Andesitic crustal growth via mélange partial melting: Evidence from Early Cretaceous arc dioritic/andesitic rocks in southern Qiangtang, central Tibet
Andesitic crustal growth via mélange partial melting: Evidence from Early Cretaceous arc dioritic/andesitic rocks in southern Qiangtang, central Tibet
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DOI：
10.1002/2016gc006248
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发表时间：
2016-05
期刊：
影响因子：
3.7
通讯作者：
Lu‐Lu Hao;Qiang Wang;D. Wyman;Quan Ou;Wei Dan;Zi-qi Jiang;Jin-Hui Yang;Jie Li;X. Long
中科院分区：
文献类型：
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作者：
Lu‐Lu Hao;Qiang Wang;D. Wyman;Quan Ou;Wei Dan;Zi-qi Jiang;Jin-Hui Yang;Jie Li;X. Long
破译安山岩/闪长岩的岩石成因是理解大陆地壳形成的基础。闪长质岩石以大离子型亲石元素Pb、轻稀土元素为主，而高场强元素富集，εNd(t)值在- 0.01 ~ - 3.31之间变化，初始87Sr/86Sr同位素比值为0.7053 ~ 0.7062。岩浆锆石Hf‐O同位素组成变化较大（εHf(t) =−5.3 ~ +3.6,δ18O = +7.3 ~ +9.5‰）。结合羌塘南部的当代安山岩熔岩，我们认为该地区的中间岩浆岩很可能是由俯冲带的部分熔融形成的，该俯冲带是俯冲通道中沿俯冲板块和上覆地幔楔之间的界面形成的中洋脊玄武岩（MORBs）、沉积物和地幔楔橄榄岩的混合物。早白垩世班公-怒江洋板块北俯冲回滚引起的软流圈上升流和热角流引发了马文兰底辟的融化。羌塘南部早白垩世中岩浆岩具有整体似陆壳的安山岩组成。因此，msamuange的部分熔融为大陆弧中安山岩岩浆的生成和地壳生长的“安山岩模式”提供了重要支撑。
Deciphering the petrogenesis of andesitic/dioritic rocks is fundamental to understanding the formation of the continental crust. Here we present detailed petrology, geochronology, major and trace element, Sr–Nd–Hf–O isotope data for the Early Cretaceous (∼122 Ma) dioritic rocks in the Bizha area in southern Qiangtang, Tibet. The dioritic rocks are characterized by large ion lithophile elements, Pb, and light rare earth elements but depletion of high field strength elements with slightly enriched and variable εNd(t) values of −0.01 to −3.31 and initial 87Sr/86Sr isotopic ratios of 0.7053–0.7062. They also have variable magmatic zircon Hf‐O isotope compositions (εHf(t) = −5.3 to +3.6 and δ18O = +7.3 to +9.5 ‰). Combined with contemporary andesitic lavas in southern Qiangtang, we suggest that the intermediate magmatic rocks in this area were most probably derived by partial melting of a subduction mélange, which is a mixture of mid‐oceanic ridge basalts (MORBs), sediments, and mantle wedge peridotites, formed along the interface between the subducted slab and the overlying mantle wedge in a subduction channel before ∼124 Ma. The mélange diapir melting was triggered by the asthenospheric upwelling and hot corner flow caused by roll‐back of the northward subducted Bangong‐Nujiang oceanic slab during the Early Cretaceous. The Early Cretaceous intermediate magmatic rocks in southern Qiangtang have an overall continental crust‐like andesitic composition. Therefore, partial melting of mélange provides an important support for the generation of andesitic magmas in continental arcs and the “andesite model” for crustal growth.