Petrogenesis and Tectonic Implications of the Jabal Hadb Ad Dayheen Granitic Complex, Central Arabian Shield.

The Jabal Hadb Ad Dayheen granitic complex in central Saudi Arabia is an alkaline granitic ring complex associated with a collapsed caldera. It mainly consists of monzogranite in the center, biotite-hornblende porphyritic granite, and biotite-aegirine-riebeckite granite, intruded by some felsic and mafic dikes. The petrological and geochemical characteristics show that the granitic suites consist of metalminous-peralkaline A-type granites. The secondary ion mass spectrometry (SIMS) zircon U-Pb analysis yielded 206Pb/238U ages of 613.3 ± 8.1–603.8 ± 3.8, 602.4 ± 3.8, 596 ± 5.6 Ma for biotitehornblende porphyritic granite, microgranite, and biotite-aegirine-riebeckite granite, respectively. The trace element characteristics and positive εHf(t) values (3.2–12.2) indicate that the granitic rocks of the Dayheen Ring Complex are mainly derived from the juvenile crust with the involvement of mantle-derived materials. Combined with the regional tectonic evolution, the formation of the Dayheen Ring Complex mainly covered four periods: (1) subduction initiation and formation of arc terranes (870–620 Ma)—volcanic craters formed during this period provided the channel for alkaline complex intrusion; (2) collision between East and West Gondwana continents and formation of the north East African Orogen (640−613 Ma)—monzogranite stock at the center of the ring complex emplaced during this period; (3) post-collision extension and collapse (613−602 Ma)—red metaluminous biotite-hornblende porphyritic granite and microgranite sheets in the rim of the Dayheen Ring Complex emplaced during this period; (4) within-plate extension (602 − 545 Ma)—white peralkaline biotite-aegirine-riebeckite granite and plenty of felsic and mafic dikes in the rim mainly formed during this period. The granitic rocks of the Dayheen Ring Complex mainly formed during the transitional stage of post-collison to within-plate extension after the collision between East and West Gondwana continents, and part of them formed during the early stage of the within-plate extension. U, Th, Zr, Nb, and rare earth element mineralization mainly formed during the early stage of the last period, having a close relationship with the intrusion of white peralkaline biotite-aegirine-riebeckite granite. [ABSTRACT FROM AUTHOR]