Mesozoic Granitic Magmatism Research Articles

Two episodes of Mesozoic granitic magmatism in East Qinling, central China: Constraints from geochemistry and isotope geochronology of the Huangbeiling pluton

The East Qinling Orogen as an important segment of central China that records a complex tectonic evolution history. The Huangbeiling pluton is a rare S-type granite in this orogen and has vital significance in understanding the tectonic evolution of the Qinling Orogen during the Late Mesozoic. The biotite monzogranite of this pluton is the major ore-hosting rocks of the Yumugou Mo-W deposit. In this study, we newly reported a muscovite monzogranite and conducted detailed petrological, geochemical (whole-rock, biotite, muscovite major and trace elements), and zircon U-Pb dating investigations on both the biotite and muscovite monzogranites from the Huangbeiling pluton, with a view to reveal their physico-chemical conditions of formation, petrogenesis and tectonic evolution. Zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 126.8 ± 0.6 Ma for muscovite monzogranite, integrated with published zircon U-Pb age (156–132 Ma) of biotite monzogranite, indicating that the Huangbeiling pluton was produced by two episodes of magmatism during the Late Mesozoic. The pluton shows formation temperatures in the range of 670–772°C, and is classified as cold granites that formed in a subduction-related setting. The emplacement depth of Huangbeiling pluton is constrained at ca. 0.3–4.6 km, with an average depth of 2.0 km. The biotite monzogranite has higher oxygen and fluorine fugacities than the muscovite monzogranite, suggesting high potential for Mo mineralization. Geochemically, the muscovite monzogranite is identified as a S-type granite sourced from crust-derived clay-rich mudstone, and underwent muscovite dehydration melting and subsequent fractional crystallization of K-feldspar and plagioclase during magma ascend. In combination with the syn- to post-collision geochemical affinities of the Huangbeiling pluton and the Late Mesozoic tectonic evolution of the Qinling Orogen, we propose two episodes of magmatism in the Huangbeiling pluton during the tectonic transition (150–125 Ma) from compression to extension in the Qinling Orogen. The first episode (156–132 Ma) of magmatism is correlated with the delamination of lithospheric mantle and intra-continental subduction of the North China Craton under compressional tectonics, whereas the second episode (∼126 Ma) of magmatism occurred through muscovite dehydration melting during pressure decrease.

Genetic link between the Late Mesozoic granitic magmatism and W mineralization in NE China: Constraints from in-situ U-Pb geochronology and geochemistry of wolframite, and whole-rocks geochemistry analyses of W-bearing granites from the Sansheng W-Mo deposit

The Sansheng quartz-vein type W-Mo deposit is located on the southern margin of NE China. Tungsten mineralization occurs mainly in veins and veinlets within the Early Cretaceous granitic pluton. In-situ U-Pb dating of hydrothermal wolframite yields a W mineralization age of 137.3 ± 2.0 Ma (1σ, MSWD = 4.4), which provides evidence for an Early Cretaceous W mineralization event in the Sansheng area. W-bearing granites show petrological, mineralogical, and geochemical characteristics of highly fractionated A-type granites. The rocks belong to the high-K calc-alkaline series and are characterized by the enrichment in large ion lithophile elements (e.g., Rb, Th, U, and K) and significant negative Eu, Ba, Sr, P, and Ti anomalies. They also have higher W concentrations, Rb/Sr and U/Th ratios, and lower (La/Yb)N, LREE/HREE, Eu/Eu*, K/Rb, Zr/Hf, Nb/Ta, and Y/Ho ratios than the contemporary W-barren granitoids in NE China. The geochemical signatures of the W-bearing granites indicate that the primary magmas were derived from partial melting of the lower crust and subsequently underwent extensive fractional crystallization. The W mineralization in the Sansheng is genetically related to the W-bearing granites, and extreme fractional crystallization was critical for W enrichment in granitic magma. The trace element compositions of the wolframite show similar enrichments in HREEs, Nb, Ta, and U, as well as depletion in LREEs, Rb, Ba, Th, Pb, Sr, and Ti, compared to those of the upper continental crust. We demonstrate that isovalent substitution mechanisms could have played critical roles in the formation of hydrothermal wolframite in the Sansheng deposit, and the chemical composition of wolframite is controlled by both the crystallochemical parameters and composition of the primary hydrothermal fluids. In the context of the regional geology, the new data suggest that the Sansheng W-bearing granites and corresponding mineralization formed in a post-collisional extensional setting controlled by the closure of the Mongol-Okhotsk Ocean and the rollback of the Paleo-Pacific Ocean plate during the Early Cretaceous.

