The Petrological and Geochemical Evolution of Ediacaran Rare-Metal Bearing A-type Granites from the Jabal Aja Complex, Northern Arabian Shield, Saudi Arabia  

作　　者：Shehta E.ABDALLAH Mokhles K.AZER Abdullah S.AL SHAMMARI 

机构地区：[1]Geology Department,Faculty of Science,Zagazig University,44519,Zagazig,Egypt [2]Geological Sciences Department,National Research Centre,12622 Dokki,Cairo,Egypt [3]Faculty of Science,Ha’il University,2440 Ha’il,Saudi Arabia

出　　处：《Acta Geologica Sinica(English Edition)》2020年第3期743-762,共20页地质学报（英文版）

基　　金：The authors extend their appreciation to the Deanship of Scientific Research;Ha’il University;for supporting this work through research project no.SCB-0150175

摘　　要：New fieldwork, mineralogical and geochemical data and interpretations are presented for the rare-metal bearing A-type granites of the Aja intrusive complex(AIC) in the northern segment of the Arabian Shield. This complex is characterized by discontinuous ring-shaped outcrops cut by later faulting. The A-type rocks of the AIC are late Neoproterozoic post-collisional granites, including alkali feldspar granite, alkaline granite and peralkaline granite. They represent the outer zones of the AIC, surrounding a core of older rocks including monzogranite, syenogranite and granophyre granite. The sharp contacts between A-type granites of the outer zone and the different granitic rocks of the inner zone suggest that the AIC was emplaced as different phases over a time interval, following complete crystallization of earlier batches. The A-type granites represent the late intrusive phases of the AIC, which were emplaced during tectonic extension, as shown by the emplacement of dykes synchronous with the granite emplacement and the presence of cataclastic features. The A-type granites consist of K-feldspars, quartz, albite, amphiboles and sodic pyroxene with a wide variety of accessory minerals, including Fe-Ti oxides, zircon, allanite, fluorite, monazite, titanite, apatite, columbite, xenotime and epidote. They are highly evolved(71.3–75.8 wt% SiO2) and display the typical geochemical characteristics of post-collisional, within-plate granites. They are rare-metal granites enriched in total alkalis, Nb, Zr, Y, Ga, Ta, REE with low CaO, MgO, Ba, and Sr. Eu-negative anomalies(Eu/Eu* = 0.17–0.37) of the A-type granites reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interactions. The chemical characteristics indicate that the A-type granites of the AIC represent products of extreme fractional crystallization involving alkali feldspar, quartz and, to a lesser extent, ferromagnesian minerals. The parent magma was derived from the partial melting of a juvenile crustal protolith with a mantle

关 键 词：ring complex rare-metal bearing granites sodic amphibole sodic pyroxene within-plate Arabian Shield 

分 类 号：P588.121[天文地球—岩石学] P59[天文地球—地质学]