Subducted slab-plume interaction traced by magnesium isotopes in the northern margin of the Tarim Large Igneous Province
Subducted slab-plume interaction traced by magnesium isotopes in the northern margin of the Tarim Large Igneous Province
复制标题
塔里木大火成岩省北缘镁同位素追踪的俯冲板片-地幔柱相互作用
DOI：
10.1016/j.epsl.2018.02.039
复制
发表时间：
2018-05-01
影响因子：
5.3
通讯作者：
Ke, Shan
中科院分区：
文献类型：
--
作者：
Cheng, Zhiguo;Zhang, Zhaochong;Ke, Shan
俯冲板块的合并可能解释大火成岩省（LIPS）的地球化学和同位素变化。然而，关于俯冲板块卷入岩浆的机制和过程，人们仍有很大的争议。本文报道了塔里木大火成岩省（TLIP）一套碱性和富铁岩石（包括玄武岩、基性-超基性层状侵入岩、辉绿岩脉和金伯利岩中的地幔包体）的高分辨率Mg同位素。我们观察到，玄武岩的δ Mg-26值范围为-0.29 ~ -0.45‰，基性-超基性层状侵入岩的Mg-26值范围为-0.31 ~ -0.42‰，辉绿岩脉的Mg-26值范围为-0.28 ~ -0.31‰，金伯利岩的辉石岩包体的Mg-26值范围为-0.29 ~ -0.44‰，通常比正常地幔源轻（-0.25‰+/- 0.04,2 SD）。在仔细排除其他可能性后，我们认为轻Mg同位素组成和高FeO含量应归因于再生沉积碳酸盐岩和辉石岩/榴辉岩的参与。此外，从玄武岩，通过层状侵入岩到辉绿岩脉，（Sr-87/Sr-86）；δ O-18（v-smow）和δ O-18（v-smow）值随着地幔部分熔融的进行而减小，而ε ((Nd))t和δ Mg-26值则随着地幔源中碳酸盐岩和辉石岩/榴辉岩组分的逐渐减少而增大。结合前人报道的塔里木盆地碳酸盐岩、云母岩和金伯利岩的Mg同位素特征，认为塔里木盆地存在两个明显的地幔域：1)玄武岩和基性-超基性层状侵入体的岩石圈地幔源，由方解石/白云岩和榴辉岩衍生的高si熔体改造，Sr-Nd-O和轻Mg同位素组成丰富；2)由Sr-Nd-O贫化和极轻的Mg同位素反映的烟柱源为碳酸盐、钠云母和金伯利岩，与菱镁矿或镁长石/钙钛矿有关。最终，我们的研究表明，俯冲板块可能对LIP的形成做出了重要贡献，并建立了板块构造与地幔柱之间的潜在联系。(C) 2018 Elsevier B.V.版权所有
Incorporation of subducted slabs may account for the geochemical and isotopic variations of large igneous provinces (LIPS). However, the mechanism and process by which subducted slabs are involved into magmas is still highly debated. Here, we report a set of high resolution Mg isotopes for a suite of alkaline and Fe-rich rocks (including basalts, mafic-ultramafic layered intrusions, diabase dykes and mantle xenoliths in the kimberlitic rocks) from Tarim Large Igneous Province (TLIP). We observed that delta Mg-26 values of basalts range from -0.29 to -0.45 parts per thousand, -0.31 to -0.42 parts per thousand for mafic-ultramafic layered intrusions, -0.28 to -0.31 parts per thousand for diabase dykes and -0.29 to -0.44 parts per thousand for pyroxenite xenoliths from the kimberlitic rocks, typically lighter than the normal mantle source (-0.25 parts per thousand +/- 0.04, 2 SD). After carefully precluding other possibilities, we propose that the light Mg isotopic compositions and high FeO contents should be ascribed to the involvement of recycled sedimentary carbonate rocks and pyroxenite/eclogite. Moreover, from basalts, through layered intrusions to diabase dykes, (Sr-87/Sr-86); values and delta O-18(v-smow) declined, whereas epsilon((Nd))t and delta Mg-26 values increased with progressive partial melting of mantle, indicating that components of carbonate rock and pyroxenite/eclogite in the mantle sources were waning over time. In combination with the previous reported Mg isotopes for carbonatite, nephelinite and kimberlitic rocks in TLIP, two distinct mantle domains are recognized for this province: 1) a lithospheric mantle source for basalts and mafic-ultramafic layered intrusions which were modified by calcite/dolomite and eclogite-derived high-Si melts, as evidenced by enriched Sr-Nd-O and light Mg isotopic compositions; 2) a plume source for carbonatite, nephelinite and kimberlitic rocks which were related to magnesite or periclase/perovskite involvement as reflected by depleted Sr-Nd-O and extremely light Mg isotopes. Ultimately, our study suggests that subducted slabs could make important contributions to LIP generation, and establishes a potential linkage between plate tectonics and mantle plume. (C) 2018 Elsevier B.V. All rights reserved.