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Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai
Journal of Asian Earth Sciences xxx (2014) xxx–xxx
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Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai Pengfei Li a,b,⇑, Chao Yuan c, Min Sun a,b, Xiaoping Long c, Keda Cai d a
Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China Shenzhen Institute of Research and Innovation, The University of Hong Kong, Pokfulam Road, Hong Kong, China c State Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China d Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China b
a r t i c l e
i n f o
Article history: Received 21 August 2014 Received in revised form 2 November 2014 Accepted 3 November 2014 Available online xxxx Keywords: Central Asian Orogenic Belt Chinese Altai Qiongkuer Domain Erqis Shear Zone 40 Ar/39Ar thermochronology
a b s t r a c t The Chinese Altai, as an accretionary orogen developing from the Cambrian to Carboniferous, was modified by Permian deformation, metamorphism and magmatism in response to the collision with the East Junggar. The tectonic processes of the collision and the timing of related deformation and metamorphism are still enigmatic. Here we present new 40Ar/39Ar dating results for granitic gneisses and amphibolites exposed in the Qiongkuer Domain in two areas (Alahake and Fuyun) of the southern Chinese Altai. The amphiboles from both Aalaheke and Fuyun areas yield consistent 40Ar/39Ar plateau ages at 265.9 ± 1.7 Ma and 270.1 ± 3.1 Ma. In contrast, the biotites from two areas show distinct 40Ar/39Ar ages of 232.0 ± 2.1 Ma and 226.8 ± 1.7 Ma for the Alahake area, and 245.1 ± 1.5 Ma and 264.5 ± 2.2 Ma for the Fuyun area, respectively. Given that 40Ar/39Ar ages are younger than the Permian high temperature metamorphism at 299–277 Ma as constrained by metamorphic zircons in the Qiongkuer Domain, we interpret these 40Ar/39Ar ages to record the cooling history of two areas. Compatible amphibole ages in both areas indicate a similar exhumation age along the Qiongkuer Domain cooling through 550 °C at 270–265 Ma, which may have been associated with the development of the sinistral Erqis Shear Zone during the collision between the Chinese Altai and the East Junggar. The subsequent exhumation processes were variable in different areas of the Qiongkuer Domain as showed by the distinct biotite ages, which may indicate along-strike variation of cooling processes from 550 °C to 300 °C in the Qiongkuer Domain. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The Central Asian Orogenic Belt (CAOB), as one of the largest accretionary orogenic systems in the world, records complex geodynamic processes during the Phanerozoic continental growth of Central Asia (Coleman, 1989; Zonenshain et al., 1990; Sßengör et al., 1993; Jahn, 2004; Windley et al., 2007). The formation of such an orogenic belt involved the episodic accretion of island arcs, ophiolites, accretionary complexes, seamounts and micro-continental blocks along the continental margin (Khain et al., 2002; Buslov et al., 2004; Xiao et al., 2004; Zhang et al., 2011), oroclinal bending (Abrajevitch et al., 2008; Xiao et al., 2010; Yi et al., 2013) and the final collision of the Siberian, Baltic, Tarim and North China cratons (S ß engör et al., 1993; Xiao et al., 2003; Windley et al.,
⇑ Corresponding author at: Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, China. Tel.: +852 28578522. E-mail addresses: [email protected], [email protected] (P. Li).
2007; Eizenhöfer et al., 2014). The mechanism of accretionary orogenesis has been controversial, and may have involved the strikeslip duplication and oroclinal bending of a single arc system (S ß engör et al., 1993; S ß engör and Natal’in, 1996) or the amalgamation of multiple arc systems (Windley et al., 2007; Xiao et al., 2010). Given that the final collision of distinct arc systems or cratons has widely overprinted the earlier accretion-related tectonics, it is vital first to unravel the collisional processes in order to understand the earlier accretion and growth mechanisms of the CAOB. The Chinese Altai is located at a key region between Siberia and Kazakhstan, recording the collisional processes between peri-Siberian and Kazakhstan-South Mongolian orogenic systems (Fig. 1a) (Windley et al., 2002). The collisional zone, as represented by the Erqis Shear Zone in the southern Chinese Altai (Fig. 1a), includes a series of folded zones bounded by narrow mylonitic belts or thrusts (Qu and Zhang, 1991, 1994; Laurent-Charvet et al., 2002; Briggs et al., 2007, 2009). The exact collisional processes along the Erqis Shear Zone are still poorly understood due to limited
http://dx.doi.org/10.1016/j.jseaes.2014.11.004 1367-9120/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx
spatial and temporal constraints on the related deformation, metamorphism and magmatism. In order to unravel the collisional processes, it is crucial to firstly determine the exact time of various magmatic, structural, and metamorphic events. Here we focus on the thermal evolution of the southern Chinese Altai in an attempt to unravel its relationship with regional tectonic evolution using 40Ar/39Ar step heating technique. Previous 40 Ar/39Ar work has demonstrated the widespread effect of the Permian thermal events on the southern Chinese Altai (LaurentCharvet et al., 2003; Briggs et al., 2007, 2009). However, such work has mainly focused on the Fuyun area (Fig. 1) across the Erqis Shear Zone. It is necessary to provide the thermochronological constraints along the strike of the orogenic belt to check the effect of Permian thermal events in an orogenic scale. The aim of this paper is to provide 40Ar/39Ar age constraints on the Qiongkuer Domain of the southern Chinese Altai in both Alahake (in the west) and Fuyun (in the east) areas (Fig. 1) in order to constrain the regional thermal evolution along the southern Chinese Altai. The result of this paper shows that amphiboles in both Fuyun and Alahake areas yield a consistent age at 270 Ma, indicating a similar exhumation age along the Qiongkuer Domain cooling through 550 °C. We attribute this stage of cooling to the regional uplift associated with the development of the Erqis Shear Zone.
2. Geological setting The Chinese Altai represents a segment of the Altai-Mongolian terrane in the CAOB (northernmost Xinjiang Uygur Autonomous Region, China), which comprises of the southwestern part of the peri-Siberian orogenic system and is separated from the Kazakhstan-South Mongolian orogenic system (i.e. East Junggar and West Junggar in China) further southwest by the Erqis Shear Zone (Fig. 1) (S ß engör et al., 1993; Windley et al., 2007; Xiao et al., 2010). The Chinese Altai records early Paleozoic accretionary history of the peri-Siberian orogenic system and the late Paleozoic collisional processes with the Kazakhstan-South Mongolian orogenic system (Fig. 1) (Windley et al., 2002; Cai et al., 2011a; Long et al., 2012). The Chinese Altai can be divided into several fault-bounded tectonic domains based on distinct sedimentary and structural styles, which include, from north to south, the Northern Altai Domain, the Central Altai Domain, the Qiongkuer Domain and the Southern Altai Domain (He et al., 1990; Windley et al., 2002; Cai et al., 2011a). The Northern Altai Domain mainly includes Devonian to Carboniferous metasedimentary and metavolcanic rocks with the metamorphic grade up to sub-greenschist facies (Windley et al., 2002). The Central Altai Domain predominantly contains Cambrian to Silurian turbiditic and pyroclastic sequence (Habahe and Kulumuti groups), with the metamorphic grade varying from greenschist to upper amphibolite facies (Windley et al., 2002; Long et al., 2007, 2008). Further south, the Qiongkuer Domain is characterized by the Devonian metavolcanic rocks of the Kangbutiebao Formation and metasedimentary/volcanic sequence of the Altai Formation. Rocks in the Qiongkuer Domain widely experienced high temperature metamorphism with local metamorphic grade up to granulite facies (Fig. 1b), which has been constrained at 299–277 Ma by metamorphic zircons (Li et al., 2014; Wang et al., 2014a; Yang et al., 2014) though an earlier high temperature event may also develop as indicated by 390 Ma metamorphic zircons (Jiang et al., 2010). The Southern Altai Domain is the southernmost tectonic unit of the Chinese Altai. Rocks in this unit are represented by the Erqis Complex, which is characterized by a heterogeneous sequence of foliated amphibolite-grade schists, paraand ortho-gneisses, amphibolites and metachert (Briggs et al., 2007). Structurally, rocks in the Southern Altai Domain was widely