Geochemistry and Zircon U–Pb Geochronology of the Zhuxi Granites in the Jingdezhen Area, Jiangxi Province, China: Implications for the Mesozoic Tectonic Development of South China

Mesozoic granitic magmatism in Northeastern Jiangxi, China is of tectonic significance for the evolution of the South China Block. Whole-rock geochemical and zircon U–Pb geochronological and Lu–Hf isotopic data for Mesozoic Zhuxi granites in the Jingdezhen area of Northeastern Jiangxi were presented. The Zhuxi granites are composed of granodiorite, biotite granite, and two-mica granite. Zircon LA–ICP–MS U–Pb isotopic analyses indicated emplacement at 159–147 Ma. The granites are characterized by a strongly peraluminous nature with high A/CNK values (>1.1), high SiO2 (66.09–74.46 wt.%) and K2O (3.50–5.52 wt.%) contents, depletion in Ba, Nb, Ce, Sr, and Ti, moderately negative Eu anomalies (Eu/Eu* = 0.40–0.63), enrichment in LREE, and depletion in HREE ((La/Yb)N > 7.43). The A/CNK > 1.1, widespread aluminum-rich minerals (e.g., muscovite and tourmaline), indicating they are S–type granites and belong to muscovite–bearing peraluminous granites (MPG). The Zhuxi granites exhibited negative εHf(t) values (−9.9 to −3.7) and the TDM2 model ages of 1840–1442 Ma indicated derivation from ancient crustal sources. The magma is possibly caused by the subsequent process of intracontinental subduction. It is inferred that the Mesozoic magmatism in Northeastern Jiangxi was associated with oceanic–continental convergence of the Paleo–Pacific and Eurasian plates as well as the intracontinental subduction of the Yangtze and Cathaysia blocks. The Zhuxi granites highlight the primary role of oceanic–continental convergence and intracontinental subduction in early Yanshanian granitoid magmatism in South China.

Influence of fluid-rock interaction on gold mineralization in the Dongwan deposit, East Qinling, China: Constraints from systematic sulfur isotope and trace element geochemistry

The Dongwan gold deposit is located in the Xiong'ershan area, East Qinling, China, with gold ore bodies hosted in NE-trending hydrothermal alteration zone and quartz + sulfides veins in structures. Here we present systematic field investigation, petrographic observations, in-situ trace elements and sulfur isotope of pyrite, and sulfur isotope of galena and barite to elucidate the genesis and effect of fluid-rock interaction during hydrothermal evolution of the Dongwan gold deposit. Four types of pyrite are recognized based on their occurrences in different hydrothermal veins, structures and paragenetic sequences, as follows: i) Py1 in the stage I quartz-pyrite vein is composed of coarse-grained cubic pyrite (Py1-1) and medium-grained cubic pyrite (Py1-2); ii) Py2 is characterized by fine-grained disseminated pyrite in stage II vein; iii) Py3 is represented by pyrite that occurs together with galena, sphalerite and chalcopyrite in stage III vein. The early stage Py1-1 and Py1-2 are characterized by high Co/Ni ratios and low contents of As, Au and Ag. The main ore-forming stages represented by Py2 and Py3 show lower Co/Ni ratios and higher concentrations of As, Sb, Au, Ag, Pb and Cu. The Ni contents of all pyrite types are < 10 ppm, indicating that the ore-forming fluid was derived from felsic rocks. The δ34S values of the different pyrite generations range between −16.0‰ and −7.4‰, which are attributed to the fractionation between barite and sulfide minerals. The sulfur isotopic composition of the hydrothermal fluid calculated from co-genetic barite and pyrite is 1.2‰, suggesting that the ore-forming materials were possible derived from mantle source, and were correlated with the Late Mesozoic granitic magmatism. The main mechanisms of gold precipitation are fluid-rock interaction and decrease of temperature, which promote the Fe2+ rich Xiong’er Group wall rocks to reduce the hydrothermal fluid and disequilibrate the gold-sulfur complex causing the precipitation of gold. The overall trace elements and sulfur isotopic signatures suggest that the pyrite is of magmatic-hydrothermal origin, and that the ore-forming materials of the Dongwan gold deposit are probably related to post-magmatic fluids derived from the Early Cretaceous granitoid magmatism in the region.

