Early Cretaceous gabbro–granite complex from central Inner Mongolia: Insights into initial rifting and crust–mantle interaction in the northern China–Mongolia basin–range tract
Early Cretaceous gabbro–granite complex from central Inner Mongolia: Insights into initial rifting and crust–mantle interaction in the northern China–Mongolia basin–range tract
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DOI：
10.1016/j.lithos.2018.12.010
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发表时间：
2019-01
期刊：
影响因子：
3.5
通讯作者：
Lingling Yuan;Xiaohui Zhang;Zhili Yang
中科院分区：
文献类型：
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作者：
Lingling Yuan;Xiaohui Zhang;Zhili Yang
同时代的高钾钙碱性钾玄质双峰式火成岩套房举行的关键，监测重要的地球动力学过程和壳幔相互作用的碰撞后，板内伸展设置。本文报道了中亚造山带东部、内蒙古中部、暴露较差的二连浩特盆地地区早白垩世一独特的辉长岩-花岗岩杂岩。镁铁质岩套包括小的正长辉长岩到二长闪长岩，而长英质岩套主要包括正长花岗岩和少量镁铁质到中等微粒包体。前者具有碱钙-碱性过渡特征，大离子亲石元素（LILEs）显著富集，高场强元素（HFSEs）弱-中度亏损，初始87 Sr/86 Sr比值较低（0.70486-0.70537），εNd（t）为正值（+2.1 − +2.6），锆石εHf（t）为正值（+2.3 − +9.0）。这些特征表明，它的起源于低程度熔融的角闪石轴承lherzitrium在岩石圈地幔已交代俯冲板片衍生流体。寄主花岗岩为镁质、碱钙质和过铝质。它们具有典型的岛弧长英质熔体的微量元素特征，初始87 Sr/86 Sr比值为0.70499 ~ 0.70593，εNd（t）为−0.1 ~+1.4，锆石εHf（t）为+4.8 ~+8.3，δ 18 O值为+4.53 ~+6.60‰。这些元素和同位素特征是一致的部分熔融的混合原岩组成的新底侵玄武岩材料和现存的老下地壳。二长岩包体为碱性，高度富集LILE，亏损HFSE，具有可变的全岩Sr单键Nd（ISr（t）= 0.70216-0.704678，εNd（t）= +0.2 − +1.8）和锆石Hf（εHf（t）= +0.9 − +7.1）同位素值。这些过渡成分与幔源镁铁质岩浆和壳源长英质岩浆之间的混合过程是相容的。早白垩世二连浩特辉长岩-花岗岩杂岩与区域性盆地形成的初始裂谷作用和蒙古-鄂霍次克洋的闭合作用在时间上是一致的，它不仅可以作为岩浆底侵作用与盆地形成的空间标志，而且还捕捉到了一个独特的快照壳幔相互作用在后造山伸展制度可能是由岩石圈滴和重力崩溃后，蒙古-鄂霍次克海峡
Coeval high-K calc-alkaline to shoshonitic bimodal igneous suites hold a key to monitoring important geodynamic processes and crust–mantle interactions within post-collisional to within-plate extensional settings. Here we report a unique early Cretaceous gabbro–granite complex from the poorly exposed Erenhot basin region of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB). The mafic suite includes small syenogabbro to monzodiorite stocks, while the felsic suite mainly comprises syenogranites with minor mafic to intermediate microgranular enclaves. The former exhibits a transitional character from alkali-calcic to alkalic, notable enrichment in large ion lithophile elements (LILEs) and weak to moderate depletion in high field strength elements (HFSEs), and possesses low initial87Sr/86Sr ratios (0.70486–0.70537), positive εNd(t) (+2.1 − +2.6) and zircon εHf(t) (+2.3 − +9.0) values. These features suggest its derivation from low-degree melting of amphibole-bearing lherzolites in the lithospheric mantle that had been metasomatized by subducting slab-derived fluids. The host granites are magnesian, alkali-calcic and peraluminous. They show typical trace elemental features of arc-related felsic melts, with initial87Sr/86Sr ratios of 0.70499 to 0.70593, εNd(t) of −0.1 to +1.4, zircon εHf(t) of +4.8 to +8.3 and δ18O values from +4.53 to +6.60‰. These elemental and isotopic traits are consistent with partial melts of a mixed protolith composed of newly-underplated basaltic materials and extant older lower crust. The monzonitic enclaves are alkalic, highly enriched in LILEs and depleted in HFSEs, with variable whole-rock Srsingle bondNd (ISr(t) = 0.70216–0.704678, εNd(t) = +0.2 − +1.8) and zircon Hf (εHf(t) = +0.9 − +7.1) isotopic values. These transitional compositions are compatible with hybridization processes between mantle-derived mafic magma and crust-derived felsic magma. Given its temporal coincidence with initial rifting in the regional basin formation and the closure of Mongol–Okhotsk ocean, Early Cretaceous Erenhot gabbro–granite complex could not only serve as spatial markers for relating magmatic underplating with basin formation, but also catch a unique snapshot into crust–mantle interactions within a post-orogenic extensional regime probably underpinned by lithospheric dripping and gravitational collapse after the Mongol–Okhotsk suturing.