Bull. Nagoya Univ.Museum
No. 18, 67-73. 2002

Significance of c. 300 Ma CHIME zircon age for post-tectonic
granite from the Hercynian suture zone, Bamian, Afghanistan
SUZUKI Kazuhiro I), NAKAI Yutaka 2), Daniel J. DUNKLEY1)
and ADACHI Mamoru3)
1) Nagoya University Center for Chronological Research2) Aichi University of Education
3) The Nagoya University Museum

Abstract
CHIME dating was conducted on a sample of massive hornblende-bearing biotite granite collectedfrom a Hercynian suture zone in Bamian, Afghanistan. All zircon grains analyzed exhibit concentriczoning typical of crystallization from a granitic magma.

A total of 66 analyses on 12 grains yielded

an isochron age of 298+/–28 Ma. This is the first chronological evidence found for the existence of
post-tectonic late C arboniferous to early Permian magmatism in the Hercynian suture zone ofcentral Asia, although granitoids of this age are widely recognized in the European Hercynian
orogen.
This provides a new constraint on the timing and extent of Hercynian orogenesis from
Europe to Asia.
Introduction
The Afghanistan territory includes an eastern extension of the Hercynian suture zone, modified
by folding caused by the collision of the Indian Plate with the Asian landmass.
The complex geology of the area was first investigated through a joint S oviet-Afghan project lasting from 1958 to
1977. The region is interpreted to include (1) a possiblly Precambrian basement complex; (2) an
Ordovician to lower Devonian passive margin sedimentary succession developed on oceanic crust;(3) an upper Devonian to lower Carboniferous magmatic arc succession; (4) a lower Carboniferous
to Permian rift/passive margin sedimentary succession, and (5) a Triassic continental magmatic
arc succession beneath Jurassic to Neogene sedimentary rocks (Brockfield and Hashmat, 2001).
The stratigraphy of Paleozoic and Mesozoic formations was determined on the basis of index fossils. In contrast, radiometric age data for metamorphic and igneous rocks are scarce. Correlationof metamorphic rocks was carried out solely on the basis of metamorphic grade. Plutonic rocks
were divided into Proterozoic, early Carboniferous, Triassic and Meso-Cenozoic intrusions on thebasis of intrusive relationships.
These estimates, with an absence of late Carboniferous to early
Permian plutonism, are in contrast to recent studies which suggest that voluminous g ranitoids
were emplaced into the European Hercynian orogen during post-orogenic extension at around 300
Ma. A question we address in this paper is whether or not similar c. 300 Ma granitoids exist in the
Hercynian suture zone in Afghanistan.
One of the authors (N.Y.) conducted a broad geologic survey of Afghanistan in 1971. The rocksamples collected were put on view at the Nagoya University Museum during the "Afghanistan"
exhibition held from November 1, 2002 to January 31, 2003. The samples include hornblendebearing biotite granite from Bamian, with a K-rich calc-alkaline affinity tha t is characteristic of- 67 -

granitoids generated during post-orogenic extension in continent-continent c ollisions. To determine the emplacement age, CHIME dating of zircon in the hornblende-bearing biotite granite wascarried out.
Geological outline
Geological information on Afghanistan was summarized on a 1:2,000,000 map which was published in 1995 by the United Nations Economic and Social Commission for Asia and the Pacific(ESCAP) in cooperation with the Department of Mines and Geological Survey, Ministry of Minesand Industries of Afghanistan. Brockfield and Hashmat (2001) have reported details of the stratigraphy. A simplified tectonic map is shown in Fig. 1. The Harirod strike-slip fault and related faults
trend E-W along the Harirod River in central and western Afghanistan, rotate to NE in the north of
Kabul, and continue to the Wanch-Akbayatal fault. These fault systems approximate the Hercynican
suture line postulated by Burtman and Molnar (1993). The Chaman fault runs NNE-SSW in thesoutheastern part of Afghanistan and marks the western boundary of the Indian subcontinent(Jadoon and Khurshid, 1996).

