Paleoproterozoic Granitoids on Liaodong Peninsula, North China Craton

Paleoproterozoic granitoids are an important constituent of the Jiao-Liao-Ji Belt(JLJB). The spatial-temporal distribution and types of Paleoproterozoic granitoids are closely related to the evolution of the JLJB. In this paper, we review the field occurrence, petrography, geochronology, and geochemistry of Paleoproterozoic granitoids on Liaodong Peninsula, northeast China. The Paleoproterozoic granitoids can be divided into pre-tectonic(~2.15 Ga;peak age=2.18 Ga) and post-tectonic(~1.85 Ga) granitoids. The pre-tectonic granitoids are magnetite and hornblende-biotite monzogranites and granodiorites. Pre-tectonic monzogranites are widespread in the JLJB and have A2-type affinities. In contrast, pretectonic granodiorites are only present in the Simenzi area and have adakitic affinities. The post-tectonic granitoids consist of porphyritic monzogranite, syenite, diorite, granodiorite, quartz monzonite, monzogranite, and granitic pegmatite, which are adakitic rocks and I-, S-, and A2-type granitoids. The assemblage of pre-tectonic A2-type granitoids and adakitic rocks indicates the initial tectonic setting of the JLJB was a continental back-arc basin. The assemblage of post-tectonic adakitic rocks and I-, S-, and A2-type granitoids indicates a post-collisional setting. The 2.20-2.15 Ga A2-type granitoids and adakitic rocks were associated with the initial stage of back-arc extension, and the peak of back-arc extension is inferred from the subsequent(2.15-2.10 Ga) mafic intrusive activity. The ~1.90 Ga adakitic rocks mark the beginning of the postcollisional stage, which was followed by the intrusion of low-temperature S-and I-type granitoids. High-to low-pressure granitoids(S-type) were generated during the peak of post-collisional lithospheric delamination and asthenospheric upwelling. The emplacement of later granitic pegmatites occurred during the waning of the orogeny.

A Comparison between the ~1.08–1.13 Ga Volcano-Sedimentary Koras Group and Plutonic Keimoes Suite: Insights into the Post-Collisional Tectono-Magmatic Evolution of the Eastern Namaqua Metamorphic Province, South Africa

Along the eastern margin of the Mesoproterozoic Namaqua metamorphic province(NMP) of southern Africa are a bimodal volcano-sedimentary succession, the ~1.13–1.10 Ga Koras Group, composed of rhyolitic porphyries and basaltic andesites, and the ~1.11–1.07 Ga late-to post-tectonic granitoids of the Keimoes Suite. This review examines existing whole-rock major-and trace-element data, along with isotope chemistry(with some new isotopic data), to investigate the role these two magmatic successions played in terms of post-collisional magmatism of the eastern NMP near the boundary with the Archean Kaapvaal Craton. The Keimoes Suite comprises variably porphyritic biotite monzogranites and granodiorites, with a charnockitic member. They are metaluminous to weakly peraluminous, ferroan, and calc-alkalic. They exhibit large ion lithophile(LIL) element enrichment relative to the high field strength elements(HFSE) with depletions in Ba, Sr, Nb, P, Eu and Ti, and enrichments in Th, U and Pb. Isotopic values(ε_(Nd)(t): 2.78 to-2.95,but down to-8.58 for one granite, depleted mantle Nd model ages(T_(DM)): 1.62–1.99 Ga, but up to 2.55 Ga;initial ^(87)Sr/^(86)Sr: 0.652 82–0.771 30) suggest derivation from weakly to mildly enriched(and radiogenic)sources of Meso-to Paleoproterozoic age, the former of more juvenile character. The Koras Group is characterized by a bimodal succession of calcic to calc-alkalic, magnesian and tholeiitic basaltic andesites and mostly metaluminous to peralkaline rhyolitic porphyries. Two successions are recognised, an older, lower succession that extruded at ~1.13 Ga, and a younger, upper succession at ~1.10 Ga. The rhyolitic porphyries of both successions show similar LILE/HFSE enrichment and the same element enrichments and depletions as the Keimoes Suite granitoids. The upper succession is consistently more fractionated in terms of both whole-rock major and trace element chemistry, and, isotopically, has a greater enriched source component(ε_(Nd(t):-0.69 to-4.26;T_(DM): 1.64–2.44 Ga), relative to the lower succession(ε_(Nd(t): 0.74–5.62;T_(DM): 1.28–2.12 Ga). Crystal fractionation of plagioclase and K-feldspar appears to have played a role in bringing about compositional variation in many of the granites. These were derived from partial melting of mainly igneous with subordinate sedimentary sources from mostly lower crustal depths, although some granitoids have indications of a possible mantle source component. The lower succession of the Koras Group was derived by partial melting of subduction-influenced enriched mantle giving rise to mafic magmas that fractionated to give rise to the rhyolitic porphyries. The upper succession rhyolites were derived by crustal melting due to the input of mafic magmatism. Crystal fractionation was the main compositional driver for both successions. The Keimoes Suite granitoids and the Koras Group are associated with extensional regimes subsequent to the main deformational episode in the eastern NMP.