南秦岭地块紫阳地区早古生代岩石圈伸展规律、动力学机制及基性岩墙成因  

Early Paleozoic lithospheric extension law, dynamic mechanism, origin of mafic dykes in Ziyang, South Qinling Block, China

作　　者：刘燊[1] 冯彩霞[1] 陈晓青 赵慧博 徐静妍 范焱 LIU Shen;FENG CaiXia;CHEN XiaoQing;ZHAO HuiBo;XU JingYan;FAN Yan(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi an 710069,China;College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [2]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2023年第3期938-962,共25页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41573022);陕西省自然科学基础研究计划重点项目(2023-JC-ZD-16)联合资助。

摘　　要：南秦岭地块紫阳地区广泛出露早古生代基性岩墙群,其研究具有重要的地球动力学意义。虽然如此,已有相关研究目前主要集中于志留纪基性岩墙群方面,而对早古生代(如,寒武纪、奥陶纪)基性岩墙群的研究仍相对薄弱。从而制约了对南秦岭早古生代岩石圈伸展过程相关问题(如,时空分布规律、地幔性质、动力学机制和相关成矿作用)的总体把握。鉴于尚存的科学问题,本研究选取康家坪、梨树梁、大竹坪、清明寨、苟家山、庙梁上、曾家山和毛坝村的基性岩墙群为研究对象,开展了矿物学、岩石学、锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素方面的研究,对其精细时代格局、成因及成岩动力学背景进行了系统探讨。研究结果显示,紫阳早古生代基性岩墙以辉绿岩和辉绿玢岩为主,形成时代为奥陶纪(478.8-486Ma),属碱性系列岩石(K_(2)O+Na_(2)O变化范围为4.10%-5.14%)。另外,基性岩墙群具有富集LREE、Rb、Ba、Sr、Nb、Ta、Zr、Hf和Eu(Eu/Eu*=1.13-1.35),亏损HREE、U、Pb和Ti的典型地球化学特征。(87Sr/86Sr)i=0.7044-0.7050、εNd(t)=3.1-3.6、εHf(t)=4.4-12.1,176Hf/177Hf=0.282634-0.282846,暗示基性岩墙为地幔柱作用过程亏损岩石圈或软流圈地幔部分熔融作用的产物。另外,在辉绿岩成岩过程经历了橄榄石和单斜辉石的分离结晶,但地壳混染的影响不明显。Early Paleozoic mafic dyke swarms are widely exposed in Ziyang area, South Qinling Block, and its research has important geodynamic significance. Nevertheless, the existing research-related is mainly focused on the Silurian mafic dyke swarms, while the research on the Early Paleozoic(such as Cambrian and Ordovician) mafic dyke swarms is still relatively weak. Thus, it restricts the overall grasp of the problems related to the Early Paleozoic lithospheric extension process in the South Qinling Block, such as the temporal and spatial distribution law, mantle properties, dynamic mechanism and related mineralization. In view of the remaining scientific problems, this study selects the mafic dyke swarms in Kangjiaping, Lishuliang, Dazhuping, Qingmingzhai, Goujiashan, Miaoliangshang, Zengjiashan and Maoba Village as the research objects, and carries out the research on mineralogy, petrology, zircon U-Pb chronology, geochemistry and Sr, Nd and Hf isotope, and the age pattern, origin and genetic dynamic background are systematically discussed. The results show that the Early Paleozoic mafic dykes are mainly dolerite and sillite, which are formed in the Ordovician(478.8-486 Ma) and belong to alkaline series rocks(K_(2)O+Na_(2)O variation range is 4.10% and 5.14%). In addition, the mafic dykes in the study area is characterized by the geochemical characteristics of enrichment of LREE, Rb, Ba, Sr, Nb, Ta, Zr, HF and Eu(Eu/Eu*=1.13-1.35), typical characteristics of depleted HREE, U, Pb and Ti,(87Sr/86Sr)i=0.7044-0.7050, εNd(t)=3.1-3.6, εHf(t)=4.4-12,1176Hf/177Hf=0.282634-0.282846, suggesting that the dykes studied is the product of partial melting of the depleted lithospheric mantle or asthenosphere mantle in the process of mantle plume. In addition, olivine and clinopyroxene were separated and crystallized in the genetic process of the dykes, but the influence of crustal contamination is not obvious.

关 键 词：早古生代 基性岩墙群 成因 成岩动力学 南秦岭地块 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]