affected by the sinistral Erqis Shear Zone (Qu and Zhang, 1991), in which one high strain mylonitic belt (the Erqis Fault, Fig. 1a) is generally considered to be the boundary between the Chinese Altai and the East Junggar. The Chinese Altai is characterized by the widespread occurrence of granitic intrusions with two major age groups of 400 Ma and 280 Ma (Wang et al., 2006; Yuan et al., 2007; Sun et al., 2009; Cai et al., 2011b). The older group was normally represented by orthogneiss or gneissic granitoid and widely distributed across the whole Chinese Altai (Cai et al., 2011a). The intrusion of these rocks was accompanied by the regional high temperature metamorphism (Jiang et al., 2010), and was proposed to be associated with the ridge-trench interaction (Sun et al., 2009; Cai et al., 2010). The Permian granitoids are generally non-deformed and often occur in rounded shape in the southern Chinese Altai (Fig. 1). The occurrence of this group of granitoids was also overlapped in time with the Permian high temperature metamorphism (Li et al., 2014). The geodynamic setting of the Chinese Altai in the Permian has been in debate, and may involve the activity of mantle plume (Zhang et al., 2012; Tong et al., 2014; Yang et al., 2014; Zhang et al., 2014), slab breakoff (Li et al., 2014), post-collisional extension (Wei et al., 2007; Wang et al., 2014a) and/or large scale strike-slip shearing (Qu and Zhang, 1991, 1994; Laurent-Charvet et al., 2003). 3. Field geology and sample description 3.1. Alahake area In the area of Alahake, rocks mainly include high grade metavolcanic/sedimentary rocks of the Altai Formation (part of the Qiongkuer Domain) (Fig. 2a), in which the internal stratigraphy is not well defined due to the absence of reliable stratigraphic markers and intense deformation. Rocks in this unit are characterized by a penetrative foliation (S1) steeply dipping to north, and the presence of foliated amphibolite layers indicates up to amphibolite facies metamorphism. The sheeted granitic gneiss widely occurs in the southern part of the Altai Formation (Fig. 3a), with the foliation sub-parallel to the regional dominant fabric (S1). To the north of the Altai Formation, the gneissic granitoid of the Taerlang Batholith (Figs. 1 and 2a) was dated to be 460–380 Ma (Wang et al., 2006; Yuan et al., 2007; Cai et al., 2011b). The gneissic granitoid in the area close to the Altai Formation (Fig. 2a) shows the north-dipping fabric consistent with the regional foliation (S1, Fig. 3b) of the Altai Formation, indicating that both of them may be subject to the same deformation event. Three samples were collected for 40Ar/39Ar analysis in this area (Table 1, Fig. 2a). Sample Alt-79 and Alt-129 are granitic gneisses from the Taerlang Batholith to the north of the Altai Formation (Fig. 2a). Sample Alt-115 is a granitic gneiss within the Altai Formation (Fig. 2a), which yielded a U–Pb zircon age of 412 ± 6 Ma (Yuan et al., 2007). 3.2. Fuyun area In the Fuyun area, the Qiongkuer Domain is separated from the neighboring domains by thrust/strike-slip faults and mainly includes two litho-stratigraphic units of the Altai Formation and the Kangbutiebao Formation (Fig. 2b). Spatially, the Kangbutiebao Formation occurs under the Altai Formation, but the exact timing relationship between them is enigmatic due to the scarcity of chronological data. The Altai Formation is represented by a metasedimentary and metavolcanic sequence in the Fuyun area. Li and Sun (2014) recognized three major lithostratigraphic units, including interlayered
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx
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Fig. 1. (a) Simplified geological map of the Chinese Altai after Wang et al. (2009a), Windley et al. (2002) and Cai et al. (2011a). Triassic ages of granitoids are adapted from Wang et al. (2009a). Inset figure shows the location of the Chinese Altai and major tectonic units in Central Asia. C: Chinese Altai; E: East Junggar; W: West Junggar. The topographic image is from Amante and Eakins (2009). (b) Simplified metamorphic map of the Chinese Altai showing distribution of metamorphic zones after Zhuang (1994) and Jiang et al. (2010). Metamorphic zircon ages and P–T data are after Wang et al. (2009b, 2014a) and Li et al. (2014).
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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Fig. 2. Geological map of the Alahake (a) and Fuyun (b) areas after Yuan et al. (2007), Cai et al. (2007) and Briggs et al. (2009). Structural elements in the maps and cross sections are after Qu and Zhang (1991, 1994), Laurent-Charvet et al. (2003) and our observations.
amphibolite and quartzofeldspathic gneiss with minor chert layers at the bottom, amphibole schist in the middle and mica quartz schist on the top. The widespread occurrence of the amphibolite
and amphibole schist indicates up to amphibolite facies metamorphism at the lower part of the Altai Formation. Structurally, a penetrative fabric (S1) was recognized throughout this formation
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx
(a)
(b)
S1 S1
(c)
(d)
Quartzofeldspathic gneiss S1
S1 Amphibolite
Fig. 3. (a) Interlayered granitic gneiss and amphibolite with steeply dipping foliations within the Altai Formation in the Alahake area. (b) Steeply dipping foliation in the gneissic granitoids to the north of the Altai Formation (Alahake area); (c) interlayered quartzofeldspathic gneiss and amphibolite of the Altai Formation in the Fuyun area. (d) Granitic gneiss with the foliation defined by oriented biotite grains and the axial plane of folded quartz layers in the Fuyun area.
Table 1 Sample location, lithology and
40
Ar/39Ar ages.
Sample no
GPS Coordinate
Lithology
Dated mineral
Plateau age
Error (2r)
Location
Alt-79 Alt-115 Alt-129 Fy-11 Fy-27 Fy-34
47°470 47.500 /87°390 08.100 47°410 50.200 /87°410 51.400 47°430 15.600 /87°440 39.300 46°580 10.900 /89°390 17.500 47°130 13.300 /89°190 06.500 47°090 42.900 /89°160 33.100
Granitic gneiss Granitic gneiss Granitic gneiss Granitic gneiss Granitic gneiss Amphibolite
Biotite Biotite Amphibole Biotite Biotite Amphibole
232 226.8 265.9 264.5 245.1 270.1
2.1 1.7 1.7 2.2 1.5 3.1
Alahake Alahake Alahake Fuyun Fuyun Fuyun
(Fig. 3c), and was folded to form macroscopic fold structures (F2) in map scale (Fig. 2b) (Qu and Zhang, 1994; Laurent-Charvet et al., 2003; Li and Sun, 2014). The Kangbutiebao Formation in this area is characterized by the dominant occurrence of orthogneisses and amphibolite layers, with local metamorphic grade up to granulite facies (Li et al., 2014). The gneissic foliation (S1) is widely recognized in this formation, which is generally defined by the oriented biotite grains or the axial plane of folded quart layers (Fig. 3d). A narrow mylonitic belt (Tuerhongshate Shear Zone, Fig. 2b) was recognized in the northern part of the Kangbutiebao Formation with sinistral kinematics (Zhang et al., 1992; Qu and Zhang, 1994; Laurent-Charvet et al., 2002, 2003; Briggs et al., 2009). Three samples were taken for 40Ar/39Ar dating from the Fuyun area (Fig. 2b and Table 1). Sample FY-34 is an amphibolite from the lower part of the Altai Formation (Fig. 2b). Two samples of granitic gneiss (Fy-11 and Fy-27) were collected from the Kangbutiebao Formation (Fig. 2b). 4.
40
Ar/39Ar geochronology
Six samples were collected from the granitic gneiss and amphibolite in the Qiongkuer Domain for 40Ar/39Ar geochronology.
Amphiboles were picked from samples Alt-129 and Fy-34, while biotites were selected from samples Alt-79, Alt-115, Fy-11 and Fy-27 (Table 1). Selected grains were analyzed at the Institute of Geology, China Earthquake Administration (Beijing), following the procedures documented in Chen et al. (1999a, 1999b). The apparent ages on each step are quoted at the 1ó level. Plateau ages were calculated using the ISOPLOT program (Version 3.0, Ludwig, 2003), and the analytical age errors are reported at the 95% confidence level (2ó). Analytical results are presented in the supplementary file and Fig. 4. All samples yielded well-defined plateau ages. In the Alahake area, biotites from Sample Alt-79 (Taerlang Batholith) shows a flat age spectra defining a plateau age at 232.0 ± 2.1 Ma (Fig. 4b), whereas biotites from Sample Alt-115 (granitic gneiss) yielded an ascending spectra that reach one plateau age at 226.8 ± 1.7 Ma at high temperature (Fig. 4b). In contrast, amphiboles from Sample Alt-129 (Taerlang Batholith) yielded an older plateau age at 265.9 ± 1.7 Ma (Fig. 4c). In the Fuyun area, biotites from Sample Fy-11 (granitic geneiss) yielded a plateau age at 264.5 ± 2.2 Ma (Fig. 4d), which is older than the biotite age from the other granitic gneiss (Sample Fy-27) at 245.1 ± 1.5 Ma (Fig. 4e). Amphiboles from Sample Fy-34 (amphibolite) yielded a relatively older plateau age at 270.1 ± 3.1 Ma (Fig. 4f).
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx 500
(a) Alt - 79 ( biotite )
(b) Alt-115 (biotite)
260
400 220
232.0 ± 2.1 Ma
300
226.8 ± 1.7 Ma
180 200
140
100
100
0
60 0
20
40
60
80
0
100
20
39
40
60
80
100
39
Cumulative % Ar Released
Cumulative % Ar Released 320
(c) Alt-129 (amphibole)
420
(d) Fy-11 (biotite) 280
380
340
240
265.9 ± 1.7 Ma 300
264.5 ± 2.2 Ma
200 260 160 220
180
0
20
40
60
80
100
120
0
39
Cumulative % Ar Released
20
40
60
80
100
80
100
39
Cumulative % Ar Released
270
(e) Fy-27 (biotite)
(f) Fy-34 (amphibole)
340
260 300 250 260 240 220
230
270.1 ± 3.1 Ma
245.1 ± 1.5 Ma 180
220
210 0
20
40
60
80
100
140 0
20
40
39
Cumulative % Ar Released Fig. 4.
