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The Aqishan-Yamansu belt in the Eastern Tianshan (Xinjiang, NW China) is an important mineralization belt. The belt mainly comprises Carboniferous volcanic, volcaniclastic and clastic rocks, and hosts many intermediate–felsic intrusions and Fe (–Cu) deposits. The biotite diorite, felsic brecciated tuff, granodiorite and syenite from the western Aqishan-Yamansu belt are newly zircon U–Pb dated to be 316.7 ± 1.4 Ma, 315.6 ± 2.6 Ma, 305.8 ± 1.9 Ma and 252.5 ± 1.4 Ma, respectively. The mafic rocks (mafic brecciated tuff and diabase porphyry) are tholeiitic to calc-alkaline series, LILE-rich (e.g., Rb, Ba and Pb), HFSE-depleted (e.g., Nb and Ta), and have high Mg # (44–60), Nb/Ta (15.0–20.0), Ba/La (>30) and Ba/Nb (>57) values/ratios, and low Th/Yb ratios (<1), probably originating from mantle wedge metasomatized by slab-derived fluids. The intermediate–felsic igneous rocks are LILE-rich, HFSE-depleted, with high Sr and Y contents showing typical of normal arc magma affinity. Moreover, the depleted ε Hf (t) (>2.10) and positive ε Nd (t) (>5.7), combined with variable Nb/Ta ratios (9.52–21.4), Y/Nb ratios (1.47–39.7) and Pb isotopes ( 206 Pb/ 204 Pb = 16.225–17.640, 207 Pb/ 204 Pb = 15.454–15.520, 208 Pb/ 204 Pb = 37.097–38.025) suggest that these rocks were magma mixing products between juvenile crustal-derived magmas and minor mantle-derived magmas. Combined published works with our new ages, geochemical and isotopic data, we propose that the Aqishan-Yamansu belt was an Early Carboniferous fore-arc basin during the southward subduction of the Kangguer oceanic slab beneath the Yili-Central Tianshan block. With the continuing southward subduction, the Aqishan-Yamansu fore-arc basin initiated to close, which generated the mafic and intensive intermediate–felsic magmatism associated with regional Fe (–Cu) mineralization. [ABSTRACT FROM AUTHOR]

The Mahoor Cu–Zn-bearing porphyritic granitoid rocks belong to the Lut Block volcanic–plutonic belt (central Eastern Iran). These granitoid rocks occur mainly as dykes and stocks that intrude into Eocene volcanics and pyroclastic rocks. Petrographically, all the studied intrusives display porphyritic textures with mm-sized phenocrysts, most commonly of plagioclase and hornblende, embedded in a fine-grained groundmass with variable amounts of plagioclase, hornblende, clinopyroxene, quartz and opaque minerals. Hydrothermal alteration affected these granitoid rocks, as revealed by the common occurrence of sericite, chlorite, titanite, epidote and calcite. Chemical classification criteria show that the intrusives may be named as gabbrodiorites, diorites, monzodiorites and tonalites. Major elements geochemistry reveals that all the studied lithologies are typically metaluminous (A/CNK ⩽ 0.9). Magnetic susceptibility (1485 × 10 −5 SI) together with mineralogical and geochemical features shows that they belong to magnetite granitoid series (I-type). Trace element patterns normalized to chondrite and primitive mantle are very similar to each other and show enrichments in LREE relative to HREE and in LILE relative to HFSE, as well as negative anomalies of Ta, Nb and Ti. Eu/Eu ∗ ratios vary from 0.88 (in the most mafic composition) to 0.65, showing that plagioclase played a role in magma differentiation. LA-MC-ICP-MS U–Pb zircon data from a diorite, yielded similar concordia ages of ca. 31.88 ± 0.2 Ma (Error: 2 σ ), which corresponds to the Oligocene period. These granitoid rocks have ( 87 Sr/ 86 Sr) i values vary between 0.7055 and 0.7063. In terms of isotopic compositions, while εNdi is between −0.6 and −2.5, suggesting that magmas underwent contamination through being exposed to the continental crust. The whole set of geochemical data agree with the emplacement of the studied intrusions in a magmatic belt above a subduction zone. Primitive magmas should have formed by melting of mantle wedge peridotite, and during magma ascent to crustal levels, both magma differentiations took place by crystal fractionation and crustal contamination. Sulfide mineralizations (pyrite, chalcopyrite and sphalerite) related to these granitoid rocks is common and occurs as both disseminated and hydrothermal veins, indicating a high mineralization potential for this area. [ABSTRACT FROM AUTHOR]