Hercynianfolded region

Wanch-Akbayatal
fault
Badakhshan

Mazar-e Sharif
BamianK

Harirod river
Harirod fault

Kandahar

C
fa ha
ul m
t am

H

i

u
nd

us

h

Precambrian
mass

Kabul

Alpine folded region

Fig. 1. Map showing major faults and Hercynian and Alpine folded areas in Afghanistan, together
with the sampling location (solid circle), Bamian (Simplified and modified from Leven, 1997).

Amphibolite to granulite-facies metamorphic rocks in Badakhshan and the Hindu Kush havebeen correlated to a basement complex in the Pamir Mountains, where 2700-2400 Ma U-Pb isotopic ages were reported (Horeva et al., 1971). Greenschist to amphibolite-facies metamorphic rocks
are also developed in a number of districts. These metamorphic rocks were previously assigned to
the Proterozoic, but currently they are considered to at least partially represent metamorphosed
Ordovician to lower Devonian passive margin successions, due to the presence of ophiolitic me- 68 -

melanges that include greenschist, blueschist, radiolarian chert, metabasalt, metagabbro andserpentinite.
Metamorphic rocks from Bamian to the western Hindu Kush are overlain by basal conglomerates containing unmetamorphosed Visean limestone pebbles, as well as clasts of metasedimentary,acid volcanic and plutonic rocks (Blaise et al., 1993). The conglomerates grade upwards into Permian (Artinskian to Murgabian) limestones. All these lithologies are unconformably overlain by
Triassic intermediate to acid volcanics and volcaniclastic sediments, which represent a continental
magmatic arc succession.
Granitoids with assumed Proterozoic ages occur as sub-conformable bodies associated with highgrade metamorphic rocks in northeastern Afghanistan (Fig. 1). Discordant granitoids intrude metamorphic rocks in northeastern Badakhshan and the western Hindu Kush and have been regarded
as early Carboniferous in age, as some bodies are overlain by middle to upper Carboniferous formations. Large batholiths in the western Hindu Kush are regarded as post-Triassic in age, as some
intrude Triassic volcanic units and volcaniclastic sediments (Boulin, 1988). The batholiths comprise I-type granitoids with Rb-Sr isochron ages of c. 210 Ma and S-type granitoids of c. 190 Ma(Debon et al., 1987). Plutonic and volcanic complexes that occur along the Chaman fault belong toan Alpine magmatic cycle that began in the late Jurassic. No Permo-Carboniferous granitoids
have been reported from the Hercynian fold belt in Afghanistan.
Sample Description
The sample was collected from a granitic pluton north of the Harirod fault, Bamian. According
to the 1:2,000,000 geologic map, the pluton intrudes an undifferentiated lower Carboniferous formation, and is covered by Maastrichtian to Paleogene sediments. The sample is of coarse-grained
hornblende-bearing biotite granite and has no foliation. It consists mainly of quartz, plagioclase
and microcline with lesser amounts of biotite and hornblende. Accessory minerals include allanite,apatite, and zircon. Iron oxides or titanite were observed under the microscope. An XRF analysis of
the sample is given in Table 1. The sample has a calc-alkaline composition with moderately high(4.08 %) K2O, and falls within the high-K calc-alkaline field of Barbarin (1999).
Quartz grains, mostly 1-3 mm in size, show little undulatory extinction. Microcline contains
perthitic blebs that constitute a substantial proportion of individual grains. Plagioclase is partially saussuritized or sericitized. Oscillatory zoning is marked by unaltered portions of oligoclase
and distinct boundaries of saussuritized and sericitized areas (Fig. 2). Biotite is present with apleochroism of X= straw yellow and Y= dark brown, and is partially altered to green chlorite.
Hornblende is also present, with X= pale yellow green, Y= brownish green and Z= bluish green.
Table 1. XRF analysis of hornblende-bearing biotite granite from Bamian, Afghanistan

SiO2
TiO2
Al2O3
S Fe as FeO
MnO
MgO
CaO
Na2O
K2O
P2O5
Total

73.38
0.28
12.89
2.43
0.06
0.56
1.52
3.47
4.07
0.07
98.73

QuartzCorundum
Orthoclase
AlbiteAnorthite
Hypersthene
Ilmenite
Apatite- 69 -

31.85
0.18
24.05
29.36
7.08
5.50
0.53
0.16

Fig. 2. Photomicropgraphs of hornblende-bearing biotite granite from Bamian, one polarised light (a) andcrossed polars (b). Distinct boundaries between unaltered zones and saussuritized and sericitizedzones mark oscillatory zoning of plagioclase.