Distal gold mineralization associated with porphyry system: The case of Hongzhuang and Yuanling deposits, East Qinling, China

The Hongzhuang and Yuanling gold deposits are located in the Shiyaogou ore field within the Xiong'ershan area, East Qinling, China, where the ore bodies are hosted in Xiong'er Group and mainly controlled by EW-trending and NE-trending faults. The gold mineralization mechanism and the possible genetic link with the porphyry magmatism and hydrothermal events remain unclear. Here we present results from systematic field investigation, petrographic observation, in situ trace elements and sulfur isotope of pyrite to elucidate the genesis of gold mineralization in these deposits. Based on the occurrences of pyrite in different hydrothermal veins, three types of pyrite are identified from each deposit, including: i) coarse-grained cubic pyrite (HZ-Py1 and YL-Py1) in stage I milky quartz vein; ii) medium- to fine-grained pyrite (HZ-Py2 and YL-Py2) in stage II polymetallic sulfides veins; iii) coarse-grained pyrite (HZ-Py3 and YL-Py3) symbiotic with calcite in stage III quartz-calcite vein. The LA-ICP-MS trace element analyses of pyrite show that Au occurs as invisible nanoparticles or nano-sized inclusions in pyrite through absorption-chemisorption during the growth of pyrite or as nano-sized Au-bearing mineral inclusions. The δ34S values of different generations of pyrite in the Hongzhuang and Yuanling gold deposits range from 3.92‰ to 6.43‰ and 2.82‰ to 4.46‰, respectively, indicating that the ore-forming materials were mainly derived from mantle-related source with affinity to the Late Mesozoic granitic magmatism. The Hongzhuang and Yuanling gold deposits are spatially and temporally correlated with the Shiyaogou pluton and they show consistent material sources. We propose that the hydrothermal Au mineralization in these deposits were the distal products generated from the post-magmatic fluids of the Shiyaogou porphyry system. The stretching and thinning of the early Cretaceous lithosphere led to the upwelling of magma and migration of fluid, forming the Au mineralization in fault structures in the shallow crust.

Two episodic Au–Mo mineralization in the Laowan district from the Tongbai orogenic belt of China: Constraints from U–Pb dating of zircon, rutile, and REE phosphate, and Re–Os dating of molybdenite

The Laowan super-large (208 t Au) gold deposit is located in the Tongbai orogenic belt, along with a newly-discovered molybdenite deposit at its depth in the northern periphery. The gold deposit is a fault-controlled lode gold deposit featuring sulfide quartz vein-type and altered rock-type mineralization hosted within the metamorphic rocks, whereas the molybdenum deposit is a typical porphyry-type deposit. These two deposits have their respective paragenetic sequences and mineralization types without spatial overlapping in the ore field. Here, we present U–Pb dating of zircon, hydrothermal rutile, and REE phosphates, and Re–Os dating of molybdenite to constrain the relationship between the Au and Mo mineralization, and their relation to Mesozoic granitic magmatism. Textural features indicate that rutiles and associated phosphate minerals are of hydrothermal origin, generated by re-precipitation and dissolution of titanite crystals hosted in the metamorphic host rocks due to hydrothermal alteration during Au and Mo mineralization. LA-ICP-MS U–Pb dating of rutile from the auriferous altered rocks yields a 206Pb/238U age of 120.0 ± 6.7 Ma (MSWD = 1.4), consistent with the ages of the associated monazite (125.0 ± 2.4 Ma) and xenotime (126.3 ± 2.0 Ma), representing the timing of the gold mineralization, coeval with Laowan monzogranite (zircon U–Pb: 128.8 ± 0.7 Ma). Rutile from the molybdenum deposit show an older 206Pb/238U age of 141.0 ± 11 Ma (MSWD = 1.1), consistent with the molybdenite Re–Os age (141.5 ± 1.7 Ma; MSWD = 0.27) and the zircon U-Pb age (141.6 ± 0.8 Ma; MSWD = 1.5) of the Songpa porphyry. Hence, the Au and Mo mineralization in the Laowan district represent two episodic mineralization events related to the late Mesozoic granitic magmatism. Our study also suggested that multiple isotopic dating is helpful to precisely constraint the ages for complex hydrothermal deposits.

