linked
to exhumation, as found in the Song Ba Valley and Song
Bien Brook, taking into account the huge size of the
neoblasts (e.g. chloritoid 1 cm long) that define the rough
new foliation.
We present results of 40Ar–39Ar analysis from eleven
samples of biotites and secondary muscovites from the
granulite facies gneisses according to their geographic
provenance. Ages and locations of samples are given in
Table 5.
The pressure conditions of this late retromorphic event
cannot be precisely estimated: diaspore and quartz are
not in textural equilibrium, which rules out high-pressure
conditions (Theye et al., 1997). Garnet is no longer in
equilibrium with plagioclase, thus no thermobarometric
calculation is possible. Because secondary white mica is
muscovite sensu stricto without phengite substitution, the
pressure regime is likely to have been low.
3.4. 40Ar–39Ar radiometric data of metasedimentary
granulite facies gneisses
3.4.1. Song Bien and Nuoc Dang Brook
Samples VN413, VN414, VN415, VN514, VN515
(14814 0 25 00 N; 108855 0 30 00 E): All these samples were
collected along a cross-section, following the Song Bien
Brook, over a distance of approximately 1 km. They are

situated on the eastern rim of the Kan Nack Complex (A in
Fig. 2). No charnockitic intrusions have been found in this
area. VN414 and VN415 are metasedimentary granulites,
like VN413. VN514, VN515 are ribonned granulite facies
paragneisses; age spectra obtained from their biotites have a
similar trend and present a flat plateau age, related to more
than 50% of 39Ar released, and are between 304 and
405 Ma. (Fig. 7a–e).


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

663

Table 5
Location and ages of biotites and muscovites from granulites
Metapelitic granulite facies rocks

GPS position
0

00

0

00

Rock type

Ar–Ar age (Ma) (Mineral)

VN413
VN414
VN415
VN514
VN515

14818 04 N, 108829 01 E
14818 0 04 00 N, 108829 0 01 00 E
14818 0 04 00 N, 108829 0 01 00 E
14818 0 04 00 N, 108829 0 01 00 E
14818 0 04 00 N, 108829 0 01 00 E

pelitic granulite
quartzitic granulite
Pelitic granulite
Granulite facies anatectic gneiss
Granulite facies gneiss

325.6G3.1 Bi
405.7G3.8 Bi
403.4G3.8 Bi
304.2G3.6 Bi
343.3G4.2 Bi

VN505
VN512
VN362
VN363
VN805

VN811

14815 0 04 00 N; 108850 0 32 00 E
14815 0 04 00 N; 108850 0 32 00 E
14813 0 47 00 N; 108830 0 53 00 E
14813 0 47 00 N; 108830 0 53 00 E
14813 0 47 00 N; 108830 0 53 00 E
14812 0 07 00 N, 108832 0 04 00 E

quartz micaschist
quartz micaschist
quartzo-feldspathic granulite
metatectic granulite
semi-pelitic granulite
quartzitic granulite

262.7G3.2 Mus
270.7G2.5 Mus
241.1G2.4 Bi
244.8G2.4 Bi
243.6G2.4 Bi
247.8G2.4 Bi

Bi for Biotite; Mus for Muscovite.

Fig. 7. Age spectra of granulites from the Song Bien Brook. VN414 and VN415 contain the most preserved granulite facies assemblages.


664

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Samples VN505, VN512 (14815 0 04 00 ; 108850 0 32 00 ):
VN505 and 512 were collected along the Nuoc Dang
Brook (A, in Fig. 2). Both are micaschists with relict
prismatic sillimanite and secondary muscovite. They yield
plateau ages of 262.7G3.2 and 270.7G2.5 Ma, respectively, for 40% and 80% of released Ar (Fig. 8a,b).
Concerning muscovite from VN 505 muscovite, most of
the radiogenic argon was released during the third step, due
to the high transparency of this mineral, which influences
dissipation of the laser beam energy. The age related to this
step is slightly older than the plateau age at 269G1 Ma. The
trend of these spectra does not present any Ar loss, and is
interpreted as reflecting the age of the closure of the system.
3.4.2. Granulitic gneisses from the Song Ba River
Samples VN362, VN363, VN805, VN811 (14813 0 47 00 ;
108830 0 53 00 ): These samples were collected along the
Song Ba River, to the north of Kan Nack town (B in Fig.
2) in an area where charnockites intrude the granulitic
gneisses. Well-defined plateaux ages were obtained for
these four biotites, for 50–90% of 39Ar released with
ages clustered between 241.1G2.4 and 247.8G2.4 Ma
(Fig. 9a–d). VN363 and VN 811 (Fig. 9b,d) present a
peculiar trend with slight Ar diffusion affecting the low
temperature steps, resulting in non-representative ages
(Table 6).

4. Interpretation and conclusions
4.1. Charnockites
Plateaux ages obtained from the biotites in the charnockites are reported in Fig. 11. Samples are plotted according to

their geographical location.
4.1.1. Song Ba River Group
The magmatic rocks, which represent the charnockitic
suite, are intrusive, as said above, into the granulite facies

metamorphic series. This observation is confirmed by
radiometric data obtained on primary matrix Ti-rich biotites
from the charnockites, the ages of which span 238 and
245 Ma (Fig. 10). These ages, which are younger than those
obtained for granulites from the Song Bien Group, probably
mark the youngest age limit for the intrusions of charnockite, or at least, the time when different charnockitic
intrusions formed as a closed system after cooling. The
retrogressive event responsible for the development of
chlorite, actinolitic amphibole, pistacite and secondary
carbonates and a more intense CO2-rich fluid circulation
may be responsible for the slight argon loss, which affected
the less retentive sites in some samples (e.g. VN294,
VN358, VN800, VN364 and VN389). The time interval,
between 238 and 245 Ma determined in this work is
confirmed by two independent U–Pb results (Nagy et al.,
2001) previously obtained on zircons from the same sample,
VN357, the biotite of which gives an Ar–Ar age of 243G
2 Ma. Five zircon fractions gave concordant dates, while
two fractions were slightly discordant. The average age
obtained was 249G2 Ma. With the SHRIMP technique,
Carter et al. (2001) obtained an age of 258G6 Ma, related to
the rims and cores of zircons, although there was some
evidence of late stage resorption. The close agreement of
these ages confirms the rapid cooling of these intrusions.
The local occurrence of foliated charnockites demonstrates that some magmas began to be emplaced during

Indosinian tectonic activity.
Among samples dated in the Song Ba Valley, only
VN364, which is the unique garnet-bearing enderbite, yields
an older plateau age of 251.1G2.7 Ma for the primary
biotites. Despite the position of this sample, closely
interbedded with other younger intrusions, this age could
correspond to an earlier phase of magmatic activity, and
thus reflects an intrusion/cooling Ar–Ar age. There is no
evidence for interpreting this age as the result of an excess
argon component.
Special attention must be paid to the coronitic norite VN
295 that outcrops in the extreme SW of the Song Ba Valley.

Fig. 8. Age spectra of granulites from the Song Bien brook overprinted by low-to medium grade metamorphism.


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

665

Fig. 9. Age spectra of granulites from the Song Ba River.