Allanite and zircon occur mainly in close association with biotite, and sometimes as inclusions.
Allanite is pleochroic from deep reddish brown to pale brown. Most grains are homogeneous, butsome have deep brown centers and pale brown margins. A preliminary analysis suggests thatallanite grains, especially the deep-colored centers, contain significant amounts (c. 0.2 wt.%) of Pb
but a limited range of ThO2 (1.5-3.8 wt.%). Allanite, therefore, was not used for the CHIME dating. Zircon occurs as faceted prisms 0.05-0.3 mm in length, with concentric zoning. Most zircon
grains are transparent and colorless under the microscope, but some portions of U-enriched grains
are metamict.
Zircon grains in conventional polished thin sections were analyzed on a JEOL JCXA-733 electron
microprobe at the Nagoya University Center for Chronological Research. For analytical techniquesand data reduction methods, readers should r efer to Suzuki and Adachi (1991, 1994 and 1998).
Results and Discussion
A total of 123 spots on 12 zircon grains were analyzed (Table 2). The ThO2 contents range fromless than the detection limit (0.005 wt.%) to 0.528 wt.%, and UO2 contents from 0.021 wt.% to 1.02
wt.%. Of these, only 67 spots contain measurable amounts (>0.004 wt%) of PbO. The analytical
data are plotted on a PbO vs. UO2* diagram (Fig. 3) following the CHIME method of Suzuki and
Adachi (1991). All data points, except a highly uraniferous datum (UO2=1.02 wt.%) from grain
Z02, define an isochron of 298+/–28 Ma (MSWD =0.71) with an intercept value of- 0.003+/–0.0008. Since the isochron is well defined and passes through the origin, the CHIME
zircon age is reliable. The concentric zoning and euhedral morphology of individual grains indicatethat the zircon crystals were formed in a magmatic chamber (Hanchar and Miller, 1993). The mea-

- 70 -

Table 2. Electron microprobe analyses of ThO2, UO2 and PbO in zircon from hornblende-bearing biotite
granite from Barmian, Afghanistan. UO2* represent sum of the measured UO2 and UO2 equivalent of the measured ThO2.
Spot X

Y

ThO2

UO2

PbO

Ma

UO2*

Spot X

Y

ThO2

UO2

PbO

Ma

UO2*

Z01 623, 647
Z01 631, 652
Z01 623, 652
Z01 616, 652
Z01 612, 658
Z01 617, 658
Z01 623, 658
Z01 629, 658
Z01 626, 662
Z01 626, 656
Z02 822, 063
Z02 829, 063
Z02 818, 068
Z02 823, 068
Z02 829, 068
Z02 847, 068
Z02 853, 068
Z02 857, 075
Z02 850, 075
Z02 828, 075
Z02 830, 083
Z02 846, 083
Z02 843, 089
Z02 830, 089
Z02 824, 092
Z03 305, 112
Z03 305, 121
Z03 311, 105
Z03 311, 115
Z03 311, 123
Z03 311, 128
Z03 319, 102
Z03 319, 112
Z03 319, 124
Z03 319, 133
Z03 330, 089
Z03 330, 099
Z03 330, 132
Z03 330, 143
Z03 342, 085
Z03 342, 098
Z03 342, 107
Z03 342, 119
Z03 353, 103
Z03 353, 117
Z03 353, 129
Z03 353, 137
Z03 364, 095
Z03 377, 118
Z03 377, 129
Z03 392, 097
Z03 392, 109
Z03 392, 121
Z03 386, 123
Z04 095, 802
Z04 105, 802
Z04 113, 802
Z04 117, 809
Z04 109, 809
Z04 100, 809
Z04 100, 817
Z04 113, 817
Z04 119, 817
Z04 103, 821

