华北板块北缘中段早中二叠世的构造属性:来自花岗岩类锆石U-Pb年代学及地球化学的制约  

Early-Middle Permian tectonic evolution of the central-northern margin of the North China Craton:Constraints from zircon U-Pb ages and geochemistry of the granitoids

作　　者：王挽琼[1] 徐仲元[1] 刘正宏[1] 赵庆英[1] 蒋孝君[1] 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2013年第9期2987-3003,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40972135;41272223);中国地质调查局项目(1212011120709)联合资助

摘　　要：内蒙古温都尔庙南-铁沙盖黑云角闪石英闪长岩和角闪黑云花岗闪长岩位于华北板块北缘中段晚古生代构造岩浆活动带中;锆石LA-ICP-MS U-Pb定年结果显示,其形成时代分别为271.8±2.4Ma,271.4±1.3Ma、268.7±1.3Ma。主量元素SiO2含量61.42%~71.73%,K2O含量3.10%~5.11%,K2O/Na2O值介于0.93~1.96之间,Mg#值介于42.54~49.93之间,A/CNK为0.90~1.03;副矿物为锆石、磷灰石和磁铁矿,属亚碱性高钾钙碱性系列、I型花岗岩类;富集轻稀土（LREEs）、大离子亲石元素（LILEs,Cs、Rb、K、Ba、Th和U）,亏损重稀土元素（HREEs）及高场强元素（HFSEs,Nb、Ta和Ti）,弱Eu负异常（δEu=0.55~0.95）,形成于活动大陆边缘弧环境,是上地壳部分熔融的产物。黑云角闪石英闪长岩和角闪黑云花岗闪长岩中发育大量暗色微粒包体（黑云闪长岩）,包体可能是岩石圈地幔部分熔融的产物,相对于寄主岩石贫Si、K富Fe、Mg、Ca、Ti、大离子亲石元素（LILEs,Rb、Cs、Sr和U）和高场强元素（HFSEs,Nb、Ta、Zr、Hf）。本文花岗岩类的侵位反映了早中二叠世古亚洲洋俯冲于华北板块北缘之下及岩浆混合作用的岩浆事件。This paper presents petrological, geochronological and geochemical study on Late Paleozoic intermediate-felsic intrusions from the Ondor Sam-Tieshagai area in Inner Mongolia, which is tectonically located in the central-northern margin of the North China Craton. These intrusions comprise mainly biotite-hornblende quartz diorite and hornblende-biotite granodiorite with abundant mafic enclaves in field. U-Pb dating of zircons from three samples by LA-ICP-MS yield weighed mean 2~6pb/23Su ages of 271.8 -＋ 2.4Ma, 271.4 -＋ 1.3Ma and 268.7 ＋ 1.3Ma, respectively. These rocks have SiO2 = 61.42% - 71.73% , KzO = 3. 10% - 5.11%, K20/ Na20 = 0. 93 ~ 1.96, Mg# = 42. 54 -49.93, A/CNK = 0. 90 - 1.03, features of high-K calc-alkaline I-type granitoids. They also show strong enrichments in light rare earth （LREEs） and large ion lithophile elements （LILEs, e. g. , Cs, Rb, Ba, K, Th and U） and depletions in high field-strength elements （HFSEs, e. g. , Nb, Ta and Ti） and heavy rare earth （HREEs）, with weakly negative Eu anomalies （3Eu = O. 55 ~ 0. 95）. The primary magma for granitoids could be mainly derived from partial melting of the upper crust. The mafic microgranular enclaves （MMEs） are biotite diorites, characterized by low Si and K, enrichment in Fe, Mg, Ca, Ti, LILEs （ Rb, Cs, Sr, U） and HFSEs （Nb, Ta, Zr, Hf） when compared with the host rocks, its primary magma could be mainly derived from partial melting of lithospheric mantle, implying an important role of magma mixing during the magmatic differentiation. The combined geochemical features of these intermediate-felsic intrusions and the MMEs likely indicate their formation in an active continental margin as a result of Middle Permian subduction of the Paleo-Asian Ocean beneath the northern margin of the North China Craton.

关 键 词：活动大陆边缘弧 I型花岗岩 暗色微粒包体 岩浆混合作用 晚古生代 内蒙古 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]