Cumulative % Ar Released
40
Ar/39Ar step heating results for the dated samples.
5. Discussion 5.1. Interpretation of
60 39
40
Ar/39Ar ages
Samples from the Qiongkuer Domain yielded 40Ar/39Ar plateau ages ranging from 270.1 ± 3.1 Ma to 226.8 ± 1.7 Ma. These ages could represent the timing of either crystallization of dated minerals or cooling of these minerals below the closure temperature (McDougall and Harrison, 1999). Rocks in the Qiongkuer Domain and adjacent areas were widely deformed and subjected to high temperature metamorphism with local metamorphic grade up to granulite facies (Fig. 1b) (Zhuang, 1994; Wei et al., 2007; Wang et al., 2009b, 2014a). The timing of this high temperature event
has been constrained at 299–277 Ma (metamorphic zircons) in both Fuyun and Aletai areas (northeast of Alahake, Fig. 1) (Li et al., 2014; Wang et al., 2014a), although an earlier high temperature metamorphic event may also affect the Qiongkuer Domain as recorded by 390 metamorphic zircons (Long et al., 2007; Jiang et al., 2010). Given that our 40Ar/39Ar ages of dated amphiboles and biotites from the granitic gneiss and amphibolite are slightly younger than the Permian peak metamorphism (Fig. 5), we interpret these ages to represent the cooling time of dated minerals below their closure temperature after the early Permian high temperature metamorphism although the effect of later thermal/metamorphic events cannot be excluded. This interpretation is consistent with the amphibolite facies metamorphism in the areas
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx
The development of the Erqis Shear zone
3
High temperature metamorphism
2
1
210
230
270
250
290
310
Ma 40
39
Ar/ Ar ages of biotites
40
39
Ar/ Ar ages of amphiboles
U-Pb ages of metamorphic zircons
Fig. 5. An age probability diagram shows that 40Ar/39Ar ages of biotites and amphiboles are obviously younger than metamorphic zircon ages from the Qiongkuer Domain. Metamorphic zircon ages of 299.2 ± 3.4 Ma, 292.8 ± 2.3 Ma and 277 ± 2 Ma are adapted from Wang et al. (2009b, 2014a) and Li et al. (2014), whereas the 40Ar/39Ar amphibole plateau age of 277 ± 4 Ma and biotite plateau-like ages of 262 ± 3 and 250 ± 2 Ma are after Shen et al. (2013) and Briggs et al. (2009).
of our samples, and available P-T data in the Qiongkuer Domain that suggests a metamorphic temperature range up to 635– >940 °C (Fig. 1b) (Wang et al., 2009b; Li et al., 2014; Wang et al., 2014a). The three granitic gneiss samples from the Alahake area yielded distinct cooling ages with an amphibole age at 265.9 ± 1.7 Ma older than the two biotite ages of 226.8 ± 1.7 Ma and 232.0 ± 2.1 Ma, which could be attributed to different closure temperature of biotite (350–300 °C) and amphibole (550–500 °C) (McDougall and Harrison, 1999). In the Fuyun area, analyzed amphiboles from amphibolites in the Altai Formation of the Qiongkuer Domain yielded an plateau age at 270.1 ± 3.1 Ma, which is consistent with a published amphibole 40Ar/39Ar plateau age of 277 ± 4 Ma in a similar area (Fig. 2b) (Shen et al., 2013). Such amphibole ages are older than 249–244 Ma isochron age obtained by in-situ total fusion 40 Ar/39Ar dating of amphiboles from amphibolites in the Altai Formation (Laurent-Charvet et al., 2003). We consider that our stepheating age of 270.1 ± 3.1 Ma is more reliable for the timing of amphibole cooling below 550–500 °C because the laser total fusion 40 Ar/39Ar spot ages may be inadequate to combine multiple total fusion spot analyses that actually represent different proportions of gases extracted from different sample reservoirs (Thiede and Vasconcelos, 2010). The biotites separated from granitic gneisses in the Kangbutiebao Formation of the Qiongkuer Domain (Fuyun area) yielded two distinct ages at 245.1 ± 1.5 Ma and 264.5 ± 2.2 Ma, which are slightly younger than the above amphibole 40Ar/39Ar ages and is consistent with the variable biotite plateau-like ages of 250 ± 2 Ma and 262 ± 3 Ma for the Kangbutiebao Formation (Fuyun area, Fig. 2b) (Briggs et al., 2009). Overall, our new 40Ar/39Ar ages indicates the progressive cooling process of the Qiongkuer Domain from 270 Ma to 226 Ma. Amphiboles cooled below 550–500 °C at the same time (270 Ma) in both Fuyun and Taerlang areas. Biotites with lower closure temperature (300–350 °C) yield younger ages than amphiboles (Fig. 5), but show an older age range in the eastern Qiongkuer Domain (Fuyun area) than the western part (Alahake area).
7
The regional cooling is commonly associated with the uplift of geological units in response to the crustal deformation (Stockli, 2005; Reiners and Brandon, 2006). In the case of the southern Chinese Altai, the activity of the Erqis Shear Zone (Fig. 2b) in the Permian could be responsible for the regional uplift. Such a shear zone is characterized by shallowly plunging lineation with both sinistral and southward thrusting kinematics (Qu and Zhang, 1991, 1994). The Qiongkuer Domain, located to the north of the Erqis Shear Zone (Figs. 1 and 2), could be uplifted during the development of the shear zone. The timing of the Erqis Shear Zone is poorly constrained. The granitic dykes cutting the shear zone, yielded 252 Ma zircon age, which places the youngest constraint on this shear zone (Zhang et al., 2012) though slightly older zircon ages for the dykes were also reported (Briggs et al., 2007). Previous 40 Ar/39Ar work demonstrates that the gneiss complex from the Erqis Shear Zone show complex age spectra (Briggs et al., 2007). We consider that the three weighted mean ages reported by Briggs et al. (2007), i.e. 271 ± 7 Ma (amphibole), 275 ± 8 Ma (muscovite) and 257 ± 10 Ma (biotite) with relatively flat age spectra at high temperature step (Briggs et al., 2007), may represent the active time of the Erqis Shear Zone. Given that early stage of cooling of the Qiongkuer Domain below the amphibole closure temperature at 270 Ma is overlapped in time with the development of the Erqis Shear Zone based on available chronological data, we interpret that the sinistral Erqis Shear Zone was responsible for the exhumation of the Qiongkuer Domain before cooling through the closure temperature of amphibole (550–500 °C). Compatible amphibole 40Ar/39Ar ages in both Alahake and Fuyun areas may indicate a similar exhumation age along the Qiongkuer Domain to cool through 550–500 °C. The cooling time below the biotite closure temperature varies in different areas of the Qiongkuer Domain with relatively faster cooling in the east (Fuyun) than the western area (Alahake), which may indicate along-strike variations of cooling processes of the Qiongkuer Domain after cooling below the amphibole closure temperature. Alternatively, the Qiongkuer Domain may be locally affected by later thermal events disturbing the K–Ar clock heterogeneously through the region. Indeed, minor granitic plutons with an age range of 220–210 Ma (Wang et al., 2009a), occurred to the north of the Qiongkuer Domain in the Aletai and Keketuohai areas (Fig. 1a), which could be responsible for the local thermal disturbances of dated biotite grains. Further support for this interpretation, however, would require a regional thermochronological study aiming at the link between the age distribution and the proximity to the late Permian to Triassic plutons. 5.2. Tectonic implications Rocks in the Qiongkuer Domain mainly include Devonian foliated meta-sedimentary/volcanic sequence of the Altai Formation, and orthogneisses or meta-volcanic rocks of the Kangbutiebao Formation (Fig. 1), which were variably interpreted to be the accretionary complex, forearc basin, arc, or back arc basin (Windley et al., 2002; Xu et al., 2003; Xiao et al., 2004, 2009; Wong et al., 2010; Long et al., 2012). Detrital zircons from the Qiongkuer Domain show an age distribution similar to the Cambrian to Silurian Central Altai Domain in the north (Windley et al., 2002; Long et al., 2007, 2010; Jiang et al., 2011; Wang et al., 2014b), indicating the southward accretion of the Qiongkuer Domain with respect to the Central Altai Domain in the Devonian (Fig. 6). As discussed in the previous section, our new 40Ar/39Ar results represent the cooling time of the Qiongkuer Domain following the early Permian tectono-thermal event in the southern Chinese Altai. Such an event is much later than major phase of accretionary orogenesis of the Qiongkuer Domain in the Devonian (Wang et al., 2006; Long
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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Fig. 6. A schematic tectonic model showing the possible evolution processes of the southern Chinese Altai from subduction accretion to the collision with the East Junggar after Li and Sun (2014). See the explanation in the text.