0.052
0.152
0.058
0.055
0.117
0.050
0.084
0.048
0.044
0.045
0.032
0.034
0.138
0.093
0.043
0.035
0.041
0.031
0.027
0.108
0.074
0.065
0.169
0.082
0.051
0.119
0.075
0.062
0.031
0.046
0.053
0.228
0.154
0.061
0.038
0.027
0.059
0.061
0.044
0.067
0.081
0.360
0.149
0.436
0.234
0.070
0.054
0.042
0.528
0.060
0.048
0.038
0.030
0.034
0.062
0.100
0.080
0.059
0.079
0.059
0.108
0.073
0.046
0.052

0.089
0.189
0.118
0.091
0.135
0.108
0.131
0.105
0.076
0.076
0.185
0.197
0.339
0.271
0.172
0.190
0.240
0.195
0.139
0.234
0.207
0.243
1.02
0.233
0.182
0.216
0.126
0.116
0.060
0.090
0.126
0.417
0.307
0.187
0.065
0.055
0.062
0.190
0.050
0.139
0.100
0.544
0.339
0.619
0.424
0.180
0.147
0.076
0.519
0.132
0.086
0.050
0.045
0.069
0.100
0.138
0.119
0.088
0.167
0.108
0.193
0.107
0.061
0.092

0.00940.00460.00420.00530.00630.00530.00900.01570.01140.00780.01080.00760.00730.00500.00990.00950.01060.01940.00990.01050.00660.00700.00660.00590.02010.01680.01080.00780.00600.02780.01620.03140.01960.00860.00770.02400.00530.00480.00620.00830.00840.0090
-

292
250
286
228
294
201
318
301
279
308
391
222
263
250
272
303
296
134
281
386
193
342
356
303
302
346
382
274
275
311
308
305
290
312
342
259
259
296
270
417
321
292
-

0.236
0.136
0.108
0.171
0.157
0.195
0.207
0.382
0.299
0.185
0.200
0.253
0.204
0.147
0.267
0.229
0.263
1.08
0.258
0.197
0.253
0.149
0.135
0.142
0.487
0.354
0.205
0.209
0.160
0.654
0.385
0.753
0.496
0.201
0.164
0.681
0.150
0.119
0.169
0.144
0.191
0.226
-

Z05 316, 752
Z05 316, 758
Z05 316, 766
Z05 322, 747
Z05 322, 754
Z05 322, 761
Z05 322, 768
Z05 331, 747
Z05 331, 760
Z05 336, 754
Z06 686, 854
Z06 692, 854
Z06 698, 854
Z06 702, 859
Z06 694, 859
Z06 686, 859
Z06 688, 866
Z06 695, 866
Z06 703, 866
Z06 707, 872
Z07 946, 007
Z07 948, 017
Z07 943, 017
Z07 955, 025
Z07 948, 025
Z07 938, 025
Z07 958, 039
Z07 948, 039
Z07 935, 039
Z07 915, 039
Z07 947, 054
Z07 935, 054
Z07 920, 054
Z07 900, 054
Z07 904, 065
Z07 915, 065
Z07 934, 065
Z07 922, 080
Z07 922, 054
Z07 943, 029
Z08 330, 902
Z08 303, 902
Z08 297, 894
Z08 303, 894
Z08 303, 910
Z08 330, 910
Z08 337, 910
Z08 337, 922
Z08 330, 922
Z08 321, 927
Z09 009, 825
Z10 731, 336
Z11 171, 431
Z11 177, 429
Z11 179, 423
Z11 109, 485
Z11 115, 489
Z11 119, 491
Z12 768, 033

0.040
0.071
0.045
0.081
0.026
0.043
0.065
0.043
0.033
0.074
0.065
0.170
0.198
0.069
0.060
0.073
0.068
0.004
0.063
0.052
0.082
0.054
0.037
0.068
0.047
0.063
0.039
0.050
0.058
0.039
0.053
0.052
0.064
0.104
0.081
0.046
0.039
0.030
0.072
0.057
0.032
0.333
0.202
0.290
0.252
0.017
0.038
0.051
0.033
0.051
0.528
0.196
0.055
0.045
0.024
0.171
0.114
0.182
0.343

0.088
0.115
0.050
0.167
0.074
0.098
0.129
0.057
0.055
0.115
0.117
0.260
0.282
0.135
0.142
0.150
0.134
0.102
0.109
0.085
0.170
0.111
0.090
0.148
0.104
0.101
0.091
0.083
0.171
0.134
0.091
0.088
0.120
0.188
0.170
0.083
0.081
0.094
0.126
0.104
0.042
0.267
0.193
0.236
0.223
0.021
0.068
0.073
0.041
0.038
0.220
0.275
0.105
0.113
0.051
0.287
0.403
0.368
0.308

