赣中变质岩带地质地球化学演化特征  

Geological and Geochemical Evolution Characteristics of the Metamorphic Belt in Central Jiangxi

作　　者：胡恭任[1] 刘丛强[2] 于瑞莲[1] 

机构地区：[1]华侨大学环境科学与工程系 [2]中国科学院地球化学研究所,贵阳550002

出　　处：《地球学报》2006年第1期35-42,共8页Acta Geoscientica Sinica

基　　金：福建省自然科学基金(编号:D0310017);南京大学内生金属矿床成矿机制研究国家重点实验室开放基金;华侨大学自然科研资金(编号:02HZR01)联合资助成果。

摘　　要：赣中变质岩带由结晶基底和褶皱基底组成。从结晶基底→褶皱基底,变质泥质岩类SI O2含量降低,AL2O3含量增加;变粒岩、石英片岩、硅质岩SI O2含量显著升高,AL2O3含量显著降低;NA2O含量显著降低,K2O的含量有明显的升高,NA2O/K2O值呈显著的降低趋势;FEO、MGO、TI O2及全铁含量(FE2O3+FEO)呈降低的趋势,但FE2O3升高,FE2O3/FEO值显著增高。铁族元素TI、V、CR升高,MN、CO、NI降低;亲铜元素ZN显著升高;大离子亲石元素LI、RB、SR显著降低,U、TH、BA显著升高,SR/BA值急剧降低;LA、CE、YB、NB、Y元素升高;稀土总量、轻稀土含量、轻重稀土比值、轻重稀土相互分离程度、EU亏损程度增加,说明它们原岩沉积环境的差异性,但它们的重稀土含量、LA/CE值、SM/ND值变化很小,稀土配分曲线相互平行反映它们源区岩石的一致性及继承性。从结晶基底→褶皱基底,岩石的ΕND(0)、(^(206)PB/^(204)PB)I、(^(207)PB/^(204)PB)I、(^(208)PB/^(204)PB)I值由低→高;地壳趋于成熟,结晶基底形成于岛弧环境,褶皱基底形成于活动大陆边缘环境。Isotope chronologic, geological and geochemical studies show that there exists a Middle Proterozoic crystalline basement in the deformation metamorphic belt of central Jiangxi and that after Middle Proterozoic the crystalline basement at least underwent 2 tectono-thermal events (Jinning and Caledonian). Petrochemical and REE studies demonstrate that the crystalline basement is mainly composed of parametamorphic rocks occasionally interlayered with orthometamorphic rocks. Folded basement rocks show increasing metamorphism at the center of the migmatite. There is a regular variation in petrochemical and REE composition from the crystalline basement to folded basement rocks, i.e. an increase of SiO_2 and K_2O+Na_2O and a decrease of TFeO+MgO+CaO+TiO_2, an increase of REE, LREE and LREE/HREE and a conversion from the slightly negative Eu anomaly to the strong one. An isotope geochemical study reveals a regular variation from the crystalline basement to folded-basement rocks, i.e., the values of ε_ Nd (0), ( ~ 206 Pb/ ~ 204 Pb)_i, ( ~ 207 Pb/ ~ 204 Pb)_i and ( ~ 208 Pb/ ~ 204 Pb)_i increase. The above characteristics also exhibit the tectonic evolution in central Jiangxi from island arc to active continental margins in the period from Middle Proterozoic to Sinian and Cambrian.

关 键 词：赣中变质岩带 元素地球化学 同位素地球化学 结晶基底 褶皱基底 

分 类 号：P5[天文地球—地质学]