阿尔金断裂两侧构造单元的对比及岩石圈剪切机制
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摘要
中亚最大的阿尔金走滑断裂系构成了青藏高原的北部边界,阿尔金北缘断裂及阿尔金在行走滑断裂(阿尔金主断裂)所夹持的阿尔金地体自北往南由敦煌地块、北阿尔金加里东俯冲杂岩带、中阿尔金地块及南阿尔金加里东俯冲-碰撞杂岩带组成,研究表明这些单元分别可与阿尔金主断裂带东侧的阿拉善地块、北祁连俯冲杂岩带、中-南祁连地块及柴达木北缘加里东俯冲-碰撞杂岩带相对比。特别通过南阿尔金与柴达木北缘榴辉岩带的详细对比,发现它们具有相似的地质背景、产状、矿物组合、岩石地球化学、原岩特征、温度压力条件、退变质作用和围岩特征以及非常接近的峰期变质时代(500～503 Ma和495 Ma),可能构成了中国又一条被巨型走滑断裂所切割的高压-超高压变质带(?),并为阿尔金断裂带左行走滑400 km的确定提供了科学依据。天然地震探测剖面显示阿尔金主断裂由近直立低速低密度的物质组成,与低角度向南倾的阿尔金北缘断裂之间夹持由高速高密度组成的阿尔金地体。阿尔金北缘断裂与阿尔金主断裂在80km深度处交汇,并继续向南陡倾下插到150 km,反映出塔里木地块向南陆内俯冲于阿尔金山及柴达木盆地之下。代表上地幔物质剪切流动矢量的高强度各向异性,显示了剪切作用可抵达上地幔,阿尔金断裂的岩石圈剪切作用可能与塔里木地块往?
The Altun strike-slip fault is the largest strike-slip fault in Aisa and defines the northern boundary of the Qinghai-Tibet Plateau. The Altun terrane, bounded by the north Altun thrust fault and the Altun strike-slip fault on the south, consists of Dunhuang massif, northern Altun Caledonian subduction complex, central Altun massif and southern Altun subduction-collision complex from north to south. Our studies indicate that these tectonic units correspond to the Alxa block, northern Qilian subduction complex, central Qilian block and northern Qaidam subduction-collision zone respectively on the two sides of the Altun strike-slip fault. Especially, the eclogites in the southern Altun and northern Qaidam show strong similarities in geological setting, occurrence, mineral assemblage, geochemical and protolith feature, P-t condition of formation, retrograde metamorphism, associated country rock and almost consistent metamorphic age. This suggests the HP-UHP(?) metamorphic zone displaced by a large strike-slip fault be similar to the case of the Dabie - Sulu HP-UHP metamorphic zone which was truncated by the Tanlu sinistral strike-slip fault, and the offsets along the Altun sinistral strike-slip fault is about 400 km.A seismic tomographic section across the Altun Mountains , established by the natural earthquake experiment, indicates a steep low-velocity anomaly beneath and along the Altun strike-slip fault, and a high-velocity anomaly (implying dense material) beneath the Altun terrane located between the southern Altun strike-slip fault and the northern gently-dipping thrust fault. The two faults may meet at a depth of 80 km, then continue to underthrust steeply southward to 150 km, suggesting that Tarim block has been underthrusted southward beneath the Altun Mountains and the Qaidam block. The large magnitude of anisotropy represents the existence of shearing of upper mantle along Altun strike-slip fault , while the lithospheric shearing may be attributed to the southward subduction of the Tarim block.
The Altun strike-slip fault is the largest strike-slip fault in Aisa and defines the northern boundary of the Qinghai-Tibet Plateau. The Altun terrane, bounded by the north Altun thrust fault and the Altun strike-slip fault on the south, consists of Dunhuang massif, northern Altun Caledonian subduction complex, central Altun massif and southern Altun subduction-collision complex from north to south. Our studies indicate that these tectonic units correspond to the Alxa block, northern Qilian subduction complex, central Qilian block and northern Qaidam subduction-collision zone respectively on the two sides of the Altun strike-slip fault. Especially, the eclogites in the southern Altun and northern Qaidam show strong similarities in geological setting, occurrence, mineral assemblage, geochemical and protolith feature, P-t condition of formation, retrograde metamorphism, associated country rock and almost consistent metamorphic age. This suggests the HP-UHP(?) metamorphic zone displaced by a large strike-slip fault be similar to the case of the Dabie - Sulu HP-UHP metamorphic zone which was truncated by the Tanlu sinistral strike-slip fault, and the offsets along the Altun sinistral strike-slip fault is about 400 km.A seismic tomographic section across the Altun Mountains , established by the natural earthquake experiment, indicates a steep low-velocity anomaly beneath and along the Altun strike-slip fault, and a high-velocity anomaly (implying dense material) beneath the Altun terrane located between the southern Altun strike-slip fault and the northern gently-dipping thrust fault. The two faults may meet at a depth of 80 km, then continue to underthrust steeply southward to 150 km, suggesting that Tarim block has been underthrusted southward beneath the Altun Mountains and the Qaidam block. The large magnitude of anisotropy represents the existence of shearing of upper mantle along Altun strike-slip fault , while the lithospheric shearing may be attributed to the southward subduction of the Tarim block.