Its biotite age of 226.5G3.6 Ma represents the youngest age
obtained from the charnockites. Coronas are formed of
vermicular orthopyroxene–plagioclase symplectites, which
could be interpreted in terms of a decompression reaction
due to adiabatic uplift, or to a locally enhanced erosion rate.
Moreover, this sample shows a late overprint with
development of tiny secondary white micas. This late
development under different and new P–T conditions may

account for the younger age of the biotite. In this case, we
can assume the age is related to the final phase of Indosinian
thermotectonism.
4.1.2. Dak To and Bu Nu areas
Sample VN389 from the Dak To area is situated in the
westernmost outcrop of the studied charnockitic rocks in the
Kon Tum Massif (C in Fig. 2). It is separated from the Kan
Nack Complex by the Ngoc Linh Metamorphic Series. The
age yielded by Ti-rich biotites is 259.5G4.8 Ma, and is
therefore clearly older than the age of charnockites from the
Song Ba River. This result may correspond, as for the biotite
of VN364, to the age of earlier intrusion-cooling of these
charnockites. The thermal conditions occurring during the
development of a secondary paragenesis can be invoked to
explain the trend of younger ages in low extraction

temperatures. The same situation concerns charnockitic
rock VN522 (D in Fig. 2) that displays the same petrological
features as VN389 and is the only sample with a
charnockitic affinity found in the Bu Nu area, in the
easternmost part of the Kan Nack Complex. It is slightly
altered (chlorite after biotite) and does not contain
orthopyroxene. The age of 264.3G3.2 Ma obtained on
biotite may indicate, as for VN 389, that the intrusions of
charnockites were initiated some 20 Ma earlier than the
main intrusions in Song Ba, or may represent a differential
uplift between the rim and the core of the massif.
For these last two samples of biotite, as for biotite
VN364, we have no evidence to attribute this older age to an
excess Ar component

4.2. Metasedimentary granulites
All ages obtained on granulites are reported in Fig. 11.
Results cover a large interval between 405.7G3.8 and
244.2G2.7 Ma. Three age groups can be distinguished,
corresponding to three distinct areas: (a) the Song Bien
Brook (VN 414, VN415, VN413, VN514, VN515), related
to the oldest ages, (b) to the west of this area along the Nuoc
Dang Brook (VN505, VN512), and (c) along the Song Ba


666

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Table 6
Isotopic data for Ar–Ar analyses 40Ar* is radiogenic Argon

VN505 MUSCOVITE
Laser

VN512 MUSCOVITE
Laser

Sample
VN362 BIOTITE
Laser

VN363 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

1
2
3

40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

1
2
3
4
5
6
7
8
9
10

8.848
7.569
9.038
9.060
8.890
8.848
8.748
8.840
8.835
9.133

!1000
JZ.017734
2.505
1.942
0.196
0.025

0.045
0.040
0.070
0.044
0.134
0.012

0.029
0.056
0.104
0.109
0.110
0.111
0.111
0.111
0.108
0.109

0.222
0.103
0.000
0.001
0.000
0.000
0.009
0.000
0.003
0.000

0.0

74.0
1.0
57.3
6.5
5.8
59.5
0.7
63.4
1.3
80.8
1.1
84.0
2.0
93.1
1.3
94.1
3.9
100.0
0.3
Total ageZ266.4G3.3 Ma

262.9G49
227.2G5.5
268.2G9.5
268.8G1.2
264.1G2.0
262.9G1.1
260.2G4.0
262.7G1.5
262.6G6.3

270.8G1.3

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

8.243
9.942
9.273
9.549
9.403
9.128
9.113
8.979
9.062

9.336
9.186
9.329
9.467
9.200
9.106
9.436
9.204
9.087

JZ.017672
0.829
0.282
0.250
0.220
0.067
0.032
0.005
0.023
0.061
0.002
0.003
0.030
0.025
0.029
0.082
0.005
0.003
0.071

0.0915
0.0921
0.0998
0.0979
0.1042
0.1084
0.1095
0.1105
0.1083
0.1070
0.1087
0.1062
0.1048
0.1077
0.1071
0.1058
0.1085
0.1077

0.119
0.032
0.110
0.018
0.010
0.006
0.002
0.009
0.001
0.049
0.000

0.001
0.013
0.000
0.000
0.000
0.000
0.000

0.1
24.5
0.9
8.3
1.8
7.3
6.4
6.5
19.0
2.0
27.6
0.9
43.0
0.1
51.6
0.7
54.2
1.8
55.6
0.1
57.4
0.1

61.2
0.9
64.9
0.7
91.8
0.8
93.8
2.4
95.6
0.1
97.4
0.1
100.0
2.1
Total ageZ272.3G3.0 Ma

245.3G64
292.0G12
273.8G2.6
281.3G2.7
277.3G1.1
269.8G1.1
269.4G1.4
265.7G1.6
268.0G1.7
275.5G2.4
271.4G1.5
275.3G1.0
279.1G1.8
271.8G1.1

269.2G4.2
278.2G1.5
271.9G1.5
268.7G0.4

40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

% Atm

Age (Ma)

!1000
JZ.017791
4.449
7.217
8.412
7.893
7.869
7.985
7.991
8.011
8.006

8.034
8.222
7.967
7.975
8.113
7.955
8.101
7.959
!1000

1.181
0.651
0.446
0.147
0.166
0.082
0.096
0.065
0.075
0.052
0.030
0.061
0.104
0.069
0.092
0.091
0.071

0.146
0.111

0.103
0.121
0.120
0.121
0.121
0.122
0.122
0.122
0.120
0.123
0.121
0.120
0.122
0.120
0.123

–
0.053
0.054
0.036
0.047
0.052
0.064
0.140
0.039
0.022
0.016
0.010
0.014
0.008

0.005
0.000
0.006

0.2
0.1
2.5
8.2
11.0
19.1
25.0
30.3
39.7
47.3
60.0
74.4
77.4
81.9
84.0
87.0
100.0

34.9
19.2
13.1
4.3
34.9
2.4
2.9
1.9

2.2
1.6
0.9
1.8
3.1
2.1
2.7
2.7
2.1

137.4G15.5
217.9G7.6
251.6G4.8
237.0G1.8
236.4G1.4
239.6G1.7
239.8G2.6
240.3G2.2
240.2G2.8
241.0G1.7
246.3G3.4
239.1G1.2
239.3G2.7
243.2G2.9
238.8G2.6
242.9G2.6
238.9G0.9

1.609
0.948

1.129

0.121
0.088
0.137

0.233
0.040
0.170

0.2
0.7
1.3

47.5
28.0
33.3

133.44G47
243.22G14
149.45G16
(continued on next page)

JZ.017791
4.315
8.112
4.854

% Atm.

AGE G1sd


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

667

Table 6 (continued)
Sample
4
5
6
7
8
9
10
11
12
13
14
15
16
17
VN805 BIOTITE
Laser

VN811 BIOTITE
Laser

VN413 BIOTITE

Laser

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

1
2
3
4
5
6
7
8
9
10
11

12
13
14
15

1
2
3
4
5
6
7

40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

% Atm

Age (Ma)

4.673
6.682
8.241

8.309
8.077
8.199
8.258
8.410
8.228
8.084
8.146
8.071
8.028
8.146
!1000

1.895
0.888
0.141
0.024
0.084
0.030
0.047
0.009
0.043
0.061
0.041
0.031
0.084
0.052

0.094
0.110

0.116
0.119
0.120
0.120
0.119
0.118
0.119
0.121
0.121
0.122
0.121
0.120

0.328
0.091
0.001
0.010
0.012
0.015
0.013
0.011
0.010
0.004
0.009
0.003
0.015
0.001

1.5
3.1

6.1
10.0
15.3
20.4
28.0
35.9
45.1
57.7
61.0
74.4
77.5
100.0

56.0
26.2
4.1
0.7
2.4
0.8
1.4
0.2
1.2
1.8
1.2
0.9
2.5
1.5

144.1G42
202.66G6.0

246.82G3.7
248.73G2.7
242.24G1.8
245.67G2.0
247.31G2.6
251.57G3.5
246.47G1.4
242.42G2.4
244.17G3.1
242.07G1.7
240.88G3.9
244.18G1.8

0.460
0.081
0.035
0.049
0.085
0.140
0.099
0.046
0.036
0.036
0.042
0.029
0.001
0.024
0.020
0.073

0.114
0.129
0.124
0.130
0.127
0.122
0.119
0.121
0.121
0.121
0.120
0.123
0.125
0.124
0.123
0.126

0.012
0.012
0.016
0.015
0.021
0.002
0.025
0.017
0.021
0.025
0.009
0.003
0.008

0.008
0.001
0.005

2.1
8.4
14.6
23.4
27.9
31.8
37.1
43.6
50.8
58.5
65.6
74.1
78.2
81.4
86.8
100.0

13.6
2.4
1.0
1.4
2.5
4.1
2.9
1.3
1.0

1.0
1.2
0.8
0.0
0.7
0.6
2.1

226.7G2.5
227.1G1.5
239.8G1.3
228.5G4.0
231.7G1.7
235.9G1.6
244.7G2.1
243.6G3.4
245.6G1.3
244.6G1.2
246.7G3.4
241.3G1.9
240.4G1.0
241G2.7
242.2G2.3
232.9G2.5

