Peneplain formation in southern Tibet predates the India-Asia collision and plateau uplift
Peneplain formation in southern Tibet predates the India-Asia collision and plateau uplift
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DOI：
10.1130/g32069.1
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发表时间：
2011-10-01
期刊：
影响因子：
5.8
通讯作者：
Frei, Dirk
中科院分区：
文献类型：
--
作者：
Hetzel, Ralf;Dunkl, Istvan;Frei, Dirk
y。研究的准平原位于拉萨地块北部，海拔约5300 m，由白垩纪花岗岩类和侏罗纪变质沉积物雕刻而成。基于磷灰石和锆石的(U-Th)/He年龄和磷灰石裂变径迹数据的热模拟表明，花岗岩类在约70 ~ 55 Ma之间冷却和掘出，随后掘出速率迅速下降，接近300 m/m.y。与10米/米相似。约55至48毫安之间。从那以后，准平原一直是一个相当稳定的地貌特征，当地和整个流域的侵蚀率较低，为6-11米/立方米。11-16米/米。，分别来源于基岩、砾石和河流沉积物中宇宙成因的Be-10浓度。大约50万年结束的长期侵蚀和夷平阶段从准平原地区移走了3-6公里的岩石，可能是由横向迁移的河流完成的。拉萨地块北部缺乏等效沉积物，而拉萨地块南部存在区域不整合，表明河流将这些物质输送到海洋。这意味着侵蚀和准平原在低海拔进行，直到印度与亚洲的碰撞导致地壳增厚、表面隆起和准平原的长期保存。
The uplift history of Tibet is crucial for understanding the geodynamic and paleoclimatologic evolution of Asia; however, it remains controversial whether Tibet attained its high elevation before or after India collided with Asia similar to 50 m.y. ago. Here we use thermochronologic and cosmogenic nuclide data from a large bedrock peneplain in southern Tibet to shed light on the timing of the uplift. The studied peneplain, which was carved into Cretaceous granitoids and Jurassic metasediments, is located in the northern Lhasa block at an altitude of similar to 5300 m. Thermal modeling based on (U-Th)/He ages of apatite and zircon, and apatite fission track data, indicate cooling and exhumation of the granitoids between ca. 70 and ca. 55 Ma, followed by a rapid decline in exhumation rate from similar to 300 m/m.y. to similar to 10 m/m.y. between ca. 55 and ca. 48 Ma. Since then, the peneplain has been a rather stable geomorphic feature, as indicated by low local and catchment-wide erosion rates of 6-11 m/m.y. and 11-16 m/m.y., respectively, which were derived from cosmogenic Be-10 concentrations in bedrock, grus, and stream sediment. The prolonged phase of erosion and planation that ended ca. 50 Ma removed 3-6 km of rock from the peneplain region, likely accomplished by laterally migrating rivers. The lack of equivalent sediments in the northern Lhasa block and the presence of a regional unconformity in the southern Lhasa block indicate that the rivers delivered this material to the ocean. This implies that erosion and peneplanation proceeded at low elevation until India's collision with Asia induced crustal thickening, surface uplift, and long-term preservation of the peneplain.