et al., 2007; Yuan et al., 2007; Sun et al., 2008; Xiao et al., 2008; Sun et al., 2009) The reactivity of the Qiongkuer Domain in the Permian is indicated by the widespread influence of the tectono-thermal event. Such an event was accompanied by the widespread intrusion of felsic and mafic magmatic rocks (Zhang et al., 2012; Yang et al., 2014). The geodynamic process of these events has been attributed to the collision between the Chinese Altai and the East Junggar (Qu and Zhang, 1994; Laurent-Charvet et al., 2003; Briggs et al., 2007). However, the exact collisional time and processes are still enigmatic. The existing models involve post-collisional extension (Wei et al., 2007; Wang et al., 2009b, 2014a), mantle plume (Zhang et al., 2012; Tong et al., 2014; Yang et al., 2014; Zhang et al., 2014), slab breakoff (Li et al., 2014) and/or strike-slip shearing (Yang et al., 1994; LaurentCharvet et al., 2003; Li et al., 2014). Given the limited constraints on the spatial and temporal evolution of magmatism, structure, and metamorphism, it is still difficult to evaluate the validity of the above tectonic models. Here we follow Li and Sun (2014) to propose a tentative model to highlight possible geodynamic processes during the collision between the Chinese Altai and the East Junggar, which were further constrained by new chronological data. We emphasize, however, such a model is based on patchy data, and therefore inevitably incorporates various assumptions and potential errors, which can be tested in future studies. It is generally accepted that the Chinese Altai collided with the East Junggar coevally with or prior to the activity of the Erqis Shear Zone, but the exact timing is still in debate and varies from the Carboniferous to Permian (Xiao et al., 2008; Glorie et al., 2012; Tong et al., 2012; Zhang et al., 2014). Given that subduction-related magmatism lasted at least until 313 Ma in the Chinese Altai (Cai et al., 2012), we consider that the initial collision between the Chinese Alai and the East Junggar may have started in the latest
Carboniferous (Fig. 6). The progressive collision eventually resulted in the crustal thickening followed by the orogenic collapse/extension in the early Permian, as indicated by the widespread high temperature metamorphism (Wei et al., 2007; Wang et al., 2009b; Li et al., 2014; Wang et al., 2014a) and sub-horizontal foliations and related orogen-parallel stretching lineations in the Qiongkuer Domain (Fig. 6) (Li and Sun, 2014). The extensional orogenic collapse has been widely recognized in the modern collisional zones such as the Himalayas and Alps (Dewey, 1988; Frisch et al., 2000; Xu et al., 2013), and may play a crucial role during the collision of the Chinese Altai with the East Junggar. The following convergence was characterized by the development of the sinistral Erqis Shear Zone with reversed components (Qu and Zhang, 1994), which may have led to the regional uplift and cooling of the southern Chinese Altai. New 40Ar/39Ar data together with published chronological data are consistent with the above geodynamic processes (Fig. 6). Our 40Ar/39Ar ages constrain a major exhumation event in the Qiongkuer Domain at 270 Ma, consistent with the regional uplift in response to the sinistral shearing deformation in the later stage of collision between the Chinese Altai and the East Junggar. Such an uplift event in the Qiongkuer Domain was later than high temperature metamorphism at 299–277 Ma (Section 5.1 and Fig. 5) that may have been associated with earlier collision of the Chinese Altai with the East Junggar. Overall, the amalgamation of the Chinese Altai with the East Junggar may experience a relatively long period, involving episodic deformation events. 6. Conclusion We present new 40Ar/39Ar ages from six samples for granitic gneiss and amphibolite in two areas (Alahake and Fuyun) of the
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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Qiongkuer Domain in the southern Chinese Altai. Results from both areas show consistent 40Ar/39Ar amphibole plateau ages at 270– 265 Ma. Given that this age range is younger than regional high temperature metamorphism at 299–277 Ma (metamorphic zircons) in the Qiongkuer Domain, we interpret these amphibole ages to be the time of the Qiongkuer Domain cooling below the amphibole closure temperature (550–500 °C). Compatible 40Ar/39Ar amphibole ages in both areas indicate a similar exhumation age cooling through 550–500 °C, which could be attributed to the regional uplift in response to the activity of the sinistral Erqis Shear Zone associated with the collision between the Chinese Altai and the East Junggar. 40Ar/39Ar ages of biotites show a younger age range of 232–226 Ma in the Alahake area, which is younger than two distinct biotite ages of 264 Ma and 245 Ma in the Fuyun areas. Variable 40Ar/39Ar biotite ages may indicate different cooling rates along the Qiongkuer Domain after cooling down to 550– 500 °C. Acknowledgements This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (Grants: 2014CB440801 and 2014CB448000), Hong Kong Research Grant Council (HKU705311P and HKU704712P), National Science Foundation of China (41273048, 41273012), a HKU small grant (201309176226) and a HKU CRCG grant. The manuscript benefited from constructive comments by Xijun Liu and an anonymous reviewer. The work is a contribution of the Joint Laboratory of Chemical Geodynamics between HKU and CAS (Guangzhou Institute of Geochemistry), IGCP 592 and PROCORE France/Hong Kong Joint Research Scheme. References Abrajevitch, A., Van der Voo, R., Bazhenov, M.L., Levashova, N.M., McCausland, P.J.A., 2008. The role of the Kazakhstan orocline in the late Paleozoic amalgamation of Eurasia. Tectonophysics 455, 61–76. Amante, C., Eakins, B.W., 2009. ETOPO1 1 arc-minute global relief model: procedures, data sources and analysis. NOAA Technical Memorandum NESDIS NGDC-24, 19pp. Briggs, S.M., Yin, A., Manning, C.E., Chen, Z.-L., Wang, X.-F., Grove, M., 2007. Late Paleozoic tectonic history of the Ertix Fault in the Chinese Altai and its implications for the development of the Central Asian Orogenic System. Geol. Soc. Am. Bull. 119, 944–960. Briggs, S.M., Yin, A., Manning, C.E., Chen, Z.-L., Wang, X.-F., 2009. Tectonic development of the southern Chinese Altai Range as determined by structural geology, thermobarometry, 40Ar/39Ar thermochronology, and Th/Pb ionmicroprobe monazite geochronology. Geol. Soc. Am. Bull. 121, 1381–1393. Buslov, M.M., Fujiwara, Y., Iwata, K., Semakov, N.N., 2004. Late Paleozoic-Early Mesozoic geodynamics of Central Asia. Gondwana Res. 7, 791–808. Cai, K., Yuan, C., Sun, M., Xiao, W., Chen, H., Long, X., Zhao, Y., Li, J., 2007. Geochemical characteristics and 40Ar–39Ar ages of the amphibolites and gabbros in Tarlang area: implications for tectonic evolution of the Chinese Altai. Acta Petrologica Sinica 23, 877–888 (in Chinese with English abstract). Cai, K., Sun, M., Yuan, C., Zhao, G., Xiao, W., Long, X., Wu, F., 2010. Geochronological and geochemical study of mafic dykes from the northwest Chinese Altai: implications for petrogenesis and tectonic evolution. Gondwana Res. 18, 638– 652. Cai, K., Sun, M., Yuan, C., Long, X., Xiao, W., 2011a. Geological framework and Paleozoic tectonic history of the Chinese Altai, NW China: a review. Russ. Geol. Geophys. 52, 1619–1633. Cai, K., Sun, M., Yuan, C., Zhao, G., Xiao, W., Long, X., Wu, F., 2011b. Prolonged magmatism, juvenile nature and tectonic evolution of the Chinese Altai, NW China: evidence from zircon U–Pb and Hf isotopic study of Paleozoic granitoids. J. Asian Earth Sci. 42, 949–968. Cai, K., Sun, M., Yuan, C., Xiao, W., Zhao, G., Long, X., Wu, F., 2012. Carboniferous mantle-derived felsic intrusion in the Chinese Altai, NW China: implications for geodynamic change of the accretionary orogenic belt. Gondwana Res. 22, 681– 698. Chen, W., Li, Q., Hao, J., Zhou, X., Sun, M., 1999a. New evidence II for MDD model of thermal evolution history of Gangdese batholith. Chin. Sci. Bull. 44, 736–739. Chen, W., Li, Q., Hao, J., Zhou, X., Wan, J., Sun, M., 1999b. The thermal history of Gangdisi magmatism belt and its significance. Science China (D) 29, 9–15 (in Chinese with English abstract). Coleman, R.G., 1989. Continental growth of northwest China. Tectonics 8, 621–635. Dewey, J.F., 1988. Extensional collapse of orogens. Tectonics 7, 1123–1139.