JZ.017791
2.136
2.497
6.199
8.119

8.235
8.247
8.259
8.355
8.346
8.183
8.112
8.216
8.031
8.381
8.049

2.408
1.899
0.29
0.045
0.045
0.048
0.042
0.048
0.024
0.012
0.108
0.013
0.035
0.003
0.052

0.135
0.176

0.147
0.121
0.120
0.120
0.120
0.118
0.119
0.122
0.119
0.121
0.123
0.119
0.122

0.000
0.022
0.180
0.011
0.047
0.043
0.070
0.091
0.116
0.044
0.101
0.082
0.006
0.319
0.430

0.5
1.2
6.3
25.6
37.0
46.7
58.2
67.8
76.3
79.2
80.6
86.5
89.7
90.4
99.9

71.1
56.1
8.6
1.3
1.3
1.4
1.2
1.4
0.7
0.3
3.2
0.3
1.0
0.1

1.5

67.2G4.0
78.4G17
188.7G1.7
243.4G1.2
243.4G1.4
243.4G1.3
243.4G1.2
243.4G1.6
243.4G0.9
243.4G2.2
243.5G6.9
243.5G1.5
243.5G2.4
243.5G2.3
243.5G2.2

40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

!1000
JZ.017791
3.848
9.756

9.334
11.281
10.622
10.976
11.079

1.416
0.775
0.495
0.011
0.213
0.085
0.061

0.151
0.079
0.091
0.088
0.088
0.089
0.089

0.410
0.216
0.133
0.000
0.000
0.000
0.000

JZ.017791
7.528
7.542
7.993
7.591
7.703
7.852
8.167
8.128
8.197
8.162
8.238
8.044
8.013
8.034
8.077
7.746
!1000

% 39Ar

0.6
1.5
3.3
7.1
11.3
26.2
42.5

% Atm.

41.8
22.9
14.6
0.3
6.3
2.5
1.8

AGEG1sd

119.5G22
288.8G15
277.2G32
330.0G3.3
312.3G2.8
321.8G1.7
324.6G1.4
(continued on next page)


668

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Table 6 (continued)

8
9
10

11
12
13
14
15

40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

% 39Ar

% Atm.

AGEG1sd

11.197
11.225
11.067
11.057
11.027
10.951
11.096
11.679

0.074

0.088
0.057
0.055
0.066
0.131
0.306
0.065

0.087
0.087
0.089
0.089
0.089
0.088
0.082
0.084

0.000
0.000
0.000
0.029
0.012
0.028
0.168
0.058

60.7
2.1
67.5
2.6

74.8
1.7
79.6
1.6
89.4
1.9
95.8
3.8
96.8
9.0
100.0
1.9
Total ageZ325.6G3.1 Ma

327.7G1.3
328.5G2.4
324.3G2.6
324.0G2.6
323.2G1.8
321.2G3.8
325.0G13
340.6G3.8

1.273
0.780
0.243
0.128
0.040
0.064
0.043

0.045
0.051
0.112
0.056
0.034
0.169
0.167
0.012

0.077
0.064
0.039
0.070
0.071
0.069
0.070
0.070
0.070
0.068
0.068
0.069
0.073
0.073
0.072

0.001
0.040
0.011
0.011
0.011

0.001
0.085
0.000
0.000
0.000
0.007
0.002
0.031
0.000
0.028

0.3
37.6
1.0
23.0
4.8
7.2
8.6
3.8
17.4
1.1
42.6
1.9
51.4
1.2
60.0
1.3
68.8
1.5
72.4

3.3
78.3
1.6
94.3
1.0
95.4
5.0
97.5
4.9
99.9
0.3
Total ageZ411.9G3.8 Ma

243.8G18
351.4G11
634.8G3.5
397.1G3.3
397.6G6.2
404.3G2.4
405.7G2.9
401.6G2.0
404.8G1.7
408.0G5.7
410.6G4.3
408.2G2.9
375.9G6.0
377.4G3.4
395.8G2.3

2.902

2.833
0.114
0.044
0.106
0.059
0.094
0.049
0.106
0.068
0.048
0.136
0.008
0.048
0.138
0.186

0.100
0.074
0.071
0.073
0.068
0.069
0.069
0.070
0.069
0.070
0.070
0.069
0.069
0.071

0.069
0.067

0.455
0.886
0.002
0.001
0.000
0.010
0.125
0.000
0.000
0.000
0.005
0.014
0.008
0.005
0.030
0.040

0.3
85.7
0.4
83.7
11.0
3.3
31.2
1.3
35.2
3.1

42.8
1.7
49.2
2.8
58.0
1.4
63.4
3.1
75.1
2.0
78.7
1.4
81.5
4.0
85.9
2.3
95.3
1.4
98.1
4.0
99.9
5.5
Total ageZ397.6G3.8 Ma

44.9G25
69.2G58
390.0G2.6
389.0G5.1
405.1G6.0
405.6G2.4

404.3G3.8
405.0G3.2
404.5G3.9
403.0G1.9
402.0G4.9
399.1G4.9
406.6G5.9
399.9G3.0
398.4G5.8
404.7G11

0.199
0.045
0.027
0.035
0.021
0.023
0.033
0.033
0.022
0.017
0.007
0.002
0.111

0.091
0.095
0.095
0.094
0.093

0.094
0.097
0.096
0.097
0.096
0.095
0.094
0.090

0.004
0.011
0.002
0.000
0.025
0.017
0.007
0.000
0.000
0.014
0.000
2.090
0.020

13.5
30.2
38.5
44.4
54.3
63.8
71.4

79.4
89.5
93.4
96.5
99.3
100.0

!1000
VN414 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

JZ.017791
8.133
12.087

23.707
13.840
13.860
14.120
14.174
14.014
14.141
14.266
14.366
14.272
13.022
13.079
13.791
!1000

VN415 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10
11
12

13
14
15
16

JZ.017791
1.417
2.200
13.565
13.527
14.151
14.170
14.122
14.148
14.128
14.071
14.032
13.918
14.212
13.949
13.889
14.137
!1000

VN514 BIOTITE
Laser

1
2
3

4
5
6
7
8
9
10
11
12
13

JZ.017734
10.274
10.31
10.428
10.474
10.61
10.486
10.138
10.222
10.221
10.356
10.485
10.616
10.715

5.9
1.3
0.8
1.0

0.6
0.7
0.9
0.9
0.6
0.5
0.2
0.2
3.3

302.0G1.5
303.0G1.4
306.1G1.3
307.4G1.1
311.0G2.0
307.7G1.6
298.3G2.2
300.6G1.9
300.5G1.7
304.2G1.9
307.7G2.7
311.2G2.5
313.9G6.1
(continued on next page)


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

669

Table 6 (continued)
40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

% 39Ar

% Atm.

AGEG1sd

Total ageZ304.3 G3.6 Ma
!1000
VN515 BIOTITE
Laser

JZ.017734
11.860
11.999
11.541
11.740
12.174
11.533
11.005

0.161

0.012
0.032
0.077
0.039
0.202
0.127

40Ar*/39Ar

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

%Atm Ar

Age(Ma)G2 s

1
2
3
4
5
6
7
8
9

10
11
12
13
14
15

!1000
JZ.022995
4.086
3.504
3.208
5.235
5.676
5.820
5.823
5.810
5.731
5.650
5.682
5.323
5.858
5.801
6.032

0.582
0.182
0.420
0.262
0.110

0.073
0.040
0.036
0.034
0.073
0.090
0.067
0.036
0.052
0.065

0.202
0.270
0.272
0.176
0.170
0.168
0.169
0.170
0.172
0.173
0.171
0.184
0.168
0.169
0.162

0.410
0.356
0.382

0.129
0.051
0.028
0.017
0.024
0.033
0.127
0.150
0.130
0.101
0.159
0.196

0.2
17.2
0.7
5.3
2.9
12.4
5.7
7.7
9.9
3.2
19.6
2.1
33.8
1.1
41.9
1.0
47.7

1.0
52.1
2.1
57.3
2.6
64.4
2.0
68.3
1.0
89.1
1.5
99.9
1.9
Total ageZ221.8G3.5 Ma

162.0G52.0
139.8G28
128.4G6.8
205.0G5.4
221.3G3.3
226.6G1.6
226.7G1.1
226.2G1.7
223.3G3.0
220.3G3.7
221.5G2.7
208.3G2.1
228.0G3.8
225.9G0.9
234.3G1.5

