华北克拉通南缘潘河～1.5Ga正长岩的厘定及其构造意义  

Geochronology and geochemistry of the Mesoproterozoic Panhe syenites in the southern margin of North China Craton and its tectonic implications

作　　者：曾令君[1,2] 包志伟[1] 赵太平[1] 姚军明[1] 周栋[1,2] 

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广州510640 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2013年第7期2425-2436,共12页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划(2012CB416602);河南省卢氏县北方矿业公司委托项目联合资助

摘　　要：华北克拉通是否曾是Columbia超大陆的组成部分并具有一致的裂解过程一直存在争议,而已知的中元古代非造山岩浆组合集中分布于华北克拉通北缘是引起有关裂解过程争论的重要原因。作者近来在华北克拉通南缘,河南省卢氏县潘河地区,厘定了一组中元古代走向近东西的正长岩脉群。正长岩LA-ICP-MS锆石U-Pb年龄为1469±8Ma(MSWD=1.4)。岩石类型主要为黑云母正长岩,局部有少量霞石正长岩。岩体的SiO2变化于51.3%～65.7%之间,碱含量较高,K2O+Na2O总量8.32%～13.0%,铝含量较高(Al2O3=18.7%～20.0%),为碱性过铝质岩类。岩体轻重稀土分馏较为显著(La/Yb)N=14.5～34.5,具有显著的Eu负异常(δEu=0.2～0.3),强烈富集Rb、Ba、Th等大离子亲石元素和Nb、Ta、Nd、Tb等高场强元素,而Sr、Ti、P、Eu等元素显著亏损。岩石εHf(t)=-14.79～+8.16,Hf模式年龄为2.93～1.74Ga,指示成岩物质主要来源于富集岩石圈地幔的部分熔融并有地壳物质的加入。岩体形成于板内伸展构造环境,这表明华北克拉通的南缘也同时记录了华北克拉通曾经在中元古代发生过大规模的伸展作用,其伸展过程可能与Columbia超大陆的裂解有关。It has long been an issue of debate whether the North China Craton was assembled into the Columbia or Nuna supercontinent and experienced breakup processes congruent with the other cratons. Controversy regarding the breakup processes of the North China Craton is partly due to the known Mesoproterozoic anorogenic magmatisms are mainly distributed in the northern margin of North China Craton. Series of Mesoproterozoic syenite veins of nearly EW-striking were discovered recently in the southern margin of North China Craton at the Panhe area in Lushi County,Henan Province. The syenites are composed of silica-saturated biotite syenite and silica-undersaturated nepheline syenite,within which the later only occurs locally. LA-ICP-MS zircon U-Pb dating of the biotite syenite yields a concordia age of 1469 ± 8Ma （ MSWD = 1. 4） . The Panhe syenites are per-alkaline and peraluminous with SiO 2 and Al 2 O 3 contents vary in ranges of 51. 3% ～ 65. 7% and 18. 7% ～ 20. 0% ,respectively. The syenites exhibit steep right declining REE patterns （ La / Yb） N = 14. 5 ～ 34. 5） with significant negative Eu anomalies （ δEu = 0. 2 ～ 0. 3） ,enriched in LILE （ Rb,Ba,Th,etc. ） and HFSE （ Nb,Ta,Nd,Tb） ,and considerably depleted in Sr,Ti,and P. The ε Hf （ t） values range from -14. 79 to ＋8. 16 and Hf model ages vary in range of 2. 93Ga to 1. 74Ga,which suggest that the syenites might have been derived from partial melting of the lithospheric mantle that was fertilized by delaminating of thickened crust,and underwent assimilation of silica-rich crustal material and fractional crystallization （ AFC） processes. The syenites were formed under extension tectonic regime. It means that the southern margin of North China Craton records the extension process of the NCC at Mesoproterozoic. And the process might be related to the breakup of the Columbia supercontinent.

关 键 词：华北克拉通南缘 正长岩 Columbia超大陆 裂解 中元古代 

分 类 号：P588.122[天文地球—岩石学]