Building the Pamir‐Tibetan Plateau—Crustal stacking, extensional collapse, and lateral extrusion in the Central Pamir: 1. Geometry and kinematics
Building the Pamir‐Tibetan Plateau—Crustal stacking, extensional collapse, and lateral extrusion in the Central Pamir: 1. Geometry and kinematics
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DOI：
10.1002/2016tc004293
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发表时间：
2017-03
期刊：
影响因子：
4.2
通讯作者：
D. Rutte;L. Ratschbacher;S. Schneider;K. Stübner;M. Stearns;M. A. Gulzar;B. Hacker
中科院分区：
文献类型：
--
作者：
D. Rutte;L. Ratschbacher;S. Schneider;K. Stübner;M. Stearns;M. A. Gulzar;B. Hacker
暴露在帕米尔的亚洲深部地壳允许确定印度-亚洲碰撞期间约30 km地壳剖面的缩短、伸展和侧向挤压的数量、顺序和相互作用。在帕米尔高原中部，片麻岩穹丘及其上盘记录了古近纪时厚7-10公里的上地壳地层的三倍;地壳总厚度可能达到90公里。两个逆冲岩席，分别由寒武-奥陶纪、石炭纪至古近纪地层组成，横跨穹隆。角闪岩相变质岩，在具有圆顶规模波长的形褶皱推覆体外部，相当于较低级岩石。E-W拉伸与顶部到N的叠瓦和折叠同时发生。在约22-12 Ma，分叉（从上到北和从上到南）的正向剪切带将结晶岩挖出;大部分伸展发生在沿着北方穹隆边缘。缩短在~12 Ma时恢复，相反方向的逆冲推覆和褶皱集中于沿着穹隆边缘。在帕米尔中部和南部的整个构造过程中，主要的~ N-S缩短与~ E-W伸展相互作用，沿着大多数右旋剪切/断层带。在新近纪，剪切力主要集中在穹隆南部的沿着一条右向的扳手走廊。我们将古近纪缩短解释为帕米尔-青藏高原的增厚和向北生长，将短暂的中新世地壳伸展解释为重力调整，即，印度板块断裂的加厚亚洲地壳的坍塌。古近纪同会聚侧向挤压使印度-亚洲碰撞以西的阿富汗兴都库什地壳增厚，中新世-近代右旋剪切和~ E-W向伸展使帕米尔高原塌陷到塔吉克凹陷。
Asian deep crust exposed in the Pamir permits determination of the amount, sequence, and interaction of shortening, extension, and lateral extrusion over ~30 km of crustal section during the India‐Asia collision. In the Central Pamir, gneiss domes and their hanging walls record Paleogene tripling of the 7–10 km thick Phanerozoic upper crustal strata; total crustal thickness may have amounted to 90 km. Two thrust sheets, comprising Cambro‐Ordovician, respectively, Carboniferous to Paleogene strata, straddle the domes. Amphibolite‐facies metamorphic rocks within the domes—equivalent to lower grade rocks outside the domes—form fold nappes with dome‐scale wavelengths. E‐W stretching occurred contemporaneously with top‐to‐ ~ N imbrication and folding. At ~22–12 Ma, bivergent (top‐to‐N and top‐to‐S), normal‐sense shear zones exhumed the crystalline rocks; most of the extension occurred along the northern dome margins. Shortening resumed at ~12 Ma with opposite‐sense thrusting and folding focused along the dome margins. Throughout the building of the Central and South Pamir, dominant ~N‐S shortening interacted with ~E‐W extension along mostly dextral shear/fault zones. In the Neogene, shear is concentrated along a dextral wrench corridor south of the domes. We interpret the Paleogene shortening to record thickening and northward growth of the Pamir‐Tibetan Plateau and short‐lived Miocene crustal extension as gravitational adjustment, i.e., collapse, of the thickened Asian crust to Indian slab breakoff. Synconvergent Paleogene lateral extrusion thickened the Afghan Hindu Kush crust west of the India‐Asia collision, and the Miocene‐Recent dextral shear and ~E‐W extension have accommodated collapse of the Pamir Plateau into the Tajik depression.