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Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai Pengfei Li a,b,⇑, Chao Yuan c, Min Sun a,b, Xiaoping Long c, Keda Cai d a
Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China Shenzhen Institute of Research and Innovation, The University of Hong Kong, Pokfulam Road, Hong Kong, China c State Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China d Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China b
a r t i c l e
i n f o
Article history: Received 21 August 2014 Received in revised form 2 November 2014 Accepted 3 November 2014 Available online xxxx Keywords: Central Asian Orogenic Belt Chinese Altai Qiongkuer Domain Erqis Shear Zone 40 Ar/39Ar thermochronology
a b s t r a c t The Chinese Altai, as an accretionary orogen developing from the Cambrian to Carboniferous, was modified by Permian deformation, metamorphism and magmatism in response to the collision with the East Junggar. The tectonic processes of the collision and the timing of related deformation and metamorphism are still enigmatic. Here we present new 40Ar/39Ar dating results for granitic gneisses and amphibolites exposed in the Qiongkuer Domain in two areas (Alahake and Fuyun) of the southern Chinese Altai. The amphiboles from both Aalaheke and Fuyun areas yield consistent 40Ar/39Ar plateau ages at 265.9 ± 1.7 Ma and 270.1 ± 3.1 Ma. In contrast, the biotites from two areas show distinct 40Ar/39Ar ages of 232.0 ± 2.1 Ma and 226.8 ± 1.7 Ma for the Alahake area, and 245.1 ± 1.5 Ma and 264.5 ± 2.2 Ma for the Fuyun area, respectively. Given that 40Ar/39Ar ages are younger than the Permian high temperature metamorphism at 299–277 Ma as constrained by metamorphic zircons in the Qiongkuer Domain, we interpret these 40Ar/39Ar ages to record the cooling history of two areas. Compatible amphibole ages in both areas indicate a similar exhumation age along the Qiongkuer Domain cooling through 550 °C at 270–265 Ma, which may have been associated with the development of the sinistral Erqis Shear Zone during the collision between the Chinese Altai and the East Junggar. The subsequent exhumation processes were variable in different areas of the Qiongkuer Domain as showed by the distinct biotite ages, which may indicate along-strike variation of cooling processes from 550 °C to 300 °C in the Qiongkuer Domain. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The Central Asian Orogenic Belt (CAOB), as one of the largest accretionary orogenic systems in the world, records complex geodynamic processes during the Phanerozoic continental growth of Central Asia (Coleman, 1989; Zonenshain et al., 1990; Sßengör et al., 1993; Jahn, 2004; Windley et al., 2007). The formation of such an orogenic belt involved the episodic accretion of island arcs, ophiolites, accretionary complexes, seamounts and micro-continental blocks along the continental margin (Khain et al., 2002; Buslov et al., 2004; Xiao et al., 2004; Zhang et al., 2011), oroclinal bending (Abrajevitch et al., 2008; Xiao et al., 2010; Yi et al., 2013) and the final collision of the Siberian, Baltic, Tarim and North China cratons (S ß engör et al., 1993; Xiao et al., 2003; Windley et al.,
⇑ Corresponding author at: Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, China. Tel.: +852 28578522. E-mail addresses: [email protected], [email protected] (P. Li).
2007; Eizenhöfer et al., 2014). The mechanism of accretionary orogenesis has been controversial, and may have involved the strikeslip duplication and oroclinal bending of a single arc system (S ß engör et al., 1993; S ß engör and Natal’in, 1996) or the amalgamation of multiple arc systems (Windley et al., 2007; Xiao et al., 2010). Given that the final collision of distinct arc systems or cratons has widely overprinted the earlier accretion-related tectonics, it is vital first to unravel the collisional processes in order to understand the earlier accretion and growth mechanisms of the CAOB. The Chinese Altai is located at a key region between Siberia and Kazakhstan, recording the collisional processes between peri-Siberian and Kazakhstan-South Mongolian orogenic systems (Fig. 1a) (Windley et al., 2002). The collisional zone, as represented by the Erqis Shear Zone in the southern Chinese Altai (Fig. 1a), includes a series of folded zones bounded by narrow mylonitic belts or thrusts (Qu and Zhang, 1991, 1994; Laurent-Charvet et al., 2002; Briggs et al., 2007, 2009). The exact collisional processes along the Erqis Shear Zone are still poorly understood due to limited
http://dx.doi.org/10.1016/j.jseaes.2014.11.004 1367-9120/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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spatial and temporal constraints on the related deformation, metamorphism and magmatism. In order to unravel the collisional processes, it is crucial to firstly determine the exact time of various magmatic, structural, and metamorphic events. Here we focus on the thermal evolution of the southern Chinese Altai in an attempt to unravel its relationship with regional tectonic evolution using 40Ar/39Ar step heating technique. Previous 40 Ar/39Ar work has demonstrated the widespread effect of the Permian thermal events on the southern Chinese Altai (LaurentCharvet et al., 2003; Briggs et al., 2007, 2009). However, such work has mainly focused on the Fuyun area (Fig. 1) across the Erqis Shear Zone. It is necessary to provide the thermochronological constraints along the strike of the orogenic belt to check the effect of Permian thermal events in an orogenic scale. The aim of this paper is to provide 40Ar/39Ar age constraints on the Qiongkuer Domain of the southern Chinese Altai in both Alahake (in the west) and Fuyun (in the east) areas (Fig. 1) in order to constrain the regional thermal evolution along the southern Chinese Altai. The result of this paper shows that amphiboles in both Fuyun and Alahake areas yield a consistent age at 270 Ma, indicating a similar exhumation age along the Qiongkuer Domain cooling through 550 °C. We attribute this stage of cooling to the regional uplift associated with the development of the Erqis Shear Zone.
2. Geological setting The Chinese Altai represents a segment of the Altai-Mongolian terrane in the CAOB (northernmost Xinjiang Uygur Autonomous Region, China), which comprises of the southwestern part of the peri-Siberian orogenic system and is separated from the Kazakhstan-South Mongolian orogenic system (i.e. East Junggar and West Junggar in China) further southwest by the Erqis Shear Zone (Fig. 1) (S ß engör et al., 1993; Windley et al., 2007; Xiao et al., 2010). The Chinese Altai records early Paleozoic accretionary history of the peri-Siberian orogenic system and the late Paleozoic collisional processes with the Kazakhstan-South Mongolian orogenic system (Fig. 1) (Windley et al., 2002; Cai et al., 2011a; Long et al., 2012). The Chinese Altai can be divided into several fault-bounded tectonic domains based on distinct sedimentary and structural styles, which include, from north to south, the Northern Altai Domain, the Central Altai Domain, the Qiongkuer Domain and the Southern Altai Domain (He et al., 1990; Windley et al., 2002; Cai et al., 2011a). The Northern Altai Domain mainly includes Devonian to Carboniferous metasedimentary and metavolcanic rocks with the metamorphic grade up to sub-greenschist facies (Windley et al., 2002). The Central Altai Domain predominantly contains Cambrian to Silurian turbiditic and pyroclastic sequence (Habahe and Kulumuti groups), with the metamorphic grade varying from greenschist to upper amphibolite facies (Windley et al., 2002; Long et al., 2007, 2008). Further south, the Qiongkuer Domain is characterized by the Devonian metavolcanic rocks of the Kangbutiebao Formation and metasedimentary/volcanic sequence of the Altai Formation. Rocks in the Qiongkuer Domain widely experienced high temperature metamorphism with local metamorphic grade up to granulite facies (Fig. 1b), which has been constrained at 299–277 Ma by metamorphic zircons (Li et al., 2014; Wang et al., 2014a; Yang et al., 2014) though an earlier high temperature event may also develop as indicated by 390 Ma metamorphic zircons (Jiang et al., 2010). The Southern Altai Domain is the southernmost tectonic unit of the Chinese Altai. Rocks in this unit are represented by the Erqis Complex, which is characterized by a heterogeneous sequence of foliated amphibolite-grade schists, paraand ortho-gneisses, amphibolites and metachert (Briggs et al., 2007). Structurally, rocks in the Southern Altai Domain was widely