Early Mesozoic magmatism and tectonic evolution of east-central Tibet

The Early Mesozoic granitoids in the east-central Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study, three stages of Early Mesozoic granitic magmatism were indicated by LA-ICP-MS zircon U–Pb dating on 14 samples. The Early Triassic (248–243 Ma) and the Late Triassic (213–208 Ma) were distributed in the North Qiangtang terrane, and the Early Jurassic (ca. 187 Ma) occurred in the Tongka and Jiayuqiao blocks. The Late Triassic and Early Jurassic granitoids show similar negative zircon eHf(t) values (− 5.5 to − 16.6) with TDM2 model ages of 1.60–2.28 Ga, suggesting a Paleoproterozoic crustal source, whereas the Early Triassic granitoids have zircon eHf(t) values from − 3.4 to + 5.3 with TDM2 model ages of 0.94–1.50 Ga, indicating a Mesoproterozoic crustal source. Based on the whole-rock geochemical data, we suggest that the Early Triassic rocks from the North Qiangtang terrane include I- and S-type granites and the Late Triassic rocks are S-type granites, which were related to the northward subduction of the Longmu Tso–Shuanghu–Dingqing Paleo-Tethys Ocean and subsequent collision between the North Qiangtang terrane and Tongka block, respectively. The Early Jurassic granitoids from the Tongka and Jiayuqiao blocks also included both I- and S-type granites and were probably generated in an arc-related setting during the northward subduction of the Bangong–Nujiang Tethys Ocean. Therefore, we suggest a collision–accretion model that attributes the Early Mesozoic tectonic-magmatic event to the sequential multistage subduction and collision in the east of central Tibet.

Late Mesozoic felsic magmatism and Mo-Au-Pb-Zn mineralization in the southern margin of the North China Craton: A review

The widespread large-scale Mo-Au-Pb-Zn mineralization in the southern margin of the North China Craton (NCC) is spatially and temporally associated with the voluminous late Mesozoic granitic magmatism. Relationship between the granitic magmatism and ore mineralization has been extensively investigated in the last decade. However, controversy still exists regarding the magma source, metallogeny and geodynamic settings. This paper systematically reviews the major features of the Mesozoic granitic magmatism and associated Mo-Au-Pb-Zn mineralization in the southern margin of the North China Craton, including temporal and spatial variations of magmatic rocks, composition of ore-fluids, sources of ore metals, and metallogeny. The granitic rocks were mainly formed in late Mesozoic and emplaced in two stages. The early-stage (158–128 Ma) granites are of typical I-type derived from remelting of ancient crust of the southern margin of the NCC with input of mantle material under lithospheric thinning tectonic regime. The late-stage (127–112 Ma) granites include A-type and/or highly fractionated I-type granites, which commonly contain more fractions of mantle materials as exhibited by more depleted isotopic signatures, suggestive of an intracontinental extensional setting. Mo mineralization (155–130 Ma) related to the early-stage granitic magmatism includes mainly of porphyry or porphyry-skarn type with ore metals mainly derived from the mixed source of the mantle and crust, whereas the late-stage Mo mineralization (127–116 Ma) is mainly of porphyry type with the ore metals from similar sources with more input of mantle materials. Pb-Zn deposits (144–130 Ma) associated with the early-stage granitic magmatism are mainly of hydrothermal vein and skarn types, whereas those (125–117 Ma) related to the late-stage granites are of hydrothermal vein type. The Pb-Zn deposits are most likely distal products of the Mo deposits, together forming a metallogenic system. Au deposits are located in the Xiaoqinling and Xiong’ershan areas, and were formed during Middle Jurassic to Early Cretaceous (163–118 Ma) mostly from 132 to 120 Ma. The ores mainly occur in quartz veins and altered rocks and are hydrothermal magmatic in origin with Au derived from a mixed source of crust and mantle.

Petrogenesis of ore-forming granites with implications for W-mineralization in the super-large Shimensi tungsten-dominated polymetallic deposit in northern Jiangxi Province, South China

