Synchronous Oligocene–Miocene metamorphism of the Pamir and the north Himalaya driven by plate-scale dynamics
Synchronous Oligocene–Miocene metamorphism of the Pamir and the north Himalaya driven by plate-scale dynamics
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DOI：
10.1130/g34451.1
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发表时间：
2013-10
期刊：
影响因子：
5.8
通讯作者：
M. Stearns;B. Hacker;L. Ratschbacher;Jeffrey Lee;J. Cottle;A. Kylander‐Clark
中科院分区：
文献类型：
--
作者：
M. Stearns;B. Hacker;L. Ratschbacher;Jeffrey Lee;J. Cottle;A. Kylander‐Clark
帕米尔高原（中亚）和喜马拉雅山的片麻岩穹丘提供了印度-亚洲碰撞期间中深层地壳过程的关键数据。这些圆顶独居石的激光烧蚀分流电感耦合等离子体质谱 (LASS-ICP-MS) 数据产生了 U/Th-Pb 日期的时间记录和稀土元素 (REE) 丰度的岩石学记录。来自帕米尔高原的七个样本和来自喜马拉雅山北部片麻岩圆顶的六个样本得出了几乎相同的独居石年代，年代约为 100 年。 28-15 马。大多数独居石具有不变的重稀土元素 (HREE) 丰度；然而，两个样品具有较老的独居石，记录了 HREE 逐渐耗尽，而两个样品具有较年轻的独居石，记录了 HREE 逐渐富集。 HREE 的这些变化与石榴石丰度的增加（渐进变质作用）相一致，直到大约。 20 Ma，此后石榴石丰度下降。从重稀土元素消耗到富集的变化可能记录了从地壳增厚和加热到穹顶折返和冷却的转变。造山带边缘（喜马拉雅山）印度地壳穹顶内和造山带核心（帕米尔）亚洲地壳穹顶内同步巴罗夫变质作用的记录最好是通过板块尺度的驱动力而不是局部事件来解释的。我们认为，广泛的、同步的增厚是由板片断裂后印度俯冲的恢复引发的，然后由第二次板片撕裂事件终止——这两个事件都是从断层扫描中推断出的板块尺度事件。
Gneiss domes in the Pamir (Central Asia) and the Himalaya provide key data on mid- to deep-crustal processes operating during the India-Asia collision. Laser ablation split-stream inductively coupled plasma–mass spectrometry (LASS-ICP-MS) data from monazite in these domes yield a time record from U/Th-Pb dates and a petrologic record from rare earth element (REE) abundances. Seven samples from the Pamir and six samples from the north Himalayan gneiss domes yield almost identical monazite dates of ca. 28–15 Ma. Most monazite has invariant heavy REE (HREE) abundances; two samples, however, have older monazite that records progressive HREE depletion and two samples have younger monazite that records progressive HREE enrichment. These variations in HREE are compatible with increasing garnet abundance—prograde metamorphism— until ca. 20 Ma, and decreasing garnet abundance thereafter. The change from HREE depletion to enrichment may record a transition from crustal thickening and heating to dome exhumation and cooling. This documentation of synchronous Barrovian metamorphism within domes of Indian crust along the margin of the orogen (Himalaya) and within domes of Asian crust within the core of the orogen (Pamir) is best explained by a plate-scale driving force rather than by local events. We propose that widespread, synchronous thickening was initiated by the resumption of Indian subduction following slab breakoff and then terminated by a second slab-tearing event—both plate-scale events inferred from tomography.