大别山鲁家寨花岗岩地球化学、锆石年代学和Hf同位素特征:扬子克拉通北东缘新元古代岩浆活动证据

Geochemistry,zircon geochronology and Hf isotopes of Lujiazhai granites from the Dabie Orogen: Evidence for the Neoproterozoic magmatism along the northeastern margin of Yangtze Block.

对大别山造山带的鲁家寨花岗岩进行了锆石U-Pb年代学、锆石Hf同位素和岩石地球化学研究。锆石LA-ICP-MS U-Pb定年结果表明鲁家寨花岗岩形成于新元古代（（816±17）Ma）。鲁家寨花岗岩总体具有高硅（Si O269.13%-75.47%）、准铝-弱过铝（A/CNK=0.98-1.01）的化学组成特征。稀土元素总量（∑REE）为（27.43-160.66）×10^-6,稀土元素配分曲线呈右倾型,具有弱的负Eu异常—正Eu异常。高场强元素（P、Nb、Ti等）强烈亏损,大离子亲石元素（K、Ba、Sr等）相对富集。锆石Hf同位素组成研究表明,鲁家寨新元古代花岗岩可能主要来源于与扬子陆核类似的大别山早前寒武纪变质基底的部分熔融,幔源岩浆不仅为古老地壳物质的部分熔融作用提供了热量,可能还直接参与了花岗岩的成岩作用。综合Rodinia超大陆古地理复原资料,推测扬子板块北东缘新元古代早期为接受大洋俯冲的活动大陆边缘,而形成于816 Ma的鲁家寨岩体具有后碰撞岩浆活动的特征,是弧陆碰撞造山带构造（重力/拉张）垮塌产物。

The Lujiazhai granitic pluton located in the southern Dabie Orogen was studied by zircon LA-ICP-MS U-Pb dating,zircon Hf isotope and bulk geochemistry analyses.LA-ICP-MS zircon U-Pb dating gave the age of 816±17 Ma for the Lujiazhai granites,revealing that the pluton was emplaced in the Neoproterozoic.All bulk samples are high in SiO2（69.13%—75.47%）,with moderate A/CNK values（0.98—1.01,averaged at 1.0）,inferring an I-type granite affinity.The concentration of total rare earth elements（REEs） varies in the range of 27.43×10-6 to 160.66×10-6.The Lujiazhai granites are characterized by an enriched LREE pattern with slightly negative to positive Eu anomalies.They are enriched in large ion lithophile elements（e.g.K,Ba,Sr）,but depleted in high field strength elements（e.g.P,Nb,Ti）.Zircon Hf isotopic data indicate that the Lujiazhai Neoproterozoic granitic pluton in the southern Dabie Orogen was likely formed by magmas derived from partial melting of Early Precambrian metamorphic complex,accompanied by the heating and possible assimilation of mantle-derived magmas.By combining studies of the paleogeographic reconstruction of the Rodinia supercontinent,we propose that since the early Neoproterozoic,the northeastern margin of the Yangtze block might have been under an active continental margin setting induced by subduction of an oceanic plate.In this tectonic regime,the Lujiazhai granites were derived by partial melting of ancient crustal materials induced by the underplating or intracrustal heating of hot mantle-derived magmas.After the cease of subduction and consequent continent-arc collision,this area was then likely dominated by post-collisional extension or rifting tectonically,related to the break-up of the Rodinia supercontinent.