1
2
3
4
5
6
7
8
9
10
11
12
13

JZ.017791
4.780
7.945
7.956
7.800
8.064
7.932
7.932
7.895
7.665
7.668
7.849
7.962
7.972

1.474
0.164
0.143
0.18
0.045
0.111
0.111
0.065
0.195
0.174
0.117
0.004
0.063

0.118
0.119
0.120
0.121
0.122
0.121
0.121
0.124
0.122
0.123
0.122
0.125
0.120

0.160
0.000

0.005
0.004
0.014
0.026
0.026
0.041
0.091
0.000
0.000
0.000
0.000

0.8
43.5
8.2
4.8
17.5
4.2
30.2
5.3
41.2
1.3
48.2
3.2
55.2
3.2
59.2
1.9
61.2
5.7

65.3
5.1
68.8
3.4
71.9
0.1
100.0
1.8
Total ageZ237.2G2.3 Ma

147.2G23.1
238.5G2.7
238.8G2.1
234.4G1.9
241.8G2.0
238.1G2.6
238.1G2.6
237.1G1.4
230.6G4.1
230.7G8.3
235.8G2.7
239.1G2.8
239.3G1.2

1
2
3
4
5
6

7
8
9
10

JZ.0228
4.157
3.457
4.681
6.198
6.236
6.314
6.225
6.026
5.953
6.063

1.456
0.836
0.507
0.141
0.047
0.059
0.045
0.170
0.128
0.113

0.137
0.217

0.181
0.154
0.158
0.155
0.158
0.157
0.161
0.159

0.092
0.125
0.049
0.008
0.002
0.007
0.023
0.032
0.055
0.063

1
2
3
4
5
6
7

Sample
VN295 BIOTITE

Population

0.080
0.082
0.085
0.083
0.081
0.081
0.087

0.000
0.000
0.002
0.046
0.014
0.260
0.013

37.5
4.7
66.0
0.3
88.6
0.9
92.4
2.2
97.3
1.1
98.3
5.9

100.0
3.7
Total ageZ343.3G4.1 Ma

344.4G1.7
348.0G1.6
335.9G2.3
341.2G5.1
352.6G2.5
352.6G2.6
352.6G2.7

!1000
VN810 BIOTITE
Laser

!1000
VN294 BIOTITE
Population

0.9
2.2
6.9
22.4
54.6
68.8
74.1
78.3
82.0
87.3

43.0
24.7
15.0
4.1
1.4
1.7
1.3
5.0
3.7
3.3

163.3G18.4
136.8G13.3
182.9G3.4
238.4G1.6
239.8G0.9
242.6G1.1
239.4G2.9
232.2G3.8
229.6G4.4
233.6G3.0
(continued on next page)


670

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Table 6 (continued)

Sample

40Ar*/39Ar
11
12
13
14

6.129
6.186
6.209
4.794

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

%Atm Ar

Age(Ma)G2 s

0.108
0.084
0.135
0.745

0.158
0.157
0.154
0.162

0.060
0.076
0.193
0.754

92.5
3.1
96.7
2.4
99.3
4.0
100
22.0
Total ageZ233.6G12 Ma

236.0G3.2
238.0G4.4
238.8G6.1
187.1G24.7

1.274
0.416
0.088
0.026
0.010

0.009
0.003
0.001
0.002
0.006

0.211
0.171
0.148
0.149
0.149
0.148
0.144
0.129
0.141
0.146

0.335
0.130
0.035
0.029
0.000
0.036
0.133
0.115
0.079
0.184

2.4
37.6

9.1
12.3
16.9
2.6
35.7
0.7
63.7
0.3
73.3
0.2
76.8
0.1
80.7
0.0
95.8
0.1
99.9
0.1
Total ageZ233.6G12 Ma

110.3G22.7
187.6G9.4
237.4G6.7
239.0G3.9
240.8G1.9
242.7G1.2
248.0G.9
276.1G2.1
254.1G3.5
244.7G11.9

2.35
0.994
0.288
0.073
0.000
0.053
0.063
0.061
0.139
0.043
0.051
0.065
0.001
0.011
0.003

0.050
0.093
0.119
0.122
0.121
0.119
0.121
0.122
0.120
0.122
0.123
0.121
0.127

0.116
0.121

0.011
0.052
0.027
0.028
0.025
0.033
0.035
0.032
0.018
0.007
0.011
0.014
0.058
0.000
0.052

0.1
69.4
0.3
29.3
2.5
8.5
10.3
2.1
21.3
0.0
29.9

1.5
37.0
1.8
43.4
1.8
48.4
4.1
60.2
1.2
72.7
1.5
83.4
1.9
86.0
0.0
87.0
0.3
99.9
0.10
Total ageZ242.0G2.3 Ma

184.3G200
227.5G40
229.8G3.6
239.1G1.2
245.7G1.6
245.7G2.1
241.6G1.1
240.2G1.5
238.7G1.6

241.0G1.3
239.6G1.3
242.5G1.0
236.3G1.7
255.2G1.9
246.0G1.1

2.532
1.033
1.844
1.019
0.941
0.678
0.511
0.075
0.114
0.034
0.094
0.148
0.469
0.746

0.133
0.102
0.066
0.091
0.088
0.098
0.104
0.120

0.119
0.121
0.119
0.116
0.112
0.100

0.246
0.032
0.023
0.012
0.000
0.006
0.011
0.014
0.021
0.019
0.002
0.010
0.097
0.037

1.1
74.8
3.3
30.5
8.2
54.5
16.7
30.1

24.4
27.8
32.2
20.0
39.8
15.1
53.3
2.2
62.6
3.3
75.1
1.0
84.7
2.7
89.3
4.4
91.7
13.8
100.0
22.0
Total age Z238.1G2.6 Ma

59.9G14
207.2G7.6
209.9G4.6
230.7G2.7
245.1G2.9
245.0G2.8
245.8G2.3
244.7G1.0

244.3G1.1
245.6G1.3
244.9G1.8
247.5G2.5
231.7G5.6
234.0G3.5

0.194
0.049
0.103
0.132
0.079
0.056

0.118
0.118
0.116
0.119
0.121
0.122

0.000
0.012
0.000
0.000
0.000
0.001

!1000
VN358 BIOTITE

Population

1
2
3
4
5
6
7
8
9
10

JZ.021358
2.954
5.130
6.584
6.634
6.687
6.743
6.901
7.745
7.081
6.802
!1000

VN796 BIOTITE
Laser

1

2
3
4
5
6
7
8
9
10
11
12
13
14
15.00

JZ.017791
6.048
7.557
7.636
7.966
8.203
8.202
8.056
8.006
7.954
8.035
7.985
8.089
7.869
8.544

8.214
!1000

VN800 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10
11
12
13
14

JZ.017832
1.894
6.827
6.921
7.650
8.162
8.158
8.188
8.146

8.135
8.181
8.153
8.247
7.688
7.768
!1000

VN812 BIOTITE
Laser

1
2
3
4
5
6

JZ.017791
7.981
8.341
8.354
8.045
8.062
8.071

5.4
17.9
26.5
34.9

42.1
49.8

5.7
1.4
3.0
3.9
2.3
1.6

239.5G3.7
249.6G1.9
250.0G1.5
241.3G3.5
241.8G2.5
242.0G3.0
(continued on next page)


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

671

Table 6 (continued)
Sample

40Ar*/39Ar
7
8
9

10
11

8.048
8.188
7.689
8.116
8.209

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

%Atm Ar

Age(Ma)G2 s

0.060
0.031
0.062
0.041
0.022

0.122
0.121
0.128

0.122
0.121

0.020
0.032
0.044
0.000
0.000

54.1
2.0
56.8
0.9
68.2
1.8
73.1
1.2
100.0
0.6
Total ageZ243.4G2.6 Ma

241.4G4.4
245.3G5.9
231.3G8.5
243.3G2.8
245.9G2.5

0.044
0.063
0.007

0.367
0.043
0.000
0.113
0.125
0.085
0.015
0.005
0.050
0.451

0.063
0.113
0.117
0.117
0.121
0.125
0.119
0.119
0.120
0.123
0.123
0.147
0.115

1.608
0.063
0.072
0.068
0.040

0.050
0.044
0.000
0.036
0.000
0.000
0.010
0.084

0.5
1.3
4.6
1.8
10.3
0.2
17.6
10.8
33.3
1.2
50.2
0.1
58.3
3.3
70.2
3.7
83.4
2.5
87.6
0.4
96.9