0.00650.01070.00720.00490.00930.01360.00820.00740.00640.00880.00520.00530.00590.00560.01020.01740.01130.01550.01140.01610.01560.01550.01940.01600.0154

347
404
380
262
219
291
371
313
301
329
226
207
296
188
382
344
324
347
278
308
339
333
324
277
273

0.136
0.192
0.138
0.137
0.313
0.342
0.161
0.173
0.155
0.195
0.170
0.189
0.146
0.221
0.194
0.369
0.255
0.325
0.301
0.382
0.335
0.339
0.437
0.424
0.414

- 71 -

sured age of 298+/–28 Ma is therefore regarded as the emplacement time of the hornblende-bearing biotite granite.

0.04

298±28 Ma(MSWD=0.71)

PbO (wt.%)

0.03

0.02

Analyticaluncertainty

0.01

0

0

0.4

0.8
UO2* (wt.%)

1.2

Fig. 3. Plots of PbO vs. UO2* of zircon grains. Cross is a data point (1.02 wt. % UO2 and134 Ma apparent age) that is not included in the CHIME age calculation. The
error box in the figure represents 2s analytical uncertainty, and error given to age
is of 2s .

The 298+/–28 Ma age corresponds to the Stephanian stage of Carboniferous according to Harland
et al. (1990). The new age does not correspond to previously assigned ages for Hercynian plutonism in Afghanistan. Instead, it may characterize a magmatic episode related to post-thickening
collapse in the Hercynian orogen. Recognized events in the European Hercynian orogen include a
final ductile deformation phase during the Namurian and Westphalian stages, followed by brittle
deformation phase in the Permian (Pereira et al., 1993). These deformation phases represent postthickening extension tectonics that followed the Hercynian continent-continent collision in the
middle Carboniferous (Faure and Becq-Giraudon, 1993). After the ductile deformation stage, large
volumes of granitoids were emplaced into the European Hercynian orogen within a short time range(e.g. Diasa et al., 1998; Almeida1 et al., 1998; Alexandrova et al., 2000; Morillona et al., 2000).
The plutonism is characterized by a predominance of K-rich calc-alkaline granitoids (e.g. Rottura
et al., 1998; Silva et al., 2000). The present study suggests that K-rich calc-alkaline magmatism
related to the post-thickening extension is contemporaneous throughout the Hercynian orogenfrom Europe to Asia.
Acknowledgements
The authors would like to thanks S. Yogo for his assistance in sample preparation, T. Kato and K.
Tsukada for technical assistance and helpful discussions and K. Wakita for providing geologicalinformation of Afghanistan.
References
Alexandrova, P., Cheilletza, A., Deloulea, E. and Cuney, M. (2000) 319±7 Ma crystallization age for theBlond granite (northwest Limousin, French Massif Central) obtained by U/Pb ion-probe dating of zircons.
G. R. Acad. Sci., Paris, II, 330, 617-622.
- 72 -

