江西崇义铁木里钨铁矿区内辉绿玢岩的年代学、地球化学特征及地质意义

华南地区中生代基性岩浆岩以拉斑玄武岩系列为主,碱性系列少见.江西崇义铁木里地区发育由碱性辉绿玢岩和A型花岗岩组成的双峰式侵入岩组合,对其中的辉绿玢岩开展了矿物学、年代学和地球化学研究.辉绿玢岩的斑晶矿物以次透辉石为主,少量为透辉石和普通辉石;基质中的斜长石为中长石(Ab=39.11%～43.30%),角闪石为钛闪石.LA-ICP-MS锆石U-Pb定年结果表明辉绿玢岩的形成不早于136.6 Ma.岩石具有低SiO₂(41.73%～46.68%)、TiO₂(1.72%～1.94%),富TFeO(7.64%～9.24%)、Al₂O₃(15.70%～17.22%),全碱含量高(5.28%～6.60%)的特征,Mg^#值为0.51～0.54,属于碱性玄武岩系列.轻重稀土元素之间、轻稀土元素内部分馏强((La/Yb)_N=17.58～22.28,(La/Sm)_N=4.72～5.18),Eu异常不明显(δEu=0.84～0.99),显著富集大离子亲石元...

Geochronology,Geochemistry and Geological Implications of Diabase Porphyrite in Tiemuli W-Fe Deposit,Chongyi County,Jiangxi Province

The Mesozoic basic igneous rock in South China is dominated by tholeiite series,while the alkali series is rare.Bimodal intrusive pluton composed of alkali diabase porphyrite and A-type granite occurs in Tiemuli area,Chongyi County,Jiangxi Province.Mineralogical,geochronological and geochemical analyses of the diabase porphyrite were carried out.The Tiemuli diabase porphyrite displays porphyritic texture.Phenocrysts are dominated by salite,with minor diopside and augite,while groundmass minerals comprise andesite (with Ab values of 39.11%-43.30%),kaersutite and clinopyroxene chemically equivalent to phenocrysts.The diabase porphyrite was emplaced after the granite (136.6 Ma) and belongs to alkali basalt series,characterized by low SiO2(41.73%-46.68%) and TiO2(1.72%-1.94%) contents,high TFeO (7.64%-9.24%),Al2O3(15.70%-17.22%)and alkali (5.28%-6.60%) contents,and moderate Mg#values (molar ratios of MgO/(MgO+TFeO),0.51-0.54).The fractionation between light rare earth elements (LREEs) and high rare earth elements (HREEs) and fractionation of LREEs are remarkable ((La/Yb)N=17.58-22.28,(La/Sm)N=4.72-5.18),while the Eu anormalies are negligible (δEu=0.84-0.99).All rocks are significantly enriched in large iron lithophile elements (LILEs) and are slightly enriched in high field strength elements(HFSEs),with lower contents of transition elements than primitive mantle.They haveεNd,(87Sr/86Sr)i,(206Pb/204Pb)i,(207Pb/204Pb)i and (208Pb/204Pb)ivalues of+3.45,0.707 5,18.769 9,15.733 7 and 39.110 0,respectively,displaying transitional features between OIB and EMII.Mineralogical,geochemical and Nd-Hf isotopic characteristics suggest that the Tiemuli diabase porphyrite was generated in asthenosphere and the partial melting took place in garnet stability field.The alkali basalt magma was derived from small degree of decompression melting of depleted asthenospheric mantle and contamination of crustal materials was minor.Fractional crystallization of clinopyroxene,apatite and Fe-Ti oxides took place during the basaltic magma evolution.Some enriched components from lithospheric mantle might be involved in.The Cretaceous alkali basaltic rocks developed interior of South China were formed in intracontinental extension (rift-like) regime related to regional lithospheric extension and deeppenetrating faults.