0.1
98.6
1.5
100.0
13.3
Total ageZ242.6G2.7 Ma

438.5G25
257.6G7.4
254.2G1.9
229.0G5.7
244.1G4.2
239.5G4.5
242.4G5.3
242.0G3.6
242.31G2.4
241.5G2.8
242.5G4.0
202.3G5.8
225.5G33

2.462
0.294
0.256
0.082
0.114
0.122
0.155
0.167
0.366

0.112
0.176

0.071
0.116
0.120
0.123
0.118
0.119
0.118
0.116
0.110
0.117
0.117

0.200
0.036
0.021
0.020
0.004
0.018
0.000
0.047
0.038
0.084
0.014

2.3
72.7
9.6

8.7
20
7.5
30.9
2.4
44.4
3.3
55.2
3.6
63.2
4.5
69.2
4.9
74.5
10.8
79.1
3.3
100.0
5.2
Total ageZ237.7G2.5 Ma

117.2G10
236.8G3.2
230.3G7.1
237.8G3.8
244.1G3.0
242.5G2.0
241.2G2.9
244.9G3.5
241.3G3.8

246.2G9.9
242.2G1.4

1.99
1.241
0.279
0.108
0.058
0.091
0.007
0.149
0.021
0.097
0.057
0.152

0.06
0.366
0.117
0.125
0.126
0.125
0.122
0.110
0.115
0.122
0.126
0.122

0.328

0.25
0.022
0.008
0.008
0.016
0.034
0.129
0.071
0.074
0.02
0.033

0.1
58.8
2.7
36.6
8.2
8.2
19.2
3.1
31.4
1.7
36.3
2.6
39.3
0.2
43.3
4.4
46.7
0.6

61.5
2.8
93
1.7
99.9
4.5
Total age Z238.7G2.4 Ma

213.2G150
56.2G9.7
242.2G4.0
237.9G2.1
241.1G2.0
239.4G5.5
250.7G7.1
264.7G5.6
264.2G6.2
245.4G1.6
240.8G.8.0
240.3G3.2

3.192
1.165
0.061
0.048
0.130
0.098
0.124

0.113

0.097
0.120
0.121
0.122
0.121
0.120

0.004
0.000
0.000
0.000
0.010
0.055
0.049

!1000
VN814 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10
11

12
13

JZ.017791
15.468
8.627
8.507
7.608
8.144
7.982
8.084
8.070
8.080
8.053
8.088
6.672
7.485

1
2
3
4
5
6
7
8
9
10
11

JZ.017791
3.775
7.884
7.655
7.919
8.145
8.086
8.041
8.172
8.047
8.220
8.078

!1000
VN799 BIOTITE
Laser

!1000
VN357 BIOTITE
Population

1
2
3
4
5
6
7
8
9

10
11
12

JZ.018342
6.841
1.726
7.834
7.687
7.795
7.739
8.128
8.616
8.599
7.944
7.785
7.770
!1000

VN798 BIOTITE
Laser

1
2
3
4
5
6
7

JZ.017791
0.500
6.758
8.126
8.142
7.856
8.014
7.909

0.1
0.7
18.1
25.8
31.5
36.0
41.5

94.3
34.4
1.8
1.4
3.8
2.8
3.6

15.9G72
204.8G19
243.6G1.6
244.0G1.9
236.0G2.8

240.4G3.8
237.5G3.9
(continued on next page)


672

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Table 6 (continued)
Sample

40Ar*/39Ar
8
9
10
11
12
13
14
15
16

8.293
8.168
8.168
8.226
7.908
7.960
8.220

8.171
7.959

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

%Atm Ar

Age(Ma)G2 s

0.001
0.024
0.005
0.045
0.135
0.098
0.070
0.051
0.036

0.120
0.121
0.122
0.119
0.121

0.121
0.119
0.120
0.124

0.039
0.011
0.053
0.056
0.080
0.032
0.044
0.000
0.014

46.8
0.1
60.8
0.7
66.9
0.1
70.6
1.3
72.4
3.9
77.1
2.9
81.7
2.0
84.4

1.5
99.9
1.0
Total ageZ241.8G2.3 Ma

248.2G4.2
244.7G1.5
244.7G2.7
246.4G4.8
237.4G4.8
238.9G3.02
246.2G2.8
244.8G3.7
238.9G1.16

1.302
0.051
0.288
0.070
0.047
0.043
0.088
0.057
0.007
0.059
0.039
0.075
0.058
0.093
0.113

0.156

0.104
0.103
0.111
0.120
0.121
0.123
0.124
0.121
0.120
0.123
0.119
0.119
0.120
0.120
0.121
0.119

0.208
0.002
0.047
0.030
0.018
0.016
0.016
0.014
0.018
0.012
0.003

0.003
0.011
0.000
0.010
0.030

0.4
38.4
0.6
1.5
6.0
8.5
12.8
2.0
22.0
1.3
32.6
1.2
46.1
2.6
54.9
1.6
61.0
0.2
64.3
1.7
79.3
1.1
85.2
2.2

88.5
1.7
94.8
2.7
97.8
3.3
99.9
4.6
Total ageZ243.0G2.4 Ma

180.2G25
282.6G11
247.0G2.5
244.0G1.7
243.8G1.8
240.1G2.3
236.7G3.2
243.0G2.2
247.0G2.6
239.2G3.6
248.0G1.5
247.0G2.1
246.1G3.8
242.4G1.6
238.9G3.3
240.8G3.9

2.164
0.404
0.153

0.074
0.104
0.051
0.133
0.125
0.150
0.378
0.386
0.524
0.229
0.071

0.094
0.111
0.118
0.119
0.119
0.118
0.117
0.116
0.118
0.114
0.117
0.112
0.120
0.120

0.078
0.033
0.022

0.037
0.007
0.037
0.004
0.019
0.059
0.050
0.127
0.148
0.051
0.051

0.7
63.9
2.5
11.9
10.0
4.5
20.5
2.1
30.8
3.0
37.2
1.5
45.8
3.9
55.1
3.6
62.6
4.4

68.4
11.1
70.9
11.4
73.2
15.5
79.6
6.7
99.9
2.1
Total age Z242.2G2.3 Ma

118.7G8.4
237.7G4.7
243.5G1.7
245.3G1.9
244.8G1.2
249.0G2.3
246.3G2.5
247.7G2.0
242.8G2.4
234.9G3.0
227.1G5.2
227.7G4.7
234.0G2.5
245.0G1.3

0.342
1.745
0.886

0.147
0.131
0.112
0.165
0.197
0.216
0.147
0.128
0.148
0.123

0.052
0.151
0.113
0.122
0.119
0.118
0.116
0.112
0.109
0.115
0.115
0.114
0.115

0.002
0.122
0.016
0.006
0.006

0.003
0.016
0.038
0.053
0.044
0.053
0.100
0.193

!1000
VN813 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

JZ.017791
5.907
9.531
8.248
8.143
8.135
8.003
7.883
8.105
8.248
7.971
8.283
8.25
8.217
8.084
7.961
8.028
!1000

VN808 BIOTITE
Laser

1
2
3
4
5
6
7
8

9
10
11
12
13
14

JZ.017791
3.823
7.916
8.123
8.189
8.171
8.320
8.224
8.273
8.100
7.818
7.540
7.564
7.785
8.178
!1000

VN364 BIOTITE
Laser

1
2
3

4
5
6
7
8
9
10
11
12
13

JZ.017791
17.369
3.199
6.545
7.830
8.081
8.199
8.231
8.406
8.548
8.328
8.361
8.389
8.402

0.2
2.0
7.1
17.0

28.2
36.8
47.2
53.3
61.8
72.7
79.4
84.1
86.3

10.1
51.5
26.1
4.3
3.8
3.3
4.9
5.8
6.4
4.3
3.8
4.3
3.6

485.8G115
99.86G15
198.7G5.4
235.3G3.6
242.3G2.3
245.6G2.3

246.5G2.1
251.4G3.1
255.4G2.7
249.2G1.7
250.1G2.3
250.9G4.0
251.3G1.
(continued on next page)


