扬子地块西北缘~2.09 Ga和~1.76 Ga花岗质岩石:Columbia超大陆聚合-裂解的岩浆记录  

Identification of the ~2.09 Ga and ~1.76 Ga Granitoids in the Northwestern Yangtze Block: Records of the Assembly and Break-Up of Columbia Supercontinent

作　　者：邓奇[1,2] 汪正江 任光明[1] 崔晓庄[1] 曹华文[1] 宁括步[1] 任飞 Deng Qi;Wang Zhengjiang;Ren Guangming;Cui Xiaozhuang;Cao Huawen;Ning Kuobu;Ren Fei(Chengdu Centery China Geological Survey,Chengdu 610081,China;Key Laboratory for Sedimentary Basin and Oil and Gas Resources,Ministry of Natural Resources,Chengdu 610081,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]自然资源部沉积盆地与油气资源重点实验室,四川成都610081

出　　处：《地球科学》2020年第9期3295-3312,共18页Earth Science

基　　金：国家自然科学基金项目(Nos.41772115,41872120);四川省科技计划项目(No.2019YJ0270);中国地质调查局项目(No.DD20190054);全国陆域及海区地质图件更新与共享(No.DD20190375)。

摘　　要：扬子地块保存了较多与Columbia超大陆演化有关的岩石记录,但是其聚合-裂解过程、在超大陆重建中的位置等还存在较大争论.对扬子地块西北缘碑坝地区马元花岗闪长岩和白玉钾长花岗岩进行了锆石U-Pb年代学、全岩地球化学和锆石Hf同位素研究.测年结果表明,上述花岗质岩石分别形成于~2 090 Ma和~1 760 Ma.地球化学组成上,马元~2 090 Ma花岗闪长岩受蚀变影响,表现出强过铝质的特点,微量元素低Sr、Cr、Ni,高Y和Yb,相对富集轻稀土、亏损高场强元素,与钙碱性花岗质岩石相似,锆石εHf(t)值为+0.91^+2.59;白玉~1 760 Ma钾长花岗岩高Si,富碱,低Al、Mg、Mn和P,A/CNK值在0.96~1.04之间,微量元素富集Th、Zr、Hf,相对富集Nb、Ta,贫Sr,稀土元素总量高,轻稀土富集,轻重稀土之间分异明显,并表现出强烈的负Eu异常,10 000×Ga/Al值为3.30~3.73,Zr+Nb+Ce+Y含量为797×10-6~1 495×10-6,锆石饱和温度高达897~939℃,表现出A型花岗岩的特点,锆石εHf(t)值为-13.58^-10.29.结合锆石微量元素、氧逸度及前人研究成果表明,马元2 090~2 080 Ma花岗质岩石最有可能形成于岩浆弧的环境,存在新生和古老地壳物质两种岩浆来源,而白玉1 790~1 760 Ma A型花岗岩形成于陆内裂谷盆地,来源于古老地壳物质的部分熔融,它们分别是Columbia超大陆聚合-裂解在扬子地块的地质响应.综合区域地球物理和岩浆-变质事件的成果,表明扬子地块可能位于Columbia超大陆的边部,与Laurentia克拉通相连.The Yangtze Block preserves large quantities of Paleoproterozoic rocks which hold the evidence of the Columbia supercontinent cycle, however, its evolution from the assembly to break-up and relative location in the palaeosupercontinent,are still in dispute. In this study, we present an integrated dataset of whole-rock geochemistry, zircon U-Pb age and Lu-Hf isotope of the Mayuan and Baiyu granitoids in the Beiba area of the northwestern Yangtze Block. Zircon U-Pb dating reveals that the Mayuan granodiorite and the Baiyu K-feldspar granite were emplaced at ~2 090 Ma and ~1 760 Ma, respectively. Geochemically, the Mayuan granodiorite shows strongly peraluminous characteristics with depletion in Sr, Cr, Ni, enrichment in Y and Yb, relatively enriched in LREE and depleted in HFSE, and these features bear resemblance to those of cal-alkali granite;in addition, its zircon Lu-Hf isotopic analyses yield positive εHf(t) values of +0.91 to +2.59. The Baiyu K-feldspar granite is alkali-rich and enriched in Sr, low Al, Mg, Mn and P, with A/CNK of 0.96-1.04;the trace elements show enrichment in Th, Na, Ta, Zr, Hf and depletion in Sr, Eu, with high total REE concentration, high LREE/HREE ratio, and strongly negative Eu anomalies;moreover,the granite has high HFSEs(Zr+Nb+Ce+Y=797×10-6-1 495×10-6) and 10 000×Ga/Al ratios(3.30-3.73). Together with high zircon saturation temperatures(897-939 ℃) from the K-feldspar granite, they are classified as A-type granites with negativeεHf(t) values from-13.58 to-10.29. Integrated with the analysis of trace elements and oxygen fugacity of zircon and previous research results, the Mayuan 2 090-2 080 Ma granitoids were likely to be generated by remelting of both juvenile and old crustal components within an arc-related setting;the Baiyu 1 790-1 760 Ma K-feldspar granite may be derived from partial melting of ancient crustal materials within the intracontinental rift setting. And they are likely to be the responses to the assembly and breakup of the Columbia supercontinent. Taking account

关 键 词：古元古代 锆石U-PB定年 地球化学 Columbia超大陆 构造演化 扬子地块西北缘 

分 类 号：P58[天文地球—岩石学]