The Shimensi deposit is a newly discovered, super-large tungsten (W) polymetallic deposit in northwestern Jiangxi Province, South China. In this paper, we reported new zircon U–Pb ages for the ore-bearing porphyritic biotite granite (151.3 ± 2.8 Ma) and fine-grained granite (150.1 ± 1.2 Ma and 150.7 ± 2.4 Ma), which represent the oldest Mesozoic granitic magmatism reported at Shimensi. Our ore-bearing granite porphyry ages (142.7 ± 2.3 Ma and 143.3 ± 1.5 Ma) have better constrained the timing of the Jurassic-Early Cretaceous ore-forming magmatism. Geochemically, the Shimensi granitoids are strongly peraluminous, with high contents of SiO2 (70.7–78.7 wt%) and K2O (>4.0 wt%), P2O5, Rb, Ta and U, and low contents of Ti, Sr, Ba and HREEs. The rocks also show positive P2O5 vs. SiO2 correlation, suggesting a highly-fractionated S-type affinity. Different from most W-bearing granites in the Jiangxi region, the calculated zircon εHf(t) (−10.0 to −2.4; two-stage model ages: 1350–1824 Ma) and δ18Ozircon values (+6.40 to +8.87‰) of the Shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks, probably with combined contributions from the Neoproterozoic Shuangqiaoshan Group metamorphic rocks and Jiuling granodiorite. The calculated zircon Eu/Eu∗ (0.05–0.58; mean = 0.20) and Ce4+/Ce3+ (3.83–96.49; mean = 20.99) ratios of the granites indicate very low oxygen fugacity (fO2) for the ore-forming magmas, a highly favorable factor for W mineralization. Potentially W and Cu-rich source rocks, and highly-fractionated and reducing granitic magmas, were important factors that triggered super-large W mineralization at Shimensi.

Late Mesozoic magmatism and tectonic evolution in the Southern margin of the North China Craton

Late Mesozoic granitic magmatism (158–112 Ma) are widespread in the southern margin of the North China Craton (NCC), contemporary with many world-class Mo-Au-Ag-Pb-Zn polymetallic deposits. There are abrupt changes in the elements and isotopic compositions of these granites at about 127 Ma. The early stage (158–128 Ma) granites show slightly or no negative Eu anomalies, large ion lithophile elements enriched and heavy REE depleted (such as Y and Yb), belonging to typical I-type granite. The late stage (126–112 Ma) granites are characterized by A-type and/or highly fractionated I-type granite, with higher contents of SiO2, K2O, Y, Yb and Rb/Sr ratio and lower contents of Sr, δ Eu value and Sr/Y ratio than that of the early-stage granites. Moreover, the whole rock Nd and Hf isotopic compositions of the granites younger than 127 Ma show more depleted than those of the older one. The two stages of Late Mesozoic granites were derived from a source region of the ancient basement of the southern margin of the NCC incorporated the mantle material. The late stage (126–112 Ma) granites contain more fractions of mantle material with depleted isotopic composition than the early ones. The granites record evidence for a strong crust-mantle interaction. They formed in an intracontinental extensional setting which was related to lithospheric thinning and asthenospheric upwelling in this region, which was possibly caused by westward subduction of the Paleo-Pacific plate. 127 Ma is an critical period of the transformation of the tectonic regime.

The genesis of the Hashitu porphyry molybdenum deposit, Inner Mongolia, NE China: constraints from mineralogical, fluid inclusion, and multiple isotope (H, O, S, Mo, Pb) studies

The Hashitu porphyry molybdenum deposit is located in the Great Hinggan Range Cu-Mo-Pb-Zn-Ag polymetallic metallogenic province of NE China, in which the Mo-bearing quartz veins are hosted in approximately coeval granites and porphyries. The deposit contains more than 100 Mt of ore with an average grade of 0.13 wt.% Mo. This well-preserved magmatic-hydrothermal system provides an excellent opportunity to determine the source of the molybdenum, the evolution of the hydrothermal fluids and the controls on molybdenite precipitation in a potentially important but poorly understood metallogenic province. Studies of fluid inclusions hosted in quartz veins demonstrate that the Hashitu hydrothermal system evolved to progressively lower pressure and temperature. Mineralogical and fluid inclusion analyses and physicochemical calculations suggest that molybdenite deposition occurred at a temperature of 285 to 325 °C, a pressure from 80 to 230 bars, a pH from 3.5 to 5.6, and a ∆log fO2 (HM) of −3.0, respectively. Results of multiple isotope (O, H, S, Mo, and Pb) analyses are consistent in indicating a genetic relationship between the ore-forming fluids, metals, and the Mesozoic granitic magmatism (i.e., δ 18OH2O from +1.9 to +9.7‰, δDH2O from −106 to −87‰, δ 34SH2S from +0.3 to +3.9‰, δ 98/95Mo from 0 to +0.37‰, 206Pb/204Pb from 18.2579 to 18.8958, 207Pb/204Pb from 15.5384 to 15.5783, and 208Pb/204Pb from 38.0984 to 42.9744). Molybdenite deposition is interpreted to have occurred from a low-density magmatic-hydrothermal fluid in response to decreases in temperature, pressure, and fO2.

