江南东段华夏与扬子陆块碰撞时间的研究  

A Study of the Collision Timing of Yangtze and Cathaysia Blocks in the Eastern Jiangnan Orogenic Belt,South China

作　　者：陈小勇[1] 陈国华[1,2] 舒立旻[2] 姚金龙[1] 舒良树[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,江苏南京210093 [2]江西省地矿局九一二大队,江西鹰潭335000

出　　处：《新疆地质》2015年第4期520-528,共9页Xinjiang Geology

基　　金：国家基础研究计划(2012CB416701);国家自然科学基金委(41330208、41272226);中国地质科学院地质所(201211093-1)共同资助

摘　　要：江南造山带是扬子陆块和华夏陆块在新元古代的碰撞造山带,碰撞时间存在争议。通过对东段怀玉地体前南华纪岩层和南华纪盖层的沉积序列、岩石组合、碎屑锆石年代学和Hf同位素组分的研究,初步确定其碰撞时间。研究表明,怀玉地体南西侧具岛弧亲缘性,碎屑锆石测年值集中于800-900 Ma;北东缘具弧前盆地性质,碎屑锆石测年值为800-940 Ma。南华纪盖层的碎屑锆石记录了多期构造-岩浆活动信息：750-890 Ma、1 670-2 070 Ma和2 385-2 550 Ma。Hf同位素数据揭示,前南华系碎屑锆石大多呈正的εHf（t）值和中元古代晚期模式年龄,南华纪盖层碎屑锆石大多呈负的εHf（t）值,碎屑物多源自早先的火山岛弧。年代学和和Hf同位素数据揭示,扬子陆块和华夏陆块在800 Ma完成碰撞。The Jiangnan orogen is a collision zone between the Yangtze and Cathaysia Blocks, and its collision timing was long-time debated.This paper presents results from zircon U-Pb geochronology and Lu-Hf isotopes from detrital zircons of pre-Nanhua clastic rocks and late Neoproterozoic（Nanhua） cover in the Huaiyu terrane of the eastern Jiangnan orogen. The sedimentary sequences in southwestern Huaiyu are composed of marine volcaniclastic turbidite and tuffaceous phyllite,exhibiting an arc affinity;U-Pb dating data from detrital zircons yield a single age population of 800~900Ma.Whereas those in the northeastern Huaiyu consist of pebbly feldspathic sandstones and greywacke interbedded with intermediate-basic volcanic rocks, suggesting an affinity of fore-arc basin;the dating data concentrate in the range 800~940 Ma. However,the Nanhua cover sequence preserves zircons from multiple sources with age populations of 750~890Ma,1 670~2 070 Ma and 2 385-2 550 Ma.Moreover,Hf isotopic compositions reveal that most detrital zircons from the northern and southern Huaiyu yielded positive εHf（t） values and late Mesoproterozoic model ages,while those of the Nanhua cover sequence show negative εHf（t） values.The Hf isotopic data therefore suggest that the northern and southern Huaiyu sequences were soured from a Neoproterozoic arc;the geochronological and Hf isotopic data witness that an assembly of the Yangtze and Cathaysia Blocks was finished at ca. 800 Ma.

关 键 词：新元古代 碎屑锆石 扬子 华夏 江南造山带 

分 类 号：P597.3[天文地球—地球化学] P542[天文地球—地质学]