affected by the sinistral Erqis Shear Zone (Qu and Zhang, 1991), in which one high strain mylonitic belt (the Erqis Fault, Fig. 1a) is generally considered to be the boundary between the Chinese Altai and the East Junggar. The Chinese Altai is characterized by the widespread occurrence of granitic intrusions with two major age groups of 400 Ma and 280 Ma (Wang et al., 2006; Yuan et al., 2007; Sun et al., 2009; Cai et al., 2011b). The older group was normally represented by orthogneiss or gneissic granitoid and widely distributed across the whole Chinese Altai (Cai et al., 2011a). The intrusion of these rocks was accompanied by the regional high temperature metamorphism (Jiang et al., 2010), and was proposed to be associated with the ridge-trench interaction (Sun et al., 2009; Cai et al., 2010). The Permian granitoids are generally non-deformed and often occur in rounded shape in the southern Chinese Altai (Fig. 1). The occurrence of this group of granitoids was also overlapped in time with the Permian high temperature metamorphism (Li et al., 2014). The geodynamic setting of the Chinese Altai in the Permian has been in debate, and may involve the activity of mantle plume (Zhang et al., 2012; Tong et al., 2014; Yang et al., 2014; Zhang et al., 2014), slab breakoff (Li et al., 2014), post-collisional extension (Wei et al., 2007; Wang et al., 2014a) and/or large scale strike-slip shearing (Qu and Zhang, 1991, 1994; Laurent-Charvet et al., 2003). 3. Field geology and sample description 3.1. Alahake area In the area of Alahake, rocks mainly include high grade metavolcanic/sedimentary rocks of the Altai Formation (part of the Qiongkuer Domain) (Fig. 2a), in which the internal stratigraphy is not well defined due to the absence of reliable stratigraphic markers and intense deformation. Rocks in this unit are characterized by a penetrative foliation (S1) steeply dipping to north, and the presence of foliated amphibolite layers indicates up to amphibolite facies metamorphism. The sheeted granitic gneiss widely occurs in the southern part of the Altai Formation (Fig. 3a), with the foliation sub-parallel to the regional dominant fabric (S1). To the north of the Altai Formation, the gneissic granitoid of the Taerlang Batholith (Figs. 1 and 2a) was dated to be 460–380 Ma (Wang et al., 2006; Yuan et al., 2007; Cai et al., 2011b). The gneissic granitoid in the area close to the Altai Formation (Fig. 2a) shows the north-dipping fabric consistent with the regional foliation (S1, Fig. 3b) of the Altai Formation, indicating that both of them may be subject to the same deformation event. Three samples were collected for 40Ar/39Ar analysis in this area (Table 1, Fig. 2a). Sample Alt-79 and Alt-129 are granitic gneisses from the Taerlang Batholith to the north of the Altai Formation (Fig. 2a). Sample Alt-115 is a granitic gneiss within the Altai Formation (Fig. 2a), which yielded a U–Pb zircon age of 412 ± 6 Ma (Yuan et al., 2007). 3.2. Fuyun area In the Fuyun area, the Qiongkuer Domain is separated from the neighboring domains by thrust/strike-slip faults and mainly includes two litho-stratigraphic units of the Altai Formation and the Kangbutiebao Formation (Fig. 2b). Spatially, the Kangbutiebao Formation occurs under the Altai Formation, but the exact timing relationship between them is enigmatic due to the scarcity of chronological data. The Altai Formation is represented by a metasedimentary and metavolcanic sequence in the Fuyun area. Li and Sun (2014) recognized three major lithostratigraphic units, including interlayered
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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Fig. 1. (a) Simplified geological map of the Chinese Altai after Wang et al. (2009a), Windley et al. (2002) and Cai et al. (2011a). Triassic ages of granitoids are adapted from Wang et al. (2009a). Inset figure shows the location of the Chinese Altai and major tectonic units in Central Asia. C: Chinese Altai; E: East Junggar; W: West Junggar. The topographic image is from Amante and Eakins (2009). (b) Simplified metamorphic map of the Chinese Altai showing distribution of metamorphic zones after Zhuang (1994) and Jiang et al. (2010). Metamorphic zircon ages and P–T data are after Wang et al. (2009b, 2014a) and Li et al. (2014).
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Fig. 2. Geological map of the Alahake (a) and Fuyun (b) areas after Yuan et al. (2007), Cai et al. (2007) and Briggs et al. (2009). Structural elements in the maps and cross sections are after Qu and Zhang (1991, 1994), Laurent-Charvet et al. (2003) and our observations.
amphibolite and quartzofeldspathic gneiss with minor chert layers at the bottom, amphibole schist in the middle and mica quartz schist on the top. The widespread occurrence of the amphibolite
and amphibole schist indicates up to amphibolite facies metamorphism at the lower part of the Altai Formation. Structurally, a penetrative fabric (S1) was recognized throughout this formation
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(a)
(b)
S1 S1
(c)
(d)
Quartzofeldspathic gneiss S1
S1 Amphibolite
Fig. 3. (a) Interlayered granitic gneiss and amphibolite with steeply dipping foliations within the Altai Formation in the Alahake area. (b) Steeply dipping foliation in the gneissic granitoids to the north of the Altai Formation (Alahake area); (c) interlayered quartzofeldspathic gneiss and amphibolite of the Altai Formation in the Fuyun area. (d) Granitic gneiss with the foliation defined by oriented biotite grains and the axial plane of folded quartz layers in the Fuyun area.
Table 1 Sample location, lithology and
40
Ar/39Ar ages.
Sample no
GPS Coordinate
Lithology
Dated mineral
Plateau age
Error (2r)
Location
Alt-79 Alt-115 Alt-129 Fy-11 Fy-27 Fy-34
47°470 47.500 /87°390 08.100 47°410 50.200 /87°410 51.400 47°430 15.600 /87°440 39.300 46°580 10.900 /89°390 17.500 47°130 13.300 /89°190 06.500 47°090 42.900 /89°160 33.100
Granitic gneiss Granitic gneiss Granitic gneiss Granitic gneiss Granitic gneiss Amphibolite
Biotite Biotite Amphibole Biotite Biotite Amphibole
232 226.8 265.9 264.5 245.1 270.1
2.1 1.7 1.7 2.2 1.5 3.1
Alahake Alahake Alahake Fuyun Fuyun Fuyun
(Fig. 3c), and was folded to form macroscopic fold structures (F2) in map scale (Fig. 2b) (Qu and Zhang, 1994; Laurent-Charvet et al., 2003; Li and Sun, 2014). The Kangbutiebao Formation in this area is characterized by the dominant occurrence of orthogneisses and amphibolite layers, with local metamorphic grade up to granulite facies (Li et al., 2014). The gneissic foliation (S1) is widely recognized in this formation, which is generally defined by the oriented biotite grains or the axial plane of folded quart layers (Fig. 3d). A narrow mylonitic belt (Tuerhongshate Shear Zone, Fig. 2b) was recognized in the northern part of the Kangbutiebao Formation with sinistral kinematics (Zhang et al., 1992; Qu and Zhang, 1994; Laurent-Charvet et al., 2002, 2003; Briggs et al., 2009). Three samples were taken for 40Ar/39Ar dating from the Fuyun area (Fig. 2b and Table 1). Sample FY-34 is an amphibolite from the lower part of the Altai Formation (Fig. 2b). Two samples of granitic gneiss (Fy-11 and Fy-27) were collected from the Kangbutiebao Formation (Fig. 2b). 4.
40
Ar/39Ar geochronology
Six samples were collected from the granitic gneiss and amphibolite in the Qiongkuer Domain for 40Ar/39Ar geochronology.
Amphiboles were picked from samples Alt-129 and Fy-34, while biotites were selected from samples Alt-79, Alt-115, Fy-11 and Fy-27 (Table 1). Selected grains were analyzed at the Institute of Geology, China Earthquake Administration (Beijing), following the procedures documented in Chen et al. (1999a, 1999b). The apparent ages on each step are quoted at the 1ó level. Plateau ages were calculated using the ISOPLOT program (Version 3.0, Ludwig, 2003), and the analytical age errors are reported at the 95% confidence level (2ó). Analytical results are presented in the supplementary file and Fig. 4. All samples yielded well-defined plateau ages. In the Alahake area, biotites from Sample Alt-79 (Taerlang Batholith) shows a flat age spectra defining a plateau age at 232.0 ± 2.1 Ma (Fig. 4b), whereas biotites from Sample Alt-115 (granitic gneiss) yielded an ascending spectra that reach one plateau age at 226.8 ± 1.7 Ma at high temperature (Fig. 4b). In contrast, amphiboles from Sample Alt-129 (Taerlang Batholith) yielded an older plateau age at 265.9 ± 1.7 Ma (Fig. 4c). In the Fuyun area, biotites from Sample Fy-11 (granitic geneiss) yielded a plateau age at 264.5 ± 2.2 Ma (Fig. 4d), which is older than the biotite age from the other granitic gneiss (Sample Fy-27) at 245.1 ± 1.5 Ma (Fig. 4e). Amphiboles from Sample Fy-34 (amphibolite) yielded a relatively older plateau age at 270.1 ± 3.1 Ma (Fig. 4f).
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx 500
(a) Alt - 79 ( biotite )
(b) Alt-115 (biotite)
260
400 220
232.0 ± 2.1 Ma
300
226.8 ± 1.7 Ma
180 200
140
100
100
0
60 0
20
40
60
80
0
100
20
39
40
60
80
100
39
Cumulative % Ar Released
Cumulative % Ar Released 320
(c) Alt-129 (amphibole)
420
(d) Fy-11 (biotite) 280
380
340
240
265.9 ± 1.7 Ma 300
264.5 ± 2.2 Ma
200 260 160 220
180
0
20
40
60
80
100
120
0
39
Cumulative % Ar Released
20
40
60
80
100
80
100
39
Cumulative % Ar Released
270
(e) Fy-27 (biotite)
(f) Fy-34 (amphibole)
340
260 300 250 260 240 220
230
270.1 ± 3.1 Ma
245.1 ± 1.5 Ma 180
220
210 0
20
40
60
80
100
140 0
20
40
39
Cumulative % Ar Released Fig. 4.