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

673

Table 6 (continued)
Sample

40Ar*/39Ar
14
15
16
17

8.428
8.416
8.422
8.176

36Ar/40Ar

39Ar/40Ar

37Ar/39Ar

%39Ar

%Atm Ar

Age(Ma)G2 s

0.202
0.291
0.283
0.232

0.112
0.109
0.109
0.114

0.076
0.013
0.154
0.040

89.7
5.9
92.2
8.6
94.7

8.3
100.0
6.8
Total age Z242.8G2.4 Ma

252.0G6.1
251.7G10
251.9G7.1
245.0G3.8

2.176
0.503
0.892
0.918
0.000
0.001
0.015
0.000
0.016
0.004
0.025
0.000
0.021

0.342
0.181
0.143
0.162
0.14
0.138

0.14
0.137
0.133
0.137
0.137
0.137
0.134

0.699
0.202
0.385
0.394
0.001
0.011
0.040
0.006
0.025
0.007
0.047
0.046
0.142

0.8
64.3
1.8
14.8
3.6
26.3
12.1
27.1

27.5
0.0
38.1
0.0
42.0
0.4
44.7
0.0
48.8
0.4
56.9
0.1
78.3
0.7
95.3
0.0
99.9
0.6
Total age Z247.8 G4.7 Ma

39.7G53
172.5G42
187.4G23
164.8G5.7
255.9G2.7
258.0G0.6
254.8G1.4
259.8G3.1
265.9G0.6
261.1G5.4

259.6G2.0
260.9G0.7
264.7G0.9

3.130
1.761
0.983
0.658
0.466
0.447
0.452
0.477
0.376
0.320
1.122

0.008
0.054
0.074
0.088
0.095
0.094
0.097
0.098
0.100
0.088
0.078

0.085
0.074

0.057
0.076
0.052
0.083
0.164
0.289
0.096
0.366
0.108

9.7
92.5
22.5
52.0
33.7
29.0
48.7
19.4
62.0
13.7
69.5
13.2
82.5
13.3
90.5
14.1
96.1
11.1
99.3
9.4

100.0
33.1
Total ageZ267.7G3.3 Ma

276.9G42.3
261.7G3.3
278.2G3.9
268.1G1.6
266.3G1.9
269.6G3.4
261.9G2
256.4G2.8
259.4G3.7
298.3G3.6
251.4G21

!1000
VN389 BIOTITE
Laser

1
2
3
4
5
6
7
8
9
10

11
12
13

JZ.021358
1.041
4.698
5.125
4.480
7.136
7.199
7.104
7.253
7.437
7.291
7.246
7.287
7.400
!1000

VN522 BIOTITE
Laser

1
2
3
4
5
6
7

8
9
10
11

JZ.017482
9.490
8.928
9.536
9.165
9.098
9.220
8.938
8.734
8.845
10.284
8.551

Ar is radiogenic argon.

River (VN362, VN363, VN805 and VN 811) that yield the
youngest ages.
4.2.1. Song Bien Group
Biotites in VN 414 and VN 415, have the oldest ages, of
405.7G3.8 and 403.4G3.8 Ma, respectively. VN 414 is a
slightly anatectic mesosome of a granulite facies quartzite
with quartz, mesoperthitic microcline, garnet, biotite,
prismatic sillimanite, cordierite, rutile and spinels (pure Fe
and Fe–Zn), cordierite (only in some compositional layers),
rutile, ilmenite and zircon. VN 415 is a metasedimentary

granulite, which looks like a boudinaged restite in which
cordierite–hercynite coronas are well developed. The
mineralogy of these two samples corresponds to the
better-preserved granulite facies primary assemblages in
the granulites, which have been dated in this study. Late
secondary minerals in these two samples are only tiny grains
of diaspore, muscovite and chlorite along microcracks. No
new foliation is observed. They do not show evidence for
any later polymetamorphic reworking and their primary

biotites yield the oldest ages found for these rocks.
Consequently, the plateau ages of these primary biotites
record the youngest possible age limit for the granulite
facies metamorphism.
As shown in Fig. 11, biotites of VN515, VN413 and
VN514 yield intermediate ages of 343.3G4.2, 325.6G3.1
and 304.2G3.6 Ma respectively. Their host rocks are
granulite facies paragneisses: VN514 and VN515 are
slightly anatectic mesosomes and contain tiny muscovites
and chlorites; VN413 is an anatectic leucosome. In
comparison with the two former samples, some biotites
have been transformed to chlorites, or have suffered loss of
Ti, giving rise to exsolution of rutile needles. The cordierite
is much altered, with formation of pinite. The first
explanation for these younger biotite ages is the influence
of a late retrogressive event, as described above, which
results in argon loss. This conclusion is expressed in the
Fig. 11 by the symbol of increasing intensity of reworking.
However, if these younger ages are consistent with the
petrology and mineralogy, the fact that plateau ages were

674

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

relicts of Zn-rich spinel, and Ti-biotite is completely
transformed to oxychlorite and chlorite. Prismatic sillimanite is still present and occurs frequently as inclusions
within chloritoid. Plagioclase and K-feldspar are completely transformed to white micas and a secondary
muscovite has developed as phenoblasts. The new
foliation is prominent and pervasive. Samples VN505
and VN512 represent the most intense, low-to-medium
grade overprint and are typical polymetamorphic granulites where secondary muscovites have nucleated. These
muscovites yield plateau ages at 262.7G3.2 and 270.7G
2.5 Ma. As the muscovites represent a secondary phase,
these ages demonstrate that the granulite facies metamorphism cannot be younger than 262–270 Ma. These
secondary muscovite ages are related to the total
overprint by a late, low-grade facies, as indicated by
metamorphic assemblages in those rocks.
Fig. 10. Synthesis of plateaux ages of charnockites, according to their
geographic position. (1) refers to samples used for calculated average age.
(2) Younger age (VN295, W Song Ba), and older ages (VN800, 813, 808,
364, Song Ba); (VN389, Dak To); (VN522, Bu Nu).

obtained for each sample has to be explained and several
interpretations can be proposed: the plateau ages could
represent the overprint of a subsequent thermotectonic, late,
low-to medium-grade phase. However, age spectra (Fig. 7c–
e) do not provide evidence for a partial re-equilibration,
especially for the less retentive sites, but yield a plateau

related to 80–90% of the 39Ar released. As the plateau ages
are significantly different and span between 304.2G3.6 and
343.3G4.2 Ma, this result contradicts such a hypothesis
which would imply a similar plateau age for all three
samples; the plateau ages represent the closure of the
systems during cooling. But, as these samples are located in
the same unit and very close to each other, such differences
in age are surprising, unless they have been moved
tectonically from their original position.
More probably, the trend of their flat age spectra, which
does not indicate a significant argon loss related to the less
retentive domains, would imply the closure of the Ar
systems at 343, 325 and 304 Ma respectively, representing
the decompressive-retrograde evolution of the granulite
facies metamorphism.
Up-to-now, the conclusion is not obvious, due to the
scarcity of continuous outcrops in this region that makes a
clear knowledge of the structural imbrications of the series
difficult.
4.2.2. Nuoc Dang Group (Kimson formation)
Samples VN505 and VN512 are located in the north
west of the Song Bien area (Fig. 2), along the Nuoc
Dang Brook. The samples are quartz-chloritoid micaschists and contain only relict assemblages of granulite
facies metamorphism: the strongly broken garnets contain

4.2.3. Granulites of the Song Ba Group
VN362, VN363, VN805 and VN811 (Fig. 11) are
granulite facies metapelites to quartzitic metatectic
granulites. They all contain granulite facies parageneses
with Ti-rich biotite, garnet, and prismatic sillimanite.