引文
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① 张建新.阿尔金构造带西段加里东期山根的初步研究.中国地质科学院博士论文,1998．
① 张建新.阿尔金构造带西段加里东期山根的初步研究.中国地质科学院博士论文,1998．
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② 张建新.阿尔金构造带西段加里东期山根的初步研究.中国地质科学院博士论文,1998．
① 张建新.阿尔金构造带西段加里东期山根的初步研究.中国地质科学院博士论文,1998．
① 张建新.阿尔金构造带西段加里东期山根的初步研究.中国地质科学院博士论文,1998．
1 Tapponnier P, Molnar P. Slip-line field theory and large-scale continental tectonics. Nature, 1976, 264: 319～324．
2 Peltzer G, Tapponnier P. Formation and evolution of strike-slip faults, rifts, and basins during the India-Asia collision: An experimental approach. Journal of Geophysical Research, 1988, 93 (12) : 15085～15117．
3 Avouac J P, Peltzer G. Kinematic model of active deformation in central Asia. from these de Doctorat de L'Universite Paris,Ⅶ., 1995．
4 许志琴,崔军文,张建新.大陆山链的变形构造动力学.北京:冶金工业出版社,1996．
5 郑剑东.阿尔金断裂带的几何学研究.中国区域地质,1991,36:54～59．
6 崔军文,邓晋福,唐哲民.青藏高原北缘变形构造动力学的一些新认识.中国地质科学院院报,1994,29:145～146．
7 国家地震局“阿尔金活动断裂带”课题组.阿尔金活动断裂带.北京:地震出版社,1992．
8 丁国瑜.阿尔金断裂的古地震与分段.第四纪研究,1995,2:97～106．
9 Zhou D, Graham S A. Extrusion of the Altyn Tagh wedge:A kinematic model for the Altyn Tagh and palinspastic reconstruction of north China. Geology, 1996, 24(5) : 427～430．
10 Wang E Q. Displacement and timing along the northern strand of the Altyn Tagh fault zone, northern Tibet. Earth Planet.Sci. Lett., 1997, 150: 55～64．
11 张建新,许志琴,崔军文.一个韧性转换挤压带的变形分解作用--以阿尔金断裂带东段为例.地质论评,1998,44(4) :348～356．
12 周勇,潘裕生.阿尔金断裂早期走滑运动方向及其活动时间探讨.地质论评,1999,45(1) :1～9．
13 车自成,刘良,刘洪福.阿尔金地区高压变质泥质岩石的发现及其产出环境.科学通报,1995,40(14) :1298～1300．
14 车自成,孙勇.阿尔金麻粒岩相杂岩的时代及塔里木盆地的基底.中国区域地质,1996,15(1) :51～57．
15 刘良,车自成,罗金海等.阿尔金山西段榴辉岩的确定及地质意义.科学通报,1996,41(14) :1485～1488．
16 刘良,车自成,王焰等.阿尔金茫崖地区早古生代蛇绿岩的Sm-Nd等时线年龄证据.科学通报,1998,43(8) :880～883．
17 郭召杰,张志诚,王建军.阿尔金北缘蛇绿岩的Sm-Nd等时线年龄及其大地构造意义.科学通报,1998,43(18) :1981～1984．
18 张建新,张泽明,许志琴,杨经绥,崔军文.阿尔金构造带西段榴辉岩的Sm-Nd及U-Pb年龄--阿尔金中加里东期山根存在的证据.科学通报,1999,44(10) :1109～1112．
19 张建新,张泽明,许志琴,杨经绥,崔军文.阿尔金西段孔兹岩系的发现及岩石学、同位素年代学初步研究.中国科生D辑,1999,29(3) :245～251．
20 Sobel E R, Arnaud N. A possible middle Paleozoic suture in the Altyn Tagh, NW China. Tectonics, 1999, 18 (1) : 64～74
21 葛肖虹,段吉业,李才等.阿尔金断裂与西北大地构造格局的新认识.见:肖庆辉等主编.地球科学进展.武汉:中国地质大学出版社,1996,9～18．
22 车自成,良,刘洪福,罗金海.阿尔金断裂系的组成及相关中生代含油气盆地的成因特征、中国区域地质,1998,17(4) :377～384．
23 崔军文,唐哲民,邓晋福,岳永军,孟令顺,余钦范等.阿尔金断褶系.北京:地质出版社,1999．
24 葛肖虹,张梅生,刘永江.阿尔金断裂研究的科学问题与研究思路.现代地质,1998,12(3) :295～301．
25 葛肖虹,刘俊来.北祁连造山带的形成与背景.地学前缘,1999,6(4) :223～230．
26 新疆维吾尔自治区地质矿产局.新疆维吾尔自治区区域地质志.北京:地质出版社,1993．
27 梅华林,于海峰等,甘肃北山地区首次发现榴辉岩和古元古花岗质岩石.科学通报,1988,43(19) :2103～2111．
28 潘桂棠,焦淑沛,徐耀荣,王培生,向天秀.阿尔金山新生代构造及造山性质.见;青藏高原地质文集(15) .北京:地质出版社,1984． 113～119．
29 刘良,车自成,王焰,罗金海,陈丹玲.阿尔金高压变质带的特征及其构造意义.岩石学报,1999,15(1) :57～64．
30 刘雪亚,王荃.龙首山古裂谷带及河西走廊的大地构造.中国地质科学院院报.1998,27～28:1～14．
31 夏林圻,夏祖春,徐学义.北祁连山的构造-火山-岩浆演化动力学.西北地质,1995,16:1～28．
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