Age, geochemistry and origin of peraluminous A-Type granitoids of the Ablah-Shuwas pluton, Ablah graben, Arabian shield | Szegedi Tudományegyetem, Ásványtani, Geokémiai és Kőzettani Tanszék

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Age, geochemistry and origin of peraluminous A-Type granitoids of the Ablah-Shuwas pluton, Ablah graben, Arabian shield

Acta Mineralogica-Petrographica, Szeged 2001, Vol. 42, pp. 5-20

Article informations

Mohammed Rashad H.Moufti

The A-type granitoids of the Ablah-Shuwas pluton, situated in the Ablah graben of the Asir terrane, occur as discontinuous ring complexes, cone sheets and irregular bodies. They intrude into the younger diorite and tonalite rocks of probably 744±22 Ma old. Their emplacement is contemporaneous with the movement (~610 Ma or later) along the Umm Farwah shear zone, which cuts the eastern margin of the rift-related epiclastic and volcanic complex of the Ablah group. The whole rock Rb-Sr isochrons indicate shear zone compatible ages of 617±17 and 605±5 Ma for the syenites and quartz syenites-granites, respectively. The low initial 87Sr/86Sr ratios (0.7035-0.7038) in the A-type granitoids indicate either a mantle origin or a Rbdepleted crustal source. The granitoids show the petrological and geochemical characteristics of a typical A-type granite. They are composed of suites of cogenetic syenites, quartz syenites, and syenogranites with iron- and alkali-rich silicates, high FeOt/MgO and Ga/Al ratios. They show the marked enrichment of high field strength elements (Zr, Nb, Y and Ga), Zn, and Na2O+K2O and depletion in CaO and MgO with a large negative Ba anomaly. The origin of A-type granitoids is related with the Umm Farwah shear zone that trigger off partial melting in the volatiles and LIL-enriched metasomatized mantle. The rise of this mantle flux through reactivated; deep-seated; heat-laden shearzones/faults caused crustal fusion in the arc-related lower mafic and upper volcano-plutonic crust of intermediate to felsic compositions to produce A-type granitoids.



A-type granitoids, Ablah-graben, Ablah-Shuwas pluton, acta2001, Asir terrane, crustal fusion, metasomatized mantle, quartz syenites, ring complexes, syenites, syenogranites, Umm Farwah shear zone




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