Matrix biotites yield ages between 241.1G2.4 and
247.8G2.4 Ma that contrast markedly with those of
other granulites from the Song Bien Group where they
cluster around 244 Ma. Because these rocks crop out in a
domain which is largely occupied by intrusive charnockites and the biotites yield a similar age, we interpret this
age as the result of intrusion of the charnockitic material
linked with a local increase of temperature, leading to a
complete resetting of biotites vs. radiogenic argon, and

Fig. 11. Synthesis of plateaux ages of granulites, according to their degree
of reworking and their geographic position.


H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

not as the age of the peak granulite facies metamorphism. This interpretation is also consistent with the age of
the most recycled granulites from Nuoc Dang (260–
270 Ma), and are younger than the age of the less
retrogressed granulites, the biotites of which have ages
around 400 Ma.
Eighteen zircons from a granulite sampled in the same
locality as VN811 has given 23 U–Pb SHRIMP ages
around 253.7G11.6 Ma and one core age of 1404G
34 Ma (Nam et al., 2001). Despite the difference between
the Ar–Ar average data at 244 Ma and U–Pb data at
253 Ma, which is related to the higher closure temperature of the zircon vs. U–Pb system, the concordance of
these results demonstrates that granulites of the Song Ba
Group suffered strong reheating, followed by very rapid
cooling.
Nevertheless, there is still doubt concerning the age of

the granulite facies metamorphic peak: the oldest U–Pb core
age of one zircon at 1404 Ma was interpreted by Nam et al.
(2001), either as a minimum age for the protolith of the
granulites, or reflecting an earlier high-grade metamorphism
in Mid-Proterozoic times (1400–1600 Ma).
Lan et al. (2003) presented new Sm/Nd data from a
sample of granulite, close to our sample VN805, in the
Song Ba Valley, they determined TDM which was 2.7 Ga.
Two significantly different TDM ages were obtained by
the same authors on two charnockites, at 1.9 Ga and
1.5 Ga, both from the Song Ba Valley. According to Lan
et al. (2003), the crust in central Vietnam is not rich in
recycled Archean rocks, but mainly in Proterozoic rocks,
whose ages are between 1 and 2 Ga. But nevertheless,
concerning the granulites, the TDM age of 2.7 Ga of Lan
et al. (2003), and the 2.7 Ga of Nagy et al. (2001) still
cast doubt on the protolith age of these early rocks.
Whatever the interpretation, the oldest Ar–Ar age of
405 Ma from the Song Bien Group probably reflects the
youngest limit of the granulite facies metamorphic peak.
The Kan Nack Complex is formed by high-grade
anatectic granulite facies for which the protolith age is,
perhaps, as old as 1400 Ma. This complex is intruded by
charnockitic magmas. The age of the granulite facies
peak metamorphism appears to be debatable, considering
results obtained by both radiometric methods. U–Pb
SHRIMP data on zircons from one granulite sample lead
to an age of 254 Ma, but Ar–Ar data provide the
youngest limit at 400 Ma, as indicated by samples
containing the best preserved primary granulite facies

assemblages. This large discrepancy can be explained, as
the U–Pb age determinations were not carried out on the
best preserved granulite facies gneisses, which were used
for the argon analysis. U–Pb ages of 254 Ma relate only
to the overprint of high-temperature charnockitic intrusions in the Song Ba Valley. We thus infer that the Ar–
Ar age of 400 Ma obtained on the best preserved
granulite facies gneisses represents a minimum age
(youngest) for the granulite facies metamorphic peak,

675

and may be intermediate between the true peak
metamorphism age and the Permo-Triassic tectonometamorphic event. Until now, we have not succeeded in
separating zircons from this best preserved facies, which
will probably yield an age older than 400 Ma. Subsequently, this complex suffered a decompression P–T–t
path that resulted in younger Ar–Ar ages: a low-tomedium grade metamorphic event overprinted these highgrade rocks, at w265–270 Ma. This was followed by the
widespread intrusion of charnockitic magmas at 240–
245 Ma in the core of the complex. The emplacement of
charnockites was contemporaneous with the thermotectonic episode which affected the entire Truong Son Belt
around 245 Ma.
Except for one specific unit (Dien Binh Unit, to the
east of the Po Ko Fault) the major part of the Kon Tum
Massif, including the Kan Nack Complex was subjected
to a Permo-Triassic tectono-metamorphic episode and
therefore should not be viewed as an independent unit
with respect to the Truong Son Belt. The Kon Tum
Massif clearly plays an integral part in the construction
of the Permo-Triassic structures of the Indochina Block,
although the paucity of continuous outcrops and the lack
of exposed tectonic contacts makes precise reconstruction

difficult. According to the structural and kinematic data
collected along the western border of the Kon Tum
Massif, the N–S Po Ko Suture might have been the site
of the westwards subduction of eastern Indochina (Kon
Tum Block) beneath an intermediate block (western
Indochina or the Khorat Block), located to the east of
Sibumasu. Left-lateral to top-to-the East shearing along
Po Ko Suture, prior to extensional movements, are
consistent with right-lateral shearing in the Truong Son
Belt and accounts for the oblique collision of Indochina
with both South China and Sibumasu-West Indochina, in
Permo-Triassic times (Lepvrier et al., 2004 in press)

Acknowledgements
We are grateful for a fellowship grant awarded to Mr.
Vu Van Tich by the French Embassy in Vietnam. We
have benefited from the financial contribution of the
Institut National des Sciences de l’Univers (Centre
National de la Recherche Scientifique) through the
Programme International de Coope´ration Scientifique
“Vietnam”. The cooperative programs between University Paris 6, University Montpellier 2 and the National
University of Vietnam, Hanoi, also greatly contributed to
the field work. We are deeply indebted to Mr. Nguyen
Xuan Bao and Mr. Trinh Van Long for their help and
knowledge in the field, and for logistical support. Prof.
B. Windley and Dr. A. Carter are warmly thanked for
their valuable comments during the reviewing. All the
Vietnamese people we met in the field are thanked for
their kindness.

676

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677

Appendix. Experimental conditions
Ar–Ar radiometric method was applied, using both
population dating (with a classical HF furnace) and single
grain dating (using a continuous laser). For population
analyses 80–100 mg of pure separated mineral were
encapsulated in evacuated quartz vials which were loaded
as two or three superposed crowns, each of them containing
one monitor. In order to reduce the vertical irradiation
gradient effect, the 40Ar/39Ar ratio measured on each
monitor was used for age calculation for each relatedcrown samples. The duration of irradiation under fast
neutrons was 60 h at the Osiris reactor of Centre d’E´tudes
Nucle´aires in Saclay (France).
For laser analyses, single grain samples were wrapped
in pure Al foil packets, loaded in the can as superposed
layers, each containing a monitor. Irradiation was
undertaken in the Mac Master Reactor in Ontario
(Canada) for 70 h under fast neutrons. For both types
of irradiation, monitors used were the 520.4G1.7 Ma
MMHb-hornblende (Alexander et al., 1978) and the
Caplongue Hornblende 344.5G3 Ma. Laser single grain
analyses were carried out using a LEXEL 3500
continuous 6 W argon-ion laser for stepwise heating
procedure and a MAP 215-50 noble gas mass spectrometer equipped with a Nier source and a JOHNSTON
MM1 electron multiplier for the mass analysis. We
corrected measured isotopes from the blanks, atmospheric

contamination, mass discrimination, and irradiationinduced mass interferences. Radioactive decay of 37Cl
and 39Ar was taken into account. Age calculation was
made using constants recommended by Steiger and Ja¨ger
(1977) and McDougall and Harrison (1988). Reported
errors are 1sigma for plateau and total ages, which
include uncertainties of the monitors and their 40Ar/39Ar
ratios.

References
Alexander, E.C., Mickelson, G.M., Lanphere, M.A. (1978). MM Hb-1: a
new 40Ar/39Ar dating standard United States Geological Survey, Open
file report 78-701, pp. 6–8.
Carter, A., Roques, D., Bristow, C.S., 2000. Denudation history of onshore
central Vietnam: constraints on the Cenozoic evolution of the western
margin of the South China Sea. Tectonophysics 322, 265–277.
Carter, A., Roques, D., Bristow, C., Kinny, P., 2001. Understanding
Mesozoic accretion in Southeast Asia: significance of Triassic
thermotectonism (Indosinian orogeny) in Vietnam. Geology 29 (3),
211–214.
Fromaget, J., 1941. L’Indochine Franc¸aise, sa structure ge´ologique, ses
roches, ses mines et leurs relations possibles avec la tectonique. Bulletin
du Service Ge´ologique de l’Indochine 26, 2.
Ji, S., Martignole, J., 1994. Ductility of garnet as an indicator of
extremely high temperature deformation. Journal of Structural
Geology 16, 985–996.

