Geochronology and geochemistry of the Early Cretaceous Jigongshan and Qijianfeng batholiths in the Tongbai orogen, central China: implications for lower crustal delamination
Geochronology and geochemistry of the Early Cretaceous Jigongshan and Qijianfeng batholiths in the Tongbai orogen, central China: implications for lower crustal delamination
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中国中部桐柏造山带早白垩世鸡公山和七尖峰岩基的年代学和地球化学：对下地壳拆沉的意义
DOI：
10.1007/s00531-012-0849-1
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发表时间：
2013-06
影响因子：
2.3
通讯作者：
Zhang Chao
中科院分区：
文献类型：
--
作者：
Zhang Jinyang;Ma Changqian;Li Jianwei;She Zhenbing;Zhang Chao
桐柏造山带鸡公山和七尖峰岩体主要由斑状角闪黑云二长花岗岩、黑云二长花岗岩和黑云正长花岗岩组成，受层状脉、闪长脉和正长花岗岩脉的侵入。镁铁质微粒包体常产于角闪黑云二长花岗岩中，而钠长石包体则产于黑云二长花岗岩中。这两个岩基的锆石U-Pb年龄都在约1000 ~ 10000 μ m之间。139 ~ 120 Ma，表明其侵位时代为早白垩世。角闪黑云二长花岗岩具有较高的Sr/Y和（La/Yb）N比值，缺乏Eu异常，MgO和Ni含量较低，Na_2 O> K_2 O的埃达克质亲合性。它的化学成分，结合丰富的Sr-Nd同位素特征，建议形成的镁铁质岩石在加厚的下地壳脱水熔融。这种增厚的地壳是二叠纪-三叠纪华北陆块与华南陆块俯冲碰撞的结果，并一直持续到早白垩世。黑云母二长花岗岩和黑云母正长花岗岩具有低Al 2 O3、CaO和Sr含量，低Rb/Sr、FeOt/MgO和（Na 2 O + K2 O）/CaO比值，HREE配分模式平坦，具中-弱Eu异常。它们是地壳物质在相对低压下部分熔融而形成的。地壳不同层次的部分熔融可能大大促进了地壳的机械弱化。在Harker图解上，闪长岩脉和层状岩脉中SiO2与主量或微量元素呈线性关系，其中两个层状岩样品含有标准霞石和橄榄石。这些岩石具有较高的La/Yb和Dy/Yb比值，二者均与Yb含量呈协变关系。它们起源于相对较深的岩石圈地幔，并经历了橄榄石+单斜辉石+磷灰石+ Fe-Ti氧化物的分馏作用。岩石圈地幔广泛的部分熔融表明在这一水平相对较高的温度。我们认为，埃达克质岩浆的存在，增厚，但削弱地壳和岩石圈地幔的高温在桐柏造山带早白垩世的下地壳拆沉。
The Jigongshan and Qijianfeng batholiths in the Tongbai orogen consist mainly of porphyritic hornblende-biotite monzogranite, biotite monzogranite, and biotite syenogranite, which are variably intruded by lamprophyre, diorite, and syenogranite dykes. Mafic microgranular enclaves commonly occur in the hornblende-biotite monzogranite, whereas surmicaceous enclaves are found in the biotite monzogranite. Both batholiths have zircon U–Pb ages ranging from ca. 139 to 120 Ma, indicating their emplacement in the Early Cretaceous. The hornblende-biotite monzogranite has an adakitic affinity marked by relatively high Sr/Y and (La/Yb)Nratios, lack of Eu anomalies, low MgO and Ni contents, and Na2O > K2O. Its chemical compositions, combined with enriched Sr–Nd isotopic signatures, suggest formation by dehydration melting of mafic rocks in a thickened lower crust. This thickened crust resulted from the Permo-Triassic subduction-collision between the North China and South China blocks and persisted until the Early Cretaceous. The biotite monzogranite and biotite syenogranite have low Al2O3, CaO, and Sr contents, low Rb/Sr, FeOt/MgO, and (Na2O + K2O)/CaO ratios, and flat HREE patterns with moderate to weak Eu anomalies. They were produced by partial melting of crustal materials under relatively low pressure. Partial melting at different crustal levels could have significantly contributed to mechanical weakening of the crust. The diorite and lamprophyre dykes show linear trends between SiO2and major or trace elements on Harker diagrams, with two lamprophyre samples containing normative nepheline and olivine. These rocks have high La/Yb and Dy/Yb ratios, both displaying co-variation with contents of Yb. They were originated from relatively deep lithospheric mantle followed by fractionation of olivine + clinopyroxene + apatite + Fe–Ti oxides. Extensive partial melting in the lithospheric mantle indicates relatively high temperatures at this level. We suggest that the presence of adakitic magmas, thickened but weakened crust and high temperatures in the lithosphere mantle point to lower crustal delamination in the Early Cretaceous in the Tongbai orogen.
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影响因子：
3.5
作者：
J. Liégeois;J. Navez;J. Hertogen;R. Black
通讯作者：
J. Liégeois;J. Navez;J. Hertogen;R. Black
影响因子：
3.5
作者：
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影响因子：
3.1
作者：
Xiang, Biwei;Wang, Yongsheng;Zhu, Guang;Jiang, Dazhi
通讯作者：
Jiang, Dazhi
影响因子：
3.5
作者：
Hongfei Zhang;Z. Zhong;Shan Gao;Ben-ren Zhang;Li Zhang;Shenghong Hu;Q. Hou
通讯作者：
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影响因子：
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作者：
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通讯作者：
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