Geochronology and petrology of the Early Carboniferous Misho Mafic Complex (NW Iran), and implications for the melt evolution of Paleo-Tethyan rifting in Western Cimmeria
Geochronology and petrology of the Early Carboniferous Misho Mafic Complex (NW Iran), and implications for the melt evolution of Paleo-Tethyan rifting in Western Cimmeria
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DOI：
10.1016/j.lithos.2013.01.008
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发表时间：
2013-03
期刊：
影响因子：
3.5
通讯作者：
E. Saccani;Z. Azimzadeh;Y. Dilek;A. Jahangiri
中科院分区：
文献类型：
--
作者：
E. Saccani;Z. Azimzadeh;Y. Dilek;A. Jahangiri
本文报道了来自伊朗西北部Misho基蒂克杂岩的新的岩石学、地球化学和年代学数据，该杂岩代表了古特提斯西西梅里亚域的一个重要组成部分。三朔基性杂岩（MMC）主要由丰富的玄武岩岩脉和上覆的玄武岩片状岩脉杂岩组成。辉长岩侵入前寒武纪大陆基底，代表冈瓦纳北缘。浅辉长岩岩脉的U-Pb锆石年龄显示，该岩脉的火成岩侵位年龄为356.7±3.4Ma（早石炭世）。辉长岩和玄武岩岩脉由(1)具有正常洋中脊玄武岩（N-MORB）亲和力的岩石亚群和(2)具有羽状MORB （P-MORB）亲和力的岩石亚群所代表。这些岩石亚群是同时期的。N-MORB岩石具有几乎平坦的N-MORB归一化不相容元素模式，具有较低的Th/Yb、Ta/Yb、Zr/Y比值和较高的Zr/Nb比值。P-MORB岩石具有明显的obb型微量元素特征，N-MORB组成中Th、Ta、Nb和轻稀土元素（LREE）富集，Th/Yb、Ta/Yb、Zr/Y比值较高，Zr/Nb比值较低。岩石成因模拟表明，N-MORB型岩石是由贫MORB型地幔（DMM）源~13%的部分熔融形成的，而P-MORB型岩石是由贫MORB型地幔（DMM）源~ 4-6%的部分熔融由不同比例的oib型（羽状）富集组分交代形成的。n - morb和p - morb的地幔融化似乎都是从石榴石相地幔深部开始的，然后转移到尖晶石相地幔的浅层，在那里它经历了更高程度的融化。MMC是枯竭的morb型软流层和羽状物质相互作用的产物。它的镁铁质-超镁铁质岩石代表了早石炭纪的岩浆活动，在冈瓦纳大陆北部边缘的大陆分裂期间发展起来，导致了古特提斯的开放，这最初是由地幔柱引发的。这一模式与有充分文献记载的东亚中东部古特提斯边缘晚泥盆世-早石炭世地幔柱活动相一致，表明古特提斯的初始裂谷漂移构造在区域尺度上受到与地幔柱相关的岩浆活动和岩石圈减弱的强烈影响。
We report new petrological, geochemical and geochronological data from the Misho Mafic Complex (NW Iran), which represents a significant component of the West Cimmerian domain in Paleo-Tethys. The Misho Mafic Complex (MMC) mainly consists of gabbros crosscut by abundant basaltic dykes and the overlying basaltic sheeted dyke complex. Gabbros are intrusive into the Precambrian continental basement representing the northern margin of Gondwana. The U–Pb zircon age of a leucogabbro dyke reveals that the igneous emplacement age of the MMC is 356.7±3.4Ma (Early Carboniferous). The gabbros and basaltic dykes are represented by (1) a subgroup of rocks showing normal mid-ocean ridge basalt (N-MORB) affinity, and (2) another subgroup of rocks displaying plume-type MORB (P-MORB) affinity. These subgroups of rocks are coeval. The N-MORB rocks have almost flat N-MORB normalized incompatible element patterns, low Th/Yb, Ta/Yb, Zr/Y ratios, and high Zr/Nb ratios. The P-MORB rocks show significant OIB-type trace element signatures, such as enrichments in Th, Ta, Nb and light rare earth elements (LREE) with respect to N-MORB composition, high Th/Yb, Ta/Yb, Zr/Y ratios, and low Zr/Nb ratios. Petrogenetic modeling suggests that N-MORB rocks were generated by ~13% partial melting of a depleted MORB mantle (DMM) source, whereas P-MORB rocks were generated by ~4–6% partial melting of a DMM source metasomatized by variable proportions of OIB-type (plume-type) enriched components. The mantle melting for both N-MORBs and P-MORBs appears to have started initially deep in the garnet-facies mantle, and then shifted to shallow levels in the spinel-facies mantle where it experienced higher degrees of melting. The MMC collectively formed as a product of interaction between a depleted MORB-type asthenosphere and plume-type material. Its mafic–ultramafic rocks represent an early Carboniferous magmatic event developed during the continental break-up of the northern edge of Gondwana that led to the opening of Paleo-Tethys, that was originally triggered by a mantle plume. This model is consistent with well-documented late Devonian–early Carboniferous mantle plume activity to the east, along the Paleo-Tethys margins in central-eastern Asia, and suggests that the initial rift-drift tectonics of Paleo-Tethys was strongly affected by plume-related magmatism and associated lithospheric weakening at a regional scale.