Almeida, A., Leterrier, J., Noronha, P. and Bertrand, J.M. (1998) U-Pb zircon and monazite geochronology of
the Hercynian two-mica granite composite pluton of Cabeceiras de Basto (Northern Portugal). G. R.
Acad. Sci., Paris, II, 326, 779-785.
Barbarin, B. (1999) A review of th e relationship s between granitoid types, their origins and heir geodynamic
environments. Lithos, 46, 605-626.
Blaise, J., Boulin, J., Bouyx, E., Lardeuax, H. and Vachard, D. (1993) Identification de faunes devoniennes
dans les formations metamorphiques de L'Hindu Kouch occidental, en Afghanistan: implications. G. R.
Acad. Sci., Paris, II, 317, 963-969.
Boulin, J. (1988) Hercynian and Eocimmerian events in Afghanistan and adjoining regions. Tectonophysics,
148, 253-278.
Brookfield, M.E. and Hashmat, A. (2001) The geology and petroleum potential of the North Afghan platform
and adjacent areas (northern Afghanistan, with parts of southern Turkmenistan, Uzbekistan andTajikistan). Earth Sci. Rev., 55, 41-71.
Burtman, V.S. and Molnar, P. (1993) Geological and geophysical evidence for deep subduction of continental
crust beneath the Pamir. Geol. Soc. Am. Sec. Pap. 281, 76pp.
Debon, F., Afzali, H., FeFort, P., Sonet, J. and Zimmrtmann, J.L. (1987) Plutonic rocks and associations in
Afghanistan: typology, age and geodynamics setting. Memoire Sciende de la Terre, Nancy, 49, 132pp.
Dias, G., Leterrier, J., Mendes, A., Simoes, P.P. and Bertrand, J.M. (1998) U-Pb zircon and monazite
geochronology of post-collisional Hercynian granitoids from the Central Iberian Zone (Northern Portugal).
Lithos, 45, 349-369.
Faure, M. and Becq-Giraudon, J.F. (1993) Sur la succession des episodes extensifs au cours du desepaississement
carbonifere du Massif central franeais. G. R. Acad. Sci. Paris, II, 110, 967-973.
Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G. and Smith, D.G. (1990) A geilogic timescale 1989. Cambridge University Press, 262 pp.
Hanchar, J.M. and Miller, C.F. (1993) Zircon zonation patterns revealed by cathodoluminescence and backscattered electron images: implications for interpretation of complex crustal histories. Chem. Geol., 303,
1-13.
Horeva, B.Ja., Iskanderova, A.D. , Shergina, Ju.P. (1971) Age of protoliths from metamorphic series of SW
Pamir, according to the Pb isotope method. Izvestia AN SSSR, ser. Geologicheskaya, 8, 40-46 (in Russian).
Jadoon, I.A.K. and Khushid, A (1996) Gravity and tectonic model across the Sulaiman fold belt and the
Chaman fault zone in western Pakistan and eastern Afghanistan. Tectonophysics, 254, 89-109.
Leven, E. Ja. (1997) Permian stratigraphy and Fusulinida of Afghanistan with their paleogeographic andpaleotectonic implications (translated by T. Yu. Shalashina, edited by C.H. Stevens and D.L. Baars). Geol.
Soc. Am. Sec. Pap. 316, 134pp.
Morillona, A.C., Feraud, G., Sosson, M., Ruffet, G., Crevola, G. and Lerouge, G. (2000) Diachronous coolingon both sides of a major strike-slip fault in the Variscan Maures Massif (south-east France), as deduced
from a detailed 40Ar/39Ar study. Tectonophysics, 321, 103-126.
Pereira E., Ribeiro, A and Meireles, C. (1993) Cisalhamentos hercinios e controlo das mineralizacoes de SnW, Au e U na Zona Centro-Iberica, em Portugal. Cuad. Lab. Xeol. Laxe, 19, 89-119.
Rottura, A., Bargossi, G.M., Gaggianelli, A., Del Moro, A., Vison, D. and Tranne, C.A. (1998) Origin andsignificance of the Permian high-K calc-alkaline magmatism in the central-eastern Southern Alps, Italy.
Lithos, 45, 329-348.
Silva, M.M.V.G., Neiva, A.M.R. and Whitehouse, M.J. (2000) Geochemistry of enclaves and host granites
from the Nelas area, central Portugal, Lithos, 50, 153-170.
Suzuki, K. and Adachi, M. (1991) Precambrian provenance and Silurian metamorphism of the Tsubonosawa
paragneiss in the South Kitakami terrane, Northeast Japan, revealed by the chemical Th-U-total Pb
isochron ages of monazite, zircon and xenotime. Geochemical. J., 25, 357-376.
Suzuki, K. and Adachi, M. (1994) Middle Precambrian detrital monazite and zircon from the Hida gneiss in
the Oki-Dogo Island, Japan: their origin and implication for the correlation of the basement gneiss ofSouthwest Japan and Korea. Tectonophysics, 235, 277-292.
Suzuki, K. and Adachi, M. (1998) Denudation history of the high T/P Ryoke metamorphic belt, Southwest
Japan: constraints from CHIME monazite ages of gneisses and granitoids. J metamorphic Geol., 16, 2337.

- 73 -