The Mongol–Okhotsk belt and adjacent areas are key areas to study the relationship between the Okhotsk and Paleo-Pacific tectonic regimes and their superposition on the older Paleo-Asian regimes during late Mesozoic times. This paper summarizes the spatial–temporal evolution of Late Mesozoic (Jurassic–Cretaceous) granitoids and related intrusions in these areas, and interprets the magmatic evolution in terms of a transition from contractional crustal thickening to extensional thinning. According to 407 published zircon ages, these granitoids were mainly emplaced during the intervals 200–180 Ma, 180–165 Ma, 165–145 Ma, 145–135 Ma and 135–100 Ma. Jurassic granitoids (200–145 Ma) predominately occur in the Baikal–NE Mongolia (BNEM) and Great Xing’an Range. Early Cretaceous (145–100 Ma) granitoids are mainly occur in the Great Xing’an Range, and display a southward-younging migration. Significantly, Early Cretaceous granitoids also extend into the Trans-Baikal area across the Mongol–Okhotsk suture, far away from the Paleo-Pacific plate margin (in NE China); thus they were more plausibly related to post-orogenic collapse of the Mongol–Okhotsk orogen. From the Late Jurassic to Early Cretaceous, the granitoids evolved compositionally from calc-alkaline and high-K calc-alkaline, I-type, with some adakite-like features, to high-K calc-alkaline and shoshonitic, highly fractionated I-, transitional I-A or, A-type, characterized by a significant decrease in their Sr/Y ratios. This evolution coincided with a tectonic transition from contractional crustal thickening to extensional thinning. Combined with regional geology, we speculate that the Jurassic granitoids were likely derived from melting of the deep-seated, thickened lower continental crustal (LCC) sources, whereas the Cretaceous granitoids produced through crustal melting from an extensional thinning setting. Our results provide a case study demonstrating that the petrogenesis of granitic magmatism was closely associated with crustal tectonics. Early Jurassic granitoids along the Okhotsk belt formed in a subduction/collision setting related to closure of the Mongol–Okhotsk Ocean, whereas Late Jurassic granitoids in the Great Xing’an Range and in the northern North China Craton may have formed in a syn- or post-collisional setting superposed by far-field affects of subduction of the Paleo-Pacific plate. Early Cretaceous granitoids in these areas formed in response to post-orogenic extensional collapse of the Mongol–Okhotsk belt, coupled with back-arc extension related to Paleo-Pacific plate subduction. [ABSTRACT FROM AUTHOR]

Abstract: The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U–Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979–711Ma), Paleozoic (507–400Ma), and Early (252–185Ma) and Late (158–100Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979–911Ma, weakly deformed I-type granites at 894–815Ma, and A-type granites at 759–711Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507–470Ma, 460–422Ma and ∼415–400Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507–470Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460–422Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ∼415–400Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185Ma, with the cluster in 225–200Ma. It took place predominantly in the western part of the South Qinling Belt. The 250–240Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction of the Mianlue Ocean between the South Qinling Belt and the South China Block. Voluminous late-stage (225–185Ma) magmatism evolved from early I-type to later I-A-type granitoids associated with contemporaneous lamprophyres, representative of a transition from syn- to post-collisional setting in response to the collision between the North China and the South China blocks. Late Mesozoic (158–100Ma) granitoids, located in the southern margin of the North China Block and the eastern part of the North Qinling Belt, are characterized by I-type, I- to A-type, and A-type granitoids that were emplaced in a post-orogenic or intraplate setting. The first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process. These suggest that the tectonic evolution of the Qinling Orogen is very complicated. [Copyright &y& Elsevier]

Abstract: Granitic intrusions in Eocene and post-Eocene volcanic rocks outcrop in the Northern and Southern Zones of the Eastern Pontides, NE Turkey. Intrusions in the Northern Zone extend NW–SE whereas those in the Southern Zone are nearly E–W orientated. The contacts of the intrusions with the volcanic rocks are sharp, epidotized and include volcanic xenoliths. The margins of Southern Zone intrusions often contain abundant angular mafic microgranular enclaves of diorite to quartz diorite composition. The rocks also show evidence of mingling and mixing between coeval mafic and felsic magmas. Field observations suggest a stopping type of ascent and emplacement style for the intrusions. Petrographically, intrusions show variations in both colour and mineralogy with fine to medium granular, monzonitic, poikilitic, rapakivi, anti-rapakivi and graphic textures. Based on modal mineralogy, the Northern rocks are monzonite, quartz monzonite, monzodiorite and quartz monzodiorite whereas the Southern samples are monzogranite and granodiorite. The rocks are generally calc-alkaline to mildly alkaline transitional and metaluminous, and show a CAFEMIC trend. The Northern Zone intrusions form a post-collisional, A-type, alkaline monzonitic association and Southern Zone intrusions form a post-collisional, I-type, granodioritic calc-alkaline-transitional association. Whole-rock compositional data indicate that differentiation occurred via fractional crystallisation with or without magma mixing. Incompatible and rare earth element patterns indicate that both the Northern and the Southern Zone intrusions were derived from melting of a mantle region enriched by subduction-related fluids but evolved differently during ascent and emplacement. U–Pb zircon dating in the Southern Zone yields an intrusion age of 44.4±0.3Ma. Regional geodynamics indicates post-collisional extensional tectonics in the region. Crustal involvement and the level of emplacement may have been important for magmatic evolution, especially for the Southern Zone intrusions, after the cessation of subduction and subsequent crustal thickening. [Copyright &y& Elsevier]