Cretaceous high-potassium intrusive rocks in the Yueshan-Hongzhen area of east China: Adakites in an extensional tectonic regime within a continent
Cretaceous high-potassium intrusive rocks in the Yueshan-Hongzhen area of east China: Adakites in an extensional tectonic regime within a continent
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DOI：
10.2343/geochemj.38.417
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发表时间：
2004-10
影响因子：
0.8
通讯作者：
Qiang Wang;Ji‐Feng Xu;Zhenhua Zhao;Z. Bao;Wei Xu;Xiaolin Xiong
中科院分区：
文献类型：
--
作者：
Qiang Wang;Ji‐Feng Xu;Zhenhua Zhao;Z. Bao;Wei Xu;Xiaolin Xiong
埃达克岩通常与俯冲带（即，在会聚的板块边缘）。本文报道了中国东部月山-洪镇地区早白垩世高钾埃达克质侵入岩的地球化学和同位素资料。根据岩石学和地球化学特征，将这些埃达克质侵入岩分为两类。红镇埃达克质花岗岩具有高SiO_2（69-75%）、高K_2O/Na_2O（>1.0）、低MgO（或Mg#）、低Ni和V含量、低eNd（t）（-17.01 <$-18.13）和高（87 Sr/86 Sr）i（0.7071 <$0.7072）的特征。另一组（月山和总铺埃达克岩）的特征是SiO_2含量较低（58-67%），K_2O/Na_2O比值较低（1.2GPa），其源区残留石榴子石+辉石。两组埃达克质岩石均具有较高的La/Yb和Sr/Y比值，表明早白垩世月山-洪镇地区埃达克质岩浆生成时地壳厚度超过40 km。月山-洪镇地区现今地壳厚度仅为1.31 km，自早白垩世以来至少减薄了1.10 km。月山和总铺埃达克质岩石的MgO、Ni和V值较高，表明埃达克质岩浆与地幔岩石发生了相互作用，可能与下地壳拆沉作用同时发生。
Adakites are generally associated with subduction zones (i.e., at convergent plate margins). This paper reports geochemical and isotopic data for early Cretaceous high-potassium adakitic intrusive rocks in the Yueshan-Hongzhen area of east China, which occur in an extensional tectonic regime within a continent. Based on petrology and geochemistry, these adakitic intrusive rocks are classified into two groups. One group (the Hongzhen adakitic granites) is characterized by high SiO2 (69-75%) contents and K2O/Na2O (>1.0), low MgO (or Mg#) values, Ni and V concentrations, low eNd(t) (-17.01∼-18.13), and high (87Sr/86Sr)i (0.7071∼0.7072). The other group (the Yueshan and Zongpu adakitic rocks) is characterized by relatively low SiO2 (58-67%) contents and K2O/Na2O ( 1.2 GPa, leaving residual garnet + pyroxene in their sources. Both groups of adakitic rocks have high La/Yb and Sr/Y, indicating that the crustal thickness in the Yueshan-Hongzhen area exceeded 40 km when the adakitic magmas were generated in the early Cretaceous. The present thickness of the crust in the Yueshan-Hongzhen area is only ∼31 km, and therefore the crust appears to have been thinned by at least ∼10 km since the early Cretaceous. The relatively high MgO, Ni, and V values of the Yueshan and Zongpu adakitic rocks suggest that adakitic magmas interacted with mantle rocks, possibly concurrently with delamination of the lower crust.