New paleomagnetic constraints on central Asian kinematics: Displacement along the Altyn Tagh fault and rotation of the Qaidam Basin
New paleomagnetic constraints on central Asian kinematics: Displacement along the Altyn Tagh fault and rotation of the Qaidam Basin
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DOI：
10.1029/2001tc901030
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发表时间：
2002-10
期刊：
影响因子：
4.2
通讯作者：
Yan Chen;S. Gilder;Nadir Halim;J. Cogné;V. Courtillot
中科院分区：
文献类型：
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作者：
Yan Chen;S. Gilder;Nadir Halim;J. Cogné;V. Courtillot
为了更好地了解印度-亚洲碰撞影响下的中亚构造演化，我们对阿尔金断裂带、柴达木盆地、塔里木盆地和青藏高原沿着106个测点的1500个岩心进行了古地磁研究。样品主要采集自侏罗系至新近系的粉砂岩和砂岩。在大多数情况下，分步热退磁解除了磁铁矿和赤铁矿携带的低温和高温组分的阻塞。低温分量是北向和下向的，靠近现代地磁场。13个年龄/地点组中有10个的高温成分通过了折叠和/或反转测试，可能代表了原始的反射磁化。这10个总体平均方向显示了一种复杂的垂直轴块体旋转模式，与柴达木盆地顺时针旋转和阿尔金断裂伴随左旋滑动的构造模式相一致。十个地点中有两个明显逆时针旋转;它们邻近阿尔金断裂带，这与沿着该断裂带发生左旋走滑运动的观点一致。断层东端附近逆时针旋转的年龄被测得小于19 Ma。柴达木盆地内分布广泛的三个地区相对于华北地块、塔里木和欧亚大陆表现出相似的显著的顺时针旋转，约为20°。这三个值的平均值被认为代表了柴达木的总旋转。由于最年轻的顺时针旋转岩石是渐新世，柴达木盆地旋转的主要阶段，因此阿尔金断裂的剪切发生在渐新世末（124 Ma）之后或附近。柴达木盆地晚第三纪上部地层旋转不明显，古地磁方法无法分辨晚第三纪上部（1.5Ma）以来的构造变形。假设柴达木盆地相对于塔里木盆地顺时针旋转20° ± 5°，阿尔金断裂自24 Ma以来的最大左旋位移量为500 ± 130 km。
In order to better understand the tectonic evolution of central Asia under the influence of the India‐Asia collision, we carried out a paleomagnetic study of 1500 cores from 106 sites along the Altyn Tagh fault, in the Qaidam and Tarim basins, and on the Tibetan plateau. Samples were mainly collected from Jurassic to Neogene siltstones and sandstones. In most cases stepwise thermal demagnetization unblocks low and high temperature components carried by magnetite and hematite. Low temperature components are north and down directed and lie close to the recent geomagnetic field. High temperature components from 10 of 13 age/locality groups pass fold and/or reversal tests and likely represent primary remanent magnetizations. The ten overall mean directions display a complex pattern of vertical‐axis block rotations that are compatible with a tectonic model of clockwise rotation of the Qaidam Basin and concomitant left‐lateral slip on the Altyn Tagh fault. Two of the ten localities are rotated significantly counterclockwise; they lie adjacent to the Altyn Tagh fault zone, consistent with the idea that left‐lateral strike‐slip motion occurred along it. The age of counterclockwise rotation near the eastern extremity of the fault was dated as younger than 19 Ma. Three widely spread areas within the Qaidam Basin exhibit similar and significant clockwise rotations, on the order of 20°, with respect to the North China Block, Tarim and Eurasia. The mean of the three values is thought to represent the total rotation of Qaidam. Because the youngest rocks displaying clockwise rotations are Oligocene, the main phase of Qaidam Basin rotation, and hence shear on the Altyn Tagh fault, took place after or near the end of the Oligocene (∼24 Ma). Upper Neogene strata located on the Qaidam Basin are not significantly rotated, thus tectonic deformation acting since the Upper Neogene (∼5 Ma) is not resolvable by paleomagnetic methods. Given a 20° ± 5° clockwise rotation of the Qaidam Basin with respect to the Tarim Basin, the maximum left‐lateral displacement on the Altyn Tagh fault since 24 Ma is 500 ± 130 km.