Cumulative % Ar Released
40
Ar/39Ar step heating results for the dated samples.
5. Discussion 5.1. Interpretation of
60 39
40
Ar/39Ar ages
Samples from the Qiongkuer Domain yielded 40Ar/39Ar plateau ages ranging from 270.1 ± 3.1 Ma to 226.8 ± 1.7 Ma. These ages could represent the timing of either crystallization of dated minerals or cooling of these minerals below the closure temperature (McDougall and Harrison, 1999). Rocks in the Qiongkuer Domain and adjacent areas were widely deformed and subjected to high temperature metamorphism with local metamorphic grade up to granulite facies (Fig. 1b) (Zhuang, 1994; Wei et al., 2007; Wang et al., 2009b, 2014a). The timing of this high temperature event
has been constrained at 299–277 Ma (metamorphic zircons) in both Fuyun and Aletai areas (northeast of Alahake, Fig. 1) (Li et al., 2014; Wang et al., 2014a), although an earlier high temperature metamorphic event may also affect the Qiongkuer Domain as recorded by 390 metamorphic zircons (Long et al., 2007; Jiang et al., 2010). Given that our 40Ar/39Ar ages of dated amphiboles and biotites from the granitic gneiss and amphibolite are slightly younger than the Permian peak metamorphism (Fig. 5), we interpret these ages to represent the cooling time of dated minerals below their closure temperature after the early Permian high temperature metamorphism although the effect of later thermal/metamorphic events cannot be excluded. This interpretation is consistent with the amphibolite facies metamorphism in the areas
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The development of the Erqis Shear zone
3
High temperature metamorphism
2
1
210
230
270
250
290
310
Ma 40
39
Ar/ Ar ages of biotites
40
39
Ar/ Ar ages of amphiboles
U-Pb ages of metamorphic zircons
Fig. 5. An age probability diagram shows that 40Ar/39Ar ages of biotites and amphiboles are obviously younger than metamorphic zircon ages from the Qiongkuer Domain. Metamorphic zircon ages of 299.2 ± 3.4 Ma, 292.8 ± 2.3 Ma and 277 ± 2 Ma are adapted from Wang et al. (2009b, 2014a) and Li et al. (2014), whereas the 40Ar/39Ar amphibole plateau age of 277 ± 4 Ma and biotite plateau-like ages of 262 ± 3 and 250 ± 2 Ma are after Shen et al. (2013) and Briggs et al. (2009).
of our samples, and available P-T data in the Qiongkuer Domain that suggests a metamorphic temperature range up to 635– >940 °C (Fig. 1b) (Wang et al., 2009b; Li et al., 2014; Wang et al., 2014a). The three granitic gneiss samples from the Alahake area yielded distinct cooling ages with an amphibole age at 265.9 ± 1.7 Ma older than the two biotite ages of 226.8 ± 1.7 Ma and 232.0 ± 2.1 Ma, which could be attributed to different closure temperature of biotite (350–300 °C) and amphibole (550–500 °C) (McDougall and Harrison, 1999). In the Fuyun area, analyzed amphiboles from amphibolites in the Altai Formation of the Qiongkuer Domain yielded an plateau age at 270.1 ± 3.1 Ma, which is consistent with a published amphibole 40Ar/39Ar plateau age of 277 ± 4 Ma in a similar area (Fig. 2b) (Shen et al., 2013). Such amphibole ages are older than 249–244 Ma isochron age obtained by in-situ total fusion 40 Ar/39Ar dating of amphiboles from amphibolites in the Altai Formation (Laurent-Charvet et al., 2003). We consider that our stepheating age of 270.1 ± 3.1 Ma is more reliable for the timing of amphibole cooling below 550–500 °C because the laser total fusion 40 Ar/39Ar spot ages may be inadequate to combine multiple total fusion spot analyses that actually represent different proportions of gases extracted from different sample reservoirs (Thiede and Vasconcelos, 2010). The biotites separated from granitic gneisses in the Kangbutiebao Formation of the Qiongkuer Domain (Fuyun area) yielded two distinct ages at 245.1 ± 1.5 Ma and 264.5 ± 2.2 Ma, which are slightly younger than the above amphibole 40Ar/39Ar ages and is consistent with the variable biotite plateau-like ages of 250 ± 2 Ma and 262 ± 3 Ma for the Kangbutiebao Formation (Fuyun area, Fig. 2b) (Briggs et al., 2009). Overall, our new 40Ar/39Ar ages indicates the progressive cooling process of the Qiongkuer Domain from 270 Ma to 226 Ma. Amphiboles cooled below 550–500 °C at the same time (270 Ma) in both Fuyun and Taerlang areas. Biotites with lower closure temperature (300–350 °C) yield younger ages than amphiboles (Fig. 5), but show an older age range in the eastern Qiongkuer Domain (Fuyun area) than the western part (Alahake area).
7
The regional cooling is commonly associated with the uplift of geological units in response to the crustal deformation (Stockli, 2005; Reiners and Brandon, 2006). In the case of the southern Chinese Altai, the activity of the Erqis Shear Zone (Fig. 2b) in the Permian could be responsible for the regional uplift. Such a shear zone is characterized by shallowly plunging lineation with both sinistral and southward thrusting kinematics (Qu and Zhang, 1991, 1994). The Qiongkuer Domain, located to the north of the Erqis Shear Zone (Figs. 1 and 2), could be uplifted during the development of the shear zone. The timing of the Erqis Shear Zone is poorly constrained. The granitic dykes cutting the shear zone, yielded 252 Ma zircon age, which places the youngest constraint on this shear zone (Zhang et al., 2012) though slightly older zircon ages for the dykes were also reported (Briggs et al., 2007). Previous 40 Ar/39Ar work demonstrates that the gneiss complex from the Erqis Shear Zone show complex age spectra (Briggs et al., 2007). We consider that the three weighted mean ages reported by Briggs et al. (2007), i.e. 271 ± 7 Ma (amphibole), 275 ± 8 Ma (muscovite) and 257 ± 10 Ma (biotite) with relatively flat age spectra at high temperature step (Briggs et al., 2007), may represent the active time of the Erqis Shear Zone. Given that early stage of cooling of the Qiongkuer Domain below the amphibole closure temperature at 270 Ma is overlapped in time with the development of the Erqis Shear Zone based on available chronological data, we interpret that the sinistral Erqis Shear Zone was responsible for the exhumation of the Qiongkuer Domain before cooling through the closure temperature of amphibole (550–500 °C). Compatible amphibole 40Ar/39Ar ages in both Alahake and Fuyun areas may indicate a similar exhumation age along the Qiongkuer Domain to cool through 550–500 °C. The cooling time below the biotite closure temperature varies in different areas of the Qiongkuer Domain with relatively faster cooling in the east (Fuyun) than the western area (Alahake), which may indicate along-strike variations of cooling processes of the Qiongkuer Domain after cooling below the amphibole closure temperature. Alternatively, the Qiongkuer Domain may be locally affected by later thermal events disturbing the K–Ar clock heterogeneously through the region. Indeed, minor granitic plutons with an age range of 220–210 Ma (Wang et al., 2009a), occurred to the north of the Qiongkuer Domain in the Aletai and Keketuohai areas (Fig. 1a), which could be responsible for the local thermal disturbances of dated biotite grains. Further support for this interpretation, however, would require a regional thermochronological study aiming at the link between the age distribution and the proximity to the late Permian to Triassic plutons. 5.2. Tectonic implications Rocks in the Qiongkuer Domain mainly include Devonian foliated meta-sedimentary/volcanic sequence of the Altai Formation, and orthogneisses or meta-volcanic rocks of the Kangbutiebao Formation (Fig. 1), which were variably interpreted to be the accretionary complex, forearc basin, arc, or back arc basin (Windley et al., 2002; Xu et al., 2003; Xiao et al., 2004, 2009; Wong et al., 2010; Long et al., 2012). Detrital zircons from the Qiongkuer Domain show an age distribution similar to the Cambrian to Silurian Central Altai Domain in the north (Windley et al., 2002; Long et al., 2007, 2010; Jiang et al., 2011; Wang et al., 2014b), indicating the southward accretion of the Qiongkuer Domain with respect to the Central Altai Domain in the Devonian (Fig. 6). As discussed in the previous section, our new 40Ar/39Ar results represent the cooling time of the Qiongkuer Domain following the early Permian tectono-thermal event in the southern Chinese Altai. Such an event is much later than major phase of accretionary orogenesis of the Qiongkuer Domain in the Devonian (Wang et al., 2006; Long
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
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Fig. 6. A schematic tectonic model showing the possible evolution processes of the southern Chinese Altai from subduction accretion to the collision with the East Junggar after Li and Sun (2014). See the explanation in the text.
