Late Cenozoic magmatic inflation, crustal thickening, and >2 km of surface uplift in central Tibet
Late Cenozoic magmatic inflation, crustal thickening, and >2 km of surface uplift in central Tibet
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西藏中部晚新生代岩浆膨胀、地壳增厚和地表隆升超过2公里
DOI：
10.1130/g39699.1
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发表时间：
2018-01-01
期刊：
影响因子：
5.8
通讯作者：
Kang, Zhi-Qiang
中科院分区：
文献类型：
--
作者：
Chen, Jian-Lin;Yin, An;Kang, Zhi-Qiang
从西藏中部晚始新世到上新世火山岩中获得的高La/Yb值（>15-20）表明源区位于较厚（>35 km）的地壳中。与较低的古近纪 La/Yb 值相比，较高的新近纪 La/Yb 值需要持续地壳增厚，因为 La/Yb 值与地壳厚度成正比。虽然古近纪高La/Yb值可以用同时期逆冲作用来解释，但这种机制无法解释新近纪高La/Yb值，因为西藏中部被未变形的平地早中新世地层覆盖。在这里，我们将新生代火山地球化学的时间变化与西藏中部的区域地质联系起来，西藏中部是更大的始新世-渐新世冲断带和相关前陆盆地的一部分。古近纪前陆盆地被昆仑断裂分为南部（可可西里）和北部（柴达木）两个亚盆地。 25-20马。两个次盆地形成时的海拔高度相似，但南部盆地约 5 公里，比北部盆地约 2.8 公里高 > 2 公里。由于南部盆地和古近纪冲断带与新近纪火山活动和高 La/Yb 值有关，我们认为两个盆地之间的高程差异是由地幔熔融引起的 >15 km 的岩浆膨胀引起的。岩浆膨胀的幅度与青藏高原中部构造增厚的程度相当，凸显了同碰撞地幔熔融及其诱发的岩浆膨胀在构造增厚的青藏高原地壳中的重要且经常被忽视的作用。
The high values of La/Yb (>15-20) obtained from late Eocene to Pliocene volcanic rocks of central Tibet indicate that source regions were in a thickened (>35 km) crust. The higher Neogene La/Yb values compared to lower Paleogene La/Yb values required continuous crustal thickening, as La/Yb values are proportional to crustal thickness. Although the Paleogene high La/Yb values can be explained by coeval thrusting, this mechanism is unable explain the Neogene higher La/Yb values because central Tibet is covered by undeformed flat-lying early Miocene strata. Here we correlate the temporal variation of Cenozoic volcanic geochemistry with the regional geology of central Tibet, which was part of a larger Eocene-Oligocene thrust belt and the related foreland basin. The Paleogene foreland basin was partitioned into the southern (Hoh Xil) and northern (Qaidam) subbasins by the Kunlun fault ca. 25-20 Ma. The two subbasins were at similar elevations at the time of their formation, but the southern basin, at similar to 5 km, is >2 km higher than the northern basin at similar to 2.8 km. Because the southern basin and the Paleogene thrust belt have been associated with Neogene volcanism and high La/Yb values, we suggest that the elevation difference between the two basins was induced by >15 km of magmatic inflation sourced from mantle melting. The magnitude of magmatic inflation is comparable to that of tectonic thickening in central Tibet, highlighting the important and often neglected role of syncollisional mantle melting and its induced magmatic inflation in constructing the thickened Tibetan crust.