Objective Though the Central Asian Orogenic Belt (CAOB) is characterized by widespread Phanerozoic crustal growth,there is little juvenile crust documented in its southeastern segment,northern margin of the North Chin...Objective Though the Central Asian Orogenic Belt (CAOB) is characterized by widespread Phanerozoic crustal growth,there is little juvenile crust documented in its southeastern segment,northern margin of the North China Craton(NCC)(Zhang et al,2007,2009).Late Carboniferous Dongwanzi ultramafic-mafic cumulate complex occurs in northern margin of the NCC and is intruded by a syenite with depleted Sr-Nd isotopes (Ma et al.,2014).However,the age and petrogenesis of this syenite is poorly constrained.In this study,we present new petrological,zircon U-Pb and Hf isotopic data of the Dongwanzi syenite,in order to put insights on its formation age and petrogenetic relationship with cumulates.展开更多
冀东晚古生代东湾子岩体由角闪石岩、少量辉石岩和辉长岩组成。典型的堆晶结构、全岩和镁铁质矿物(透辉石、角闪石)的上凸型稀土分布模式、相容元素含量低且变化范围大(如:角闪石岩中V=296×10^(-6)~673×10^(-6))的特征表明...冀东晚古生代东湾子岩体由角闪石岩、少量辉石岩和辉长岩组成。典型的堆晶结构、全岩和镁铁质矿物(透辉石、角闪石)的上凸型稀土分布模式、相容元素含量低且变化范围大(如:角闪石岩中V=296×10^(-6)~673×10^(-6))的特征表明了岩体的堆晶成因。计算得到的与辉石岩中的透辉石相平衡的熔体具有很高的稀土含量,轻重稀土分馏较为明显,富集大离子亲石元素(如:Sr,Ba,K),亏损高场强元素(如:Nb,Zr,Ti),具有典型的弧岩浆特征。透辉石和角闪石的矿物成分也具有弧岩浆的特征。高钙透辉石、大量的角闪石与黑云母的存在说明母岩浆富水。透辉石在高P_(H_2O)的状态下与熔体反应,生成角闪石的结构特征也证明了这一点。结合岩体的球化学特征,认为岩浆来源于富集的含有角闪石的尖晶石橄榄岩的部分熔融,母岩浆具有富水的特征(>3%)。考虑到岩体形成时代(~300Ma;Zhao et al.,2007)和地质背景,认为东湾子岩体与位于华北北缘的其它晚石炭-早二叠世的岩体形成于同一构造背景下,都是晚古生代时期古亚洲洋向华北板块之下俯冲的产物。展开更多
基金supported by the National Science Foundation of China(grants 41302042 and 41672217)the Fundamental Research Funds for the Central Universities(grants N170104022).
文摘Objective Though the Central Asian Orogenic Belt (CAOB) is characterized by widespread Phanerozoic crustal growth,there is little juvenile crust documented in its southeastern segment,northern margin of the North China Craton(NCC)(Zhang et al,2007,2009).Late Carboniferous Dongwanzi ultramafic-mafic cumulate complex occurs in northern margin of the NCC and is intruded by a syenite with depleted Sr-Nd isotopes (Ma et al.,2014).However,the age and petrogenesis of this syenite is poorly constrained.In this study,we present new petrological,zircon U-Pb and Hf isotopic data of the Dongwanzi syenite,in order to put insights on its formation age and petrogenetic relationship with cumulates.
文摘冀东晚古生代东湾子岩体由角闪石岩、少量辉石岩和辉长岩组成。典型的堆晶结构、全岩和镁铁质矿物(透辉石、角闪石)的上凸型稀土分布模式、相容元素含量低且变化范围大(如:角闪石岩中V=296×10^(-6)~673×10^(-6))的特征表明了岩体的堆晶成因。计算得到的与辉石岩中的透辉石相平衡的熔体具有很高的稀土含量,轻重稀土分馏较为明显,富集大离子亲石元素(如:Sr,Ba,K),亏损高场强元素(如:Nb,Zr,Ti),具有典型的弧岩浆特征。透辉石和角闪石的矿物成分也具有弧岩浆的特征。高钙透辉石、大量的角闪石与黑云母的存在说明母岩浆富水。透辉石在高P_(H_2O)的状态下与熔体反应,生成角闪石的结构特征也证明了这一点。结合岩体的球化学特征,认为岩浆来源于富集的含有角闪石的尖晶石橄榄岩的部分熔融,母岩浆具有富水的特征(>3%)。考虑到岩体形成时代(~300Ma;Zhao et al.,2007)和地质背景,认为东湾子岩体与位于华北北缘的其它晚石炭-早二叠世的岩体形成于同一构造背景下,都是晚古生代时期古亚洲洋向华北板块之下俯冲的产物。