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K‐rich adakite‐like rocks (KARs) in post‐collisional settings, such as in Tibet, have been widely linked with the melting of pre‐existing thickened crust. Here, we investigate geochemical data of the Late Eocene (38–34 Ma) volcanic rocks including KARs from the southern Qiangtang terrane (SQT) of central Tibet. The data reveal that: (a) the volcanic rocks define a fractionation trend from high‐K alkaline basalt to high‐K calc‐alkaline rhyolite, with a continuous compositional range and (b) they are characterized by a narrow range of depleted Sr–Nd isotopic compositions relative to the pre‐Eocene SQT crust. We contend that the KARs in the SQT resulted from fractional crystallization of hydrous, alkaline melts derived from the lithospheric mantle where fractionation was dominated by amphibole and plagioclase. Partial melting of the lithospheric mantle beneath the SQT was possibly triggered by thermal perturbations owing to the north‐directed subduction of the Indian continental lithosphere beneath southern Tibet. Plain Language Summary: Adakites were originally defined as silica‐rich magmas produced by melting of basalts in subducting oceanic crust. They are Na‐rich with low K2O and K2O/Na2O, and are characterized by high Sr/Y and La/Yb and low Y and Yb. In post‐collisional settings, such as in Tibet, silica‐rich magmatic rocks with high Sr/Y and La/Yb have been identified, but they are not sodic as true adakites, and are rich in K2O, forming K‐rich adakite‐like rocks (KARs). They have been linked with the melting of pre‐existing crustal rocks at high pressures where garnet is present. We investigate geochemical data of the Late Eocene (38–34 Ma) volcanic rocks that include KARs from the southern Qiangtang terrane (SQT) of central Tibet. We conclude that these KARs were not products of crustal melting at high pressures, but resulted from extreme fractional crystallization of lithospheric mantle‐derived, hydrous, primitive alkaline melts. Given that extreme fractional crystallization commonly occurs in a compressive regime, we argue that the lithospheric mantle underneath the SQT underwent melting during a compressive regime possibly due to thermal perturbations, driven by north‐directed subduction of the Indian continental lithosphere beneath southern Tibet. Key Points: Late Eocene K‐rich adakite‐like rocks (KARs) in the S. Qiangtang terrane resulted from fractional crystallization of a primitive alkaline meltFractionation was dominated by amphibole and plagioclaseKARs from the S. Qiantang terrane have a different origin from those of the Lhasa terrane [ABSTRACT FROM AUTHOR]

Collision‐related porphyry Cu deposits (PCDs) are restricted to previous magmatic arcs, in which sulfide‐rich lower crust occurred. Fertile adakite‐like porphyries associated with PCDs have higher K2O contents and K2O/Na2O ratios than barren porphyries emplaced in the same arc. The elevated K2O/Na2O ratios of fertile porphyries reflect substantial inputs of coeval hydrous, oxidized ultrapotassic melts. Input of such melts could increase the water content and oxygen fugacity of the lower‐crust‐derived melts, which in turn would promote the breakdown of sulphides in the lower crust and increase the contents of Cu and S in the melts, making them favourable for the formation of large PCDs. The relatively low K2O contents and K2O/Na2O ratios of barren porphyries indicate limited input of ultrapotassic melts; these magmas have low potential to form PCDs. Thus, the input of ultrapotassic melts into the sulfide‐rich juvenile lower crust drives the formation of collision‐related PCDs. [ABSTRACT FROM AUTHOR]

The Damoqujia gold deposit in the Jiaodong Peninsula in eastern China contains more than 60 t of gold and is hosted mainly by Mesozoic granitoids. The orebodies comprise pyrite–sericite–silica altered rocks and exhibit Jiaojia‐type mineralization. Although the Damoqujia deposit is an important gold producer in the Zhaoping Fault Zone, the age and tectonic setting of metallogenesis are poorly constrained. Here, we employ precise U–Pb dating of zircon and 40Ar/39Ar dating of hydrothermal sericite from the Damoqujia gold deposit to constrain the age of mineralization, which we integrate with previous studies to understand the tectonic setting of the deposit. The major intrusions exposed in the deposit are the Jurassic monzogranite to the west and the Cretaceous granodiorite to the east. Uranium–Pb dating of zircon from the monzogranite, granodiorite, pre‐ore hydrothermally altered lamprophyre dyke, and post‐ore unaltered gabbro–diorite dyke yield concordia ages of 160 ± 1, 130 ± 1, 125 ± 1, and 120 ± 1 Ma, respectively. Based on these geochronological data, we suggest that the age of gold mineralization at Damuqujia occurred at 124–121 Ma. Sericite from the auriferous quartz–pyrite veinlet in the Damoqujia deposit yields a plateau age of 122.8 ± 0.9 Ma, representing the precise age of gold mineralization. Our geochronological data indicate that gold mineralization occurred at 123 Ma and are consistent with the timing of the main gold mineralization event in the Jiaobei Terrane at 125–120 Ma. The geodynamic setting of the study area during this time is generally considered to have been dominated by subduction of the Palaeo‐Pacific Plate beneath the Eurasian continent, with accompanying lithospheric delamination, asthenospheric upwelling, and intense craton destruction. The gold mineralization at Damoqujia was closely associated with continental extension during the Mesozoic. [ABSTRACT FROM AUTHOR]

The Xiadan gold deposit from Jiaodong Peninsula contains more than 200 t of gold, and is one of the representative largest deposits within south part of the Zhaoping Fault zone. The gold orebodies consist of auriferous altered rocks that show disseminated and stockwork mineralization. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault. Mineralization can be divided into three stages: (K-feldspar)-sericite-quartz-pyrite, quartz-gold-polymetallic sulfide, and quartz-carbonate, with the majority of the gold being produced during the middle stage. Based on a combination of petrography, microthermometry, and laser Raman spectroscopy, three types of fluid inclusion were identified in the vein mineral assemblages: NaCl-H2O (A-type), CO2-H2O-NaCl (AC-type), and pure CO2 (PC-type). Quartz crystals in veins that formed during the early stage contain mainly AC-type primary fluid inclusions, with rare PC-type inclusions. These fluid inclusions homogenize completely at temperatures of 253°C-408°C and have medium-low salinities (1.62-11.89 wt.% NaCl equivalent). Quartz crystals that formed during the middle stage contain all three types of fluid inclusion, and these fluid inclusions homogenize completely at temperatures of 176°C-335°C and have salinities of 0.70-14.73 wt.% NaCl equivalent. In contrast, quartz that formed during the last stage contains only A-type fluid inclusions; these inclusions have homogenization temperatures of 108°C-253°C and salinities of 1.73-11.60 wt.% NaCl equivalent. The above data indicate that the ore-forming system evolved from a CO2-rich mesothermal fluid into a CO2-poor fluid as a result of an influx of meteoric water. Fluid immiscibility is an essential prerequisite for metals precipitation in Xiadian. The characteristics of fluid inclusions, combined with H-O-S isotopes suggest that the ore-forming fluids might be of metamorphic origin. Based on the immiscibility of AC-type fluid inclusions, trapping pressures have been estimated at 88-339 MPa during ore formation, with a depth of metallogenesis of 8.8-12.6 km. The depth of erosion of study area has been calculated as about 10.3 km between 130 Ma and the present. Considering the gold mineralization occurred at around 130 Ma, the space with deep gold exploration is expectable at Xiadian. [ABSTRACT FROM AUTHOR]

The voluminous Eocene postcollisional potassium‐rich magmatism in central Tibet is crucial in understanding the deep geodynamic process and related uplift history of the Tibetan Plateau. Here, we present an integrated study of whole‐rock Sr‐Nd‐Mg‐Li isotopes and zircon U‐Pb ages on two suites of lavas from Duocaima and Nariniya in the northern Qiangtang block. The Duocaima high‐K calc‐alkaline trachyandesites were formed at ~35 Ma and are enriched in light rare earth elements and large ion lithophile elements. They have slightly lower δ26Mg (−0.41‰ to −0.33‰) and δ7Li (+1.0‰ to +2.6‰) relative to the mantle. Together with their high 87Sr/86Sr(i) (0.7066–0.7067) and low ɛNd(t) (−1.96 to −1.61) values, they most likely originated from the lithospheric mantle previously metasomatized by melts from subducted carbonate‐bearing sediments. Model calculation suggests that ~7–11% sediments were added into the mantle via melting. By contrast, the contemporaneous Nariniya adakitic trachytes have higher δ26Mg (−0.13‰ to −0.02‰) and δ7Li (+3.3‰ to +5.4‰) values, as well as higher Pb/Ce and Ba/La ratios, which most likely resulted from the thickened lower crust that was metasomatized by fluids released from downgoing Songpan‐Ganzi oceanic slab. Our combined isotopic study suggests the existence of a remnant oceanic slab beneath central Tibetan Plateau during the late Eocene and implies that the initial uplift of central Tibet was before ~38 Ma. Key Points: Highly variable Mg and Li isotopes in potassium‐rich volcanic rocks from Qiangtang resulted from subducted slab inputsAn ancient remnant oceanic slab still existed beneath central Tibet during the late EoceneThe initial uplift of central Tibet was before ~38 Ma [ABSTRACT FROM AUTHOR]