Late Oligocene–Early Miocene initiation of shortening in the Southwestern Chinese Tian Shan: Implications for Neogene shortening rate variations
Late Oligocene–Early Miocene initiation of shortening in the Southwestern Chinese Tian Shan: Implications for Neogene shortening rate variations
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DOI：
10.1016/j.epsl.2006.03.048
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发表时间：
2006-07
影响因子：
5.3
通讯作者：
E. Sobel;Jie Chen;R. Heermance
中科院分区：
文献类型：
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作者：
E. Sobel;Jie Chen;R. Heermance
新生代天山是陆内造山带的一个突出实例。然而，关于与印度-亚洲碰撞有关的变形何时开始，以及山脉内的缩短如何随着时间的推移而划分，仍然存在重大争议。一种方法是研究大地测量研究所测量的现代缩短率，结合对整个范围内总缩短的估计，并向后外推。这种方法表明，范围建设的开始是ca。10 Ma [K.Y. Abdrakhmatov，S.A. Aldazhanov，B.H. Hager，M.W.汉堡，助教。Herring，K.B. Kalabaev，K.B.卡拉巴耶夫Makarov，P. Molnar，S.V. Panasyuk，M.T. Prilepin，R.E.赖林格，I.S. Sadybakasov，B.J. Souter，Y.A. Trapeznikov，V.Y. Tsurkov，A. V. Zubovich，从GPS测量的现今地壳变形率推断天山的相对近期构造，自然384（6608）（1996）450-453]。另一种方法是使用热年代学确定挖掘开始的年龄。我们提出了19个新的磷灰石裂变径迹（AFT）的结果，从中国西南部的一部分带，这一地区代表了第一个地区在晚第三纪期间，沿沿着一个断面约。东经76度。挖掘开始于渐新世-中新世边界（距今24 Ma），沿着Maidan和Muziduke逆冲断层，这两个断层界定了Kokshaal山脉的南侧。随后，变形传播约。喀什盆地边界逆冲断层（KBT）以南20 km处，其折返时间不早于18.9± 3.3Ma。三个碎屑AFT样品从上新世-更新世地层沉积约。再往南20公里处有裂变径迹颗粒年龄峰值，从20.9+7.0/− 5.3 Ma单调上升到15.9+5.4/− 4.0 Ma，滞后时间相当恒定，为16 ~ 18 Ma。这些年龄，结合结构数据，表明无论是上盘和下盘的KBT经历了一个新的插曲折返在最近的新生代。晚渐新世-中新世开始的显著折返与大地测量估计的10 Ma之间的差异表明天山经历了复杂的晚新生代缩短历史。假设目前的缩短率可以占新生代缩短的总量在10马，并实现缩短开始至少15万年前，我们得出结论，缩短率必须随着时间的推移而变化，可能在脉冲向南迁移事件，目前的速度可能不能反映平均速率，因为开始的范围隆起。
The Cenozoic Tian Shan is one of the preeminent examples of an intracontinental orogen. However, there remains a significant controversy over when deformation related to the India-Asia collision commenced and therefore how shortening within the mountains has been partitioned over time. One approach has been to look at the modern shortening rate as measured by geodetic studies, combined with estimates of the total shortening across the range and extrapolate backwards. This approach suggests that the onset of range construction was ca. 10 Ma [K.Y. Abdrakhmatov, S.A. Aldazhanov, B.H. Hager, M.W. Hamburger, T.A. Herring, K.B. Kalabaev, K.B. Kalabayev, V.I. Makarov, P. Molnar, S.V. Panasyuk, M.T. Prilepin, R.E. Reilinger, I.S. Sadybakasov, B.J. Souter, Y.A. Trapeznikov, V.Y. Tsurkov, A.V. Zubovich, Relatively recent construction of the Tien Shan inferred from GPS measurements of present-day crustal deformation rates, Nature 384 (6608) (1996) 450–453]. An alternate method is to determine the age of the onset of exhumation using thermochronology. We present 19 new apatite fission-track (AFT) results from the southwestern Chinese portion of the belt; this region represents the first area exhumed during the late Tertiary along a transect at ca. 76°E. Exhumation commenced at the Oligocene–Miocene boundary (∼ 24 Ma) along the Maidan and Muziduke thrusts, which bound the southern side of the Kokshaal range. Subsequently, deformation propagated ca. 20 km south to the Kashi basin-bounding thrust (KBT), which was exhumed by no earlier than 18.9±3.3 Ma. Three detrital AFT samples from Plio-Pleistocene strata deposited ca. 20 km farther south contain fission track grain age peaks that young monotonically upwards from 20.9+7.0/− 5.3 Ma to 15.9+5.4/− 4.0 Ma with a fairly constant lag time of 16 to 18 Ma. These ages, combined with structural data, suggest that both the hanging wall and the footwall of the KBT experienced a renewed episode of exhumation during the latest Cenozoic. The discrepancy between the Late Oligocene–Miocene initiation of significant exhumation shown herein and the 10 Ma initiation estimate from geodesy suggests that the Tian Shan has undergone a complex Late Cenozoic shortening history. Assuming that the present shortening rate could account for the total amount of Cenozoic shortening in 10 Ma and realizing that shortening initiated at least 15 Myr earlier, we conclude that the shortening rate must have varied over time, possibly in pulsed-southward migrating events, and that the present rate may not reflect the average rate since initiation of range uplift.