Jolivet, L., Maluski, H., Beyssac, O., Goffe´, B., Lepvrier, C., Phan
Truong Thi, Nguyen Van Vuong, 1999. Oligo-Miocene Bu Khang
extensional gneiss dome in Vietnam: geodynamic implications.
Geology 27 (1), 67–70.

Katz, M.B., 1993. The Kannack Complex of the Vietnam Kon Tum Massif
of the Indochina Block: an exotic fragment of Precambrian Gondwanaland?, in: Findlay, R.H., Unrug, R., Banks, M.R., Veevers, J.J. (Eds.),
Gondwana 8. Balkema, Rotterdam, pp. 161–164.
Lan, C.Y., Chung, S.L., Long, T.V., Lo, C.H., Lee, T.Y., Mertzman, S.A.,
Shen, J.J.S., 2003. Geochemical and Sr–Nd isotopic constraints from
the Kontum Massif, central Vietnam on the crustal evolution of the
Indochina block. Precambrian Research 122, 7–27.
Leloup, P.H., Arnaud, N., Lacassin, R., Kienast, J.R., Harrison, T.M., Phan
Trong Trinh, Replumaz, A., Tapponnier, P., 2001. New constraints on
the structure, thermochronology, and timing of the Ailao Shan-Red
River Shear Zone, SE Asia. Journal of Geophysical Research 106 (B4 0 ),
6683–6732.
Lepvrier, C., Maluski, H., Vuong, N.V., Roques, D., Axente, V.,
Rangin, C., 1997. Indosinian NW-trending shear zones within the
Truong Son Belt (Vietnam). Tectonophysics 283, 105–127.
Lepvrier, C., Maluski, H., Vu Van Tich, Leyreloup, A., Phan Truong Thi,
Nguyen Van Vuong, 2004. The early Triassic Indosinian orogeny in
Vietnam (Truong Son Belt and Kon Tum Massif); implications for the
geodynamic evolution of Indochina. Tectonophysics Special Volume.
Maluski, H., Lepvrier, C., Roques, D., Nguyen Van Vuong, Phan Van
Quynh, Rangin, C., 1995. Ages 40Ar–39Ar du complexe plutonome´tamorphique de Da Nang-Dai Loc (Vietnam Central). Processus de
superposition des e´pisodes thermotectoniques ce´nozoı¨que et indonesien; Abstract. Cenozoic evolution of the Indochina Peninsula, Workshop Hanoi-Do Son, p. 65.
Maluski, H., Lepvrier, C., 1998. Overprinting metamorphism in Vietnam,
AGU Fall Meeting 1998. Eos 79, 45, 795.
Maluski, H., Lepvrier, C., Phan Truong Thi, Nguyen Van Vuong, 1999.
Early Mesozoic to Cenozoic evolution of orogens in Vietnam: An Ar–
Ar dating synthesis. Proceedings and abstracts of the International
Workshop GPA’99. Journal of Geology-Hanoi B 13/14, 81–86.
Maluski, H., Lepvrier, C., Leyreloup, A., Vu Van Tich, Phan Truong
Thi, 2000. Age du me´tamorphisme, pe´trologie et structure du Massif

de Kon Tum (Vietnam). Abstract. 18e`me Re´union des Sciences de la
Terre, Paris, 186.
Maluski, H., Lepvrier, C., Jolivet, L., Carter, A., Roques, D.,
Beyssac, O., Ta Trong Tang, Nguyen Duc Thang, Avigad, D.,
2001. Ar–Ar and fission-track ages in the Song Chay Massif: Early
Triassic and Cenozoic tectonics in Northern Vietnam. Journal of
Asian Earth Sciences 19 (1/2), 233–248.
Maluski, H., Lepvrier, C., Leyreloup, A., Vu Van Tich, Phan
Truong Thi, 2002. Late-Permian–Early Triassic thermotectonism in
Vietnam (Truong Son Belt and Kon Tum Massif). Geodynamic
Implications, IGCP430 Workshop II: Ha Long Bay, Vietnam, April
1–5 2002.
McDougall, I., Harrison, T.M., 1988. Geochronology and thermochronology by the 40Ar/39Ar method, Oxford monographs on Geology and
Geophysics, vol. 9. Oxford University Press. 212 p.
Metcalfe, I., 1996. Gondwanaland dispersion, Asian accretion and
evolution of eastern Tethys. Australian Journal of Earth Sciences 43,
605–623.
Metcalfe, I., 1999. Gondwana dispersion and Asian accretion: An
overview, in: Metcalfe, I. (Ed.), In: Gondwana Dispersion and Asian
Accretion IGCP 321 Final Results Volume. Balkema, Amsterdam,
pp. 9–28.
Nagy, E.A., Scha¨rer, U., 1999. The late Permian–Early Triassic orogeny in
Indochina: Precise U–Pb dating results from Vietnam, EUG X. Terra
Abstracts 4, 670.
Nagy, E.A., Maluski, H., Lepvrier, C., Scha¨rer, U., Phan Truong Thi,
Leyreloup, A., Vu Van Tich, 2001. Geodynamic significance of the Kon
Tum Massif in central Vietnam: Composite 40Ar/39Ar and U–Pb ages
from Paleozoic to Triassic. Journal of Geology 109, 755–770.

H. Maluski et al. / Journal of Asian Earth Sciences 25 (2005) 653–677
Phan Cu Tien, (22 co-authors), et al., 1989. Geology of Kampuchea, Laos
and Vietnam (Explanatory note to the geological map of Kampuchea,
Laos and Vietnam at 1/1 000 000 scale). Institute of Information and
Documentation of Mines and Geology, Hanoi. 149 pp.
Phan Truong, Thi, 1985. Metamorphic complexes of the Socialist Republic
of Vietnam. Institute of Information and Documentation of Mines and
Geology, Hanoi. 149 pp.
Steiger, R.H., Ja¨gger, E., 1977. Subcommission on geochronology:
convention on the use of decay constants in geo- and cosmo-chronology.
Earth and Planetary Sciences Letters 36, 359–362.
Theye, T., Chopin, C., Grevel, K.D., Ockenga, E., 1997. The assemblage
diasporeCquartz in metamorphic rocks: a petrological, experimental and
thermodynamic study. Journal of Metamorphic Geology 1997;, 1517–1528.
Tran Quoc Hai, 1989. Precambrian stratigraphy of Indochina, In: Geology
of Kampuchea, Laos and Vietnam. Institute of Information and
Documentation of Mines and Geology, Hanoi. 149 pp.

677

Tran Ngoc Nam, Yuji, S., Kentaro, T., Mitsuhiro, T., Phan Van Quynh, Le
Tien Dung, 2001. First SHRIMP U-Pb zircon dating of granulites from
the Kon Tum Massif (Vietnam) and tectonothermal implications.
Journal of Asian Earth Sciences 19 (1/2), 77–84.
Tran Van Tri, 1986. The main tectonic features of Vietnam. First
Conference on Geology of Indochina, I pp. 363–375.
Tung-Yi Lee, Ching-Hua Lo, Sun-Lin Chung, Chin-Yu Chen, PeiLing Wang, Wen-Pin Lin, Nguyen Hoang, Cung Thuong Chi,
Nguyen Trong Yem, 1998. 40Ar/39Ar dating results of neogene
basalts in Vietnam and its tectonic implication, in: Flower, M., SunLin Chung, Ching-Hua Lo, Tung-Yi Lee (Eds.), Mantle Dynamics
and Plate Interactions in East Asia A.G.U. Geodynamics Series 27,

pp. 317–330.
Vu Van Tich, 2004. La Chaıˆne Indosinienne au Vieˆt Nam: Pe´trologie et
Ge´ochronologie du Bloc Me´tamorphique de Kon Tum. The`se de
Doctorat, Universite´ de Montpellier 2, pp. 202.