et al., 2007; Yuan et al., 2007; Sun et al., 2008; Xiao et al., 2008; Sun et al., 2009) The reactivity of the Qiongkuer Domain in the Permian is indicated by the widespread influence of the tectono-thermal event. Such an event was accompanied by the widespread intrusion of felsic and mafic magmatic rocks (Zhang et al., 2012; Yang et al., 2014). The geodynamic process of these events has been attributed to the collision between the Chinese Altai and the East Junggar (Qu and Zhang, 1994; Laurent-Charvet et al., 2003; Briggs et al., 2007). However, the exact collisional time and processes are still enigmatic. The existing models involve post-collisional extension (Wei et al., 2007; Wang et al., 2009b, 2014a), mantle plume (Zhang et al., 2012; Tong et al., 2014; Yang et al., 2014; Zhang et al., 2014), slab breakoff (Li et al., 2014) and/or strike-slip shearing (Yang et al., 1994; LaurentCharvet et al., 2003; Li et al., 2014). Given the limited constraints on the spatial and temporal evolution of magmatism, structure, and metamorphism, it is still difficult to evaluate the validity of the above tectonic models. Here we follow Li and Sun (2014) to propose a tentative model to highlight possible geodynamic processes during the collision between the Chinese Altai and the East Junggar, which were further constrained by new chronological data. We emphasize, however, such a model is based on patchy data, and therefore inevitably incorporates various assumptions and potential errors, which can be tested in future studies. It is generally accepted that the Chinese Altai collided with the East Junggar coevally with or prior to the activity of the Erqis Shear Zone, but the exact timing is still in debate and varies from the Carboniferous to Permian (Xiao et al., 2008; Glorie et al., 2012; Tong et al., 2012; Zhang et al., 2014). Given that subduction-related magmatism lasted at least until 313 Ma in the Chinese Altai (Cai et al., 2012), we consider that the initial collision between the Chinese Alai and the East Junggar may have started in the latest
Carboniferous (Fig. 6). The progressive collision eventually resulted in the crustal thickening followed by the orogenic collapse/extension in the early Permian, as indicated by the widespread high temperature metamorphism (Wei et al., 2007; Wang et al., 2009b; Li et al., 2014; Wang et al., 2014a) and sub-horizontal foliations and related orogen-parallel stretching lineations in the Qiongkuer Domain (Fig. 6) (Li and Sun, 2014). The extensional orogenic collapse has been widely recognized in the modern collisional zones such as the Himalayas and Alps (Dewey, 1988; Frisch et al., 2000; Xu et al., 2013), and may play a crucial role during the collision of the Chinese Altai with the East Junggar. The following convergence was characterized by the development of the sinistral Erqis Shear Zone with reversed components (Qu and Zhang, 1994), which may have led to the regional uplift and cooling of the southern Chinese Altai. New 40Ar/39Ar data together with published chronological data are consistent with the above geodynamic processes (Fig. 6). Our 40Ar/39Ar ages constrain a major exhumation event in the Qiongkuer Domain at 270 Ma, consistent with the regional uplift in response to the sinistral shearing deformation in the later stage of collision between the Chinese Altai and the East Junggar. Such an uplift event in the Qiongkuer Domain was later than high temperature metamorphism at 299–277 Ma (Section 5.1 and Fig. 5) that may have been associated with earlier collision of the Chinese Altai with the East Junggar. Overall, the amalgamation of the Chinese Altai with the East Junggar may experience a relatively long period, involving episodic deformation events. 6. Conclusion We present new 40Ar/39Ar ages from six samples for granitic gneiss and amphibolite in two areas (Alahake and Fuyun) of the
Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004
P. Li et al. / Journal of Asian Earth Sciences xxx (2014) xxx–xxx
Qiongkuer Domain in the southern Chinese Altai. Results from both areas show consistent 40Ar/39Ar amphibole plateau ages at 270– 265 Ma. Given that this age range is younger than regional high temperature metamorphism at 299–277 Ma (metamorphic zircons) in the Qiongkuer Domain, we interpret these amphibole ages to be the time of the Qiongkuer Domain cooling below the amphibole closure temperature (550–500 °C). Compatible 40Ar/39Ar amphibole ages in both areas indicate a similar exhumation age cooling through 550–500 °C, which could be attributed to the regional uplift in response to the activity of the sinistral Erqis Shear Zone associated with the collision between the Chinese Altai and the East Junggar. 40Ar/39Ar ages of biotites show a younger age range of 232–226 Ma in the Alahake area, which is younger than two distinct biotite ages of 264 Ma and 245 Ma in the Fuyun areas. Variable 40Ar/39Ar biotite ages may indicate different cooling rates along the Qiongkuer Domain after cooling down to 550– 500 °C. Acknowledgements This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (Grants: 2014CB440801 and 2014CB448000), Hong Kong Research Grant Council (HKU705311P and HKU704712P), National Science Foundation of China (41273048, 41273012), a HKU small grant (201309176226) and a HKU CRCG grant. The manuscript benefited from constructive comments by Xijun Liu and an anonymous reviewer. The work is a contribution of the Joint Laboratory of Chemical Geodynamics between HKU and CAS (Guangzhou Institute of Geochemistry), IGCP 592 and PROCORE France/Hong Kong Joint Research Scheme. References Abrajevitch, A., Van der Voo, R., Bazhenov, M.L., Levashova, N.M., McCausland, P.J.A., 2008. The role of the Kazakhstan orocline in the late Paleozoic amalgamation of Eurasia. Tectonophysics 455, 61–76. Amante, C., Eakins, B.W., 2009. ETOPO1 1 arc-minute global relief model: procedures, data sources and analysis. NOAA Technical Memorandum NESDIS NGDC-24, 19pp. Briggs, S.M., Yin, A., Manning, C.E., Chen, Z.-L., Wang, X.-F., Grove, M., 2007. Late Paleozoic tectonic history of the Ertix Fault in the Chinese Altai and its implications for the development of the Central Asian Orogenic System. Geol. Soc. Am. Bull. 119, 944–960. Briggs, S.M., Yin, A., Manning, C.E., Chen, Z.-L., Wang, X.-F., 2009. Tectonic development of the southern Chinese Altai Range as determined by structural geology, thermobarometry, 40Ar/39Ar thermochronology, and Th/Pb ionmicroprobe monazite geochronology. Geol. Soc. Am. Bull. 121, 1381–1393. Buslov, M.M., Fujiwara, Y., Iwata, K., Semakov, N.N., 2004. Late Paleozoic-Early Mesozoic geodynamics of Central Asia. Gondwana Res. 7, 791–808. Cai, K., Yuan, C., Sun, M., Xiao, W., Chen, H., Long, X., Zhao, Y., Li, J., 2007. Geochemical characteristics and 40Ar–39Ar ages of the amphibolites and gabbros in Tarlang area: implications for tectonic evolution of the Chinese Altai. Acta Petrologica Sinica 23, 877–888 (in Chinese with English abstract). Cai, K., Sun, M., Yuan, C., Zhao, G., Xiao, W., Long, X., Wu, F., 2010. Geochronological and geochemical study of mafic dykes from the northwest Chinese Altai: implications for petrogenesis and tectonic evolution. Gondwana Res. 18, 638– 652. Cai, K., Sun, M., Yuan, C., Long, X., Xiao, W., 2011a. Geological framework and Paleozoic tectonic history of the Chinese Altai, NW China: a review. Russ. Geol. Geophys. 52, 1619–1633. Cai, K., Sun, M., Yuan, C., Zhao, G., Xiao, W., Long, X., Wu, F., 2011b. Prolonged magmatism, juvenile nature and tectonic evolution of the Chinese Altai, NW China: evidence from zircon U–Pb and Hf isotopic study of Paleozoic granitoids. J. Asian Earth Sci. 42, 949–968. Cai, K., Sun, M., Yuan, C., Xiao, W., Zhao, G., Long, X., Wu, F., 2012. Carboniferous mantle-derived felsic intrusion in the Chinese Altai, NW China: implications for geodynamic change of the accretionary orogenic belt. Gondwana Res. 22, 681– 698. Chen, W., Li, Q., Hao, J., Zhou, X., Sun, M., 1999a. New evidence II for MDD model of thermal evolution history of Gangdese batholith. Chin. Sci. Bull. 44, 736–739. Chen, W., Li, Q., Hao, J., Zhou, X., Wan, J., Sun, M., 1999b. The thermal history of Gangdisi magmatism belt and its significance. Science China (D) 29, 9–15 (in Chinese with English abstract). Coleman, R.G., 1989. Continental growth of northwest China. Tectonics 8, 621–635. Dewey, J.F., 1988. Extensional collapse of orogens. Tectonics 7, 1123–1139.
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Please cite this article in press as: Li, P., et al. Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai. Journal of Asian Earth Sciences (2014), http://dx.doi.org/10.1016/j.jseaes.2014.11.004