Petrology and geochemistry at the Lower zone-Middle zone transition of the Panzhihua intrusion,SW China:Implications for differentiation and oxide ore genesis

作     者：Kwan-Nang Pang Mei-Fu Zhou Liang Qi Sun-Lin Chung Chiu-Hong Chu Hao-Yang Lee 

作者机构：Department of GeosciencesNational Taiwan University Department of Earth SciencesThe University of Hong Kong Institute of GeochemistryChinese Academy of Sciences 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2013年第4卷第5期

页      面：517-533页

核心收录：

学科分类：081803[工学-地质工程] 08[工学] 0708[理学-地球物理学] 0818[工学-地质资源与地质工程] 0704[理学-天文学] 

基　　金：supported by the Research Grant Council of Hong Kong(HKU707012P)to MFZ a post-doctoral fellowship awarded by the National Science Council(NSC), Taiwan to KNP 

主　　题：Fe-Ti oxides Layered intrusion Microgabbro Panzhihua Emeishan 

摘      要：A sequence of gabbros showing isotropic,layered and fine-grained textures is exposed in the Nalaqing mine at the southern tip of the～260 Ma Panzhihua intrusion,SW *** field relations,structure,texture and mineralogy of the rocks indicate that the sequence represents the transition between the Lower zone and Middle zone of the *** gabbros characteristic of the Lower zone pass upward to layered gabbros of the Middle zone through a～5 m-thick microgabbro sheet,within and close to which small-scaled, concordant Fe-Ti oxide ore horizons are *** fractionation between HFSE and REE in a subset of samples is ascribed to cumulus titanomagnetite into which HFSE are preferentially incorporated over REE,as reflected in the parallel relations between Nb/La,Hf/Sm and Ti/Ti＊.Both the isotropic and layered gabbros display cumulate textures and have similar mineral compositions（Mg# of clinopyroxene =～76-79 and An59-61）,isotopic compositions[（87Sr/86Sr）i = 0.7044-0.7045 andεNd（t） = ＋2.4 to ＋3.9]and trapped liquid contents inferred from Zr abundance（～17-34 ppm）.However,there are substantial variations in elemental abundances（V,Cr and PGE） and ratios（Ti/V,La/Yb,Ba/Y and Cu/Pd） between the two types of gabbros,features that cannot be explained by cumulate formation from a common magma in a closed *** microgabbros generally resemble high-Ti Emeishan basalts in major element compositions,but their low trace element abundances indicate some lost of residual liquid is inevitable despite rapid nucleation and *** with available data and observations,we propose a model involving in-situ crystallization,followed by magma recharge and closed-system fractionation to explain the formation of texturally distinctive gabbros at Nalaqing and the evolution of the lower part of the Panzhihua intrusion.