Geochronology and Petrogenesis of Mesozoic Granitoids in the Geological Corridor of Western Liaoning Province, China

Geochronology and Petrogenesis of Mesozoic Granitoids in the Geological Corridor of Western Liaoning Province, China

Late Cretaceous granites from the giant Dulong Sn-polymetallic ore district in Yunnan Province, South China: Geochronology, geochemistry, mineral chemistry and Nd–Hf isotopic compositions

As a world-class tin–tungsten province, South China is well known for its extensive Mesozoic granitic magmatism. The Dulong district, located in the western Cathaysia Block of the South China tin–tungsten province, is characterized by widespread Mesozoic granitoids and accompanying Sn-polymetallic ore deposit (~30 Mt of Sn). It is one of the most important polymetallic tin ore districts in China. In this study, three mineralization-related granite types were identified in the Dulong district, including the Dulong coarse-grained granite (DCG), the Dulong fine-grained granite (DFG), and the Dulong porphyritic granite (DPG). Detailed studies are presented on zircon U–Pb ages, major and trace elements, mineral chemical and Nd–Hf isotopic compositions of the tin-bearing granites from the Dulong district. LA-ICP-MS U–Pb dating of zircon grains from these three granite bodies yields ages of 90.1±0.7Ma, 89.7±0.8Ma and 86.0±0.5Ma, respectively. Geochemically, the granites are strongly peraluminous, with high contents of alkalis, enrichment in P, Li, Rb, Cs, Ta, Sn, W and U, depletion in Ti, Mg, Co, Ni, Sr, Ba, Zr, Hf, Th and rare earth elements. Fractional crystallization of plagioclase and K-feldspar was the principal process of magmatic differentiation that controlled Rb, Sr, Ba and Eu concentrations, whereas rare earth elements were fractionated by accessory minerals, such as apatite and monazite. The geochemical data suggest that the rocks are highly fractionated S-type granites. The granites show bulk rock εNd(t) values in the range of −12.2 to −10.8 and zircon εHf(t) values from −15.5 to −2.5, with Meso-Paleoproterozoic TDMC ages for both Nd and Hf isotopes. Geochemical and isotopic data suggest that these highly fractionated S-type granites DCG, DFG and DPG were originated from the same episode of partial melting of the protolith, which have analogous components of metamorphosed pelitic rocks from the Meso-Paleoproterozoic continental crust. Extreme fractional crystallization resulted in enrichment of tin in the evolved granitic magma, and the reduced magmas (fO2 below NNO) would efficiently remove Sn into a hydrothermal fluid, and lead to deposition of Sn-rich mineral phases. The association of Dulong and Gejiu magmatism in the western Cathaysia Block may be likely to mark the onset of back-arc extension or intra-arc rift in the region during Late Cretaceous. The upwelling of asthenospheric mantle may have triggered partial melting of metasedimentary rocks in the overlying crust to generate the S-type granitic magmas.

Genetic relationship between silver–lead–zinc mineralization in the Wutong deposit, Guangxi Province and Mesozoic granitic magmatism in the Nanling belt, southeast China

More than 50 % of the world's total reserves of tungsten are in China and most tungsten deposits are located in the Nanling range in southeast China. This study explores the potential genetic relationship between tungsten–tin (W–Sn) mineralization and shallower Ag–Pb–Zn deposits in the Nanling range based on data from the Wutong deposit, Guangxi Province. The lead, oxygen, carbon, sulfur, and strontium isotopic compositions of minerals at Wutong indicate that a single crustal-derived fluid was responsible for mineralization. Wutong likely formed at relatively low temperatures (∼200–300 °C) and low pressures, as indicated by the similarity between homogenization temperatures of fluid inclusions and those estimated from S isotopic compositions of minerals. The hübnerite age (92.3–104.4 Ma) indicates that the Wutong mineralization is likely related to nearby Late Yanshanian (Cretaceous) S-type granites derived from Proterozoic crust. This mineralization event coincides with the last W–Sn mineralization event and the Cretaceous peak of mineralization in the Nanling range.

Petrogenesis and evolution of late Mesozoic granitic magmatism in the Hohhot metamorphic core complex, Daqing Shan, North China

Late Mesozoic granitoid plutons of four distinct ages intrude the lower plate of the Hohhot metamorphic core complex along the northern margin of the North China craton. The plutons belong to two main groups: (1) Group I, deformed granitoids (148 and 140 Ma subgroups) with high Sr, LREE, and Na2O, low Y and Yb contents, high Sr/Y and La/Yb ratios, weak or no Eu anomalies, low Rb/Ba ratios, similar initial 87Sr/86Sr values (0.7064–0.7071) and low Mg# (<37 mostly, 100 × molar MgO/MgO + FeO t ); (2) Group II, non-deformed granitoids (132 and 114 Ma subgroups) with low Sr, relatively low Na2O, high Y and Yb contents, pronounced negative Eu anomalies, high Rb/Ba ratios, and initial 87Sr/86Sr values (0.7098–0.7161). The two groups share geochemical similarities in ϵNd(t) (–11.3 to –15.4) and T DM2 ages (1.85–2.18 thousand million years) as well as Hf isotopic ratios in zircons. Geochemical modelling (using the MELTS code) suggests that similar sources but different depths of magma generation produced the early, high-pressure low-Mg adakitic granitoids and late, low-pressure granitoids with A-type characteristics. The early granitoids likely represent a partially melted, deep-seated, thickened lower continental crust that involved a minor contribution from young materials, whereas the later group partially melted at shallower depths. This granitic magmatic evolution coincided with the tectonic transition from crustal contraction to extension.

Geochemistry, geochronology and Sr–Nd–Hf isotopes of two Mesozoic granitoids in the Xiaoqinling gold district: Implication for large-scale lithospheric thinning in the North China Craton

The Mesozoic granitoids at the southern margin of the North China Craton are of considerable geologic interest, because of their geodynamic context and likely relationship to Mesozoic lithospheric delamination, but also because they are associated with one of the most important gold belts in China. However, their detailed age relations and petrogeneses have not been described by systematic and comprehensive geochemical studies. Here we report a systematical zircon U–Pb dating, petrogeochemistry, and Sr–Nd–Hf isotopic data on two of these granitoids (namely the Wenyu and the Niangniangshan plutons) in the Xiaoqinling gold district, Henan Province, North China. Both plutons are metaluminous to weakly peraluminous, and can be classified as I-type granites with similar zircon U–Pb ages of 131±1Ma and 134±1Ma. They are enriched in Si, K, Ba, and Sr, while depleted in Nb, Ta, P, Ti, Mg, Ni, V and Y, and both have Archaean-type tonalite–trondhjemite–granodiorite (TTG) and adakitic affinity, e.g. enrichment in LREE with high Sr/Y and La/Yb ratios and without Eu anomalies. Both the plutons show relatively high initial 87Sr/86Sr ratios (0.7076–0.7089 for the Wenyu pluton and 0.7074–0.7086 for the Niangniangshan pluton), negative εNd(t) values (−15.0 to −10.1 for the Wenyu pluton and −18.5 to −12.2 for the Niangniangshan pluton), and negative εHf(t) values (−21.9 to −10.4 for zircons from the Wenyu pluton and −30.8 to −20.8 for zircons from the Niangniangshan pluton). All the isotopic data indicate old crustal sources for the magma. Furthermore, low concentrations of MgO, Ni, and V also indicate little or no mantle materials in the source. The local Neoarchaean to Palaeoproterozoic basement rocks are the most likely sources, but their isotopic compositions do not cover the total isotopic range of the plutons, hence there maybe other sources involved. The occurrence of 1.78Ga inherited zircon grains on the depleted mantle Hf isotopic evolution line indicates 1.78Ga underplating mafic rocks to be a possible source. Detailed petrologic and geochemical data indicate that the two plutons derived from partial melting of Neoarchaean to Palaeoproterozoic metamorphic rocks and possibly with minor amounts of 1.78Ga mafic lower-crustal rocks at a depth of at least 50km, with eclogite, garnet amphibolite or amphibolite residues. During the magma crystallization stage, amphibole, apatite and titanite fractionation caused the observed variations of the element compositions. Meanwhile, the existence of >50-km-depth crust indicates that large-scale lithospheric thinning in this part of the south margin of North China Craton did not take place prior to the emplacement of these granitoids 130Myr ago. However, a fuller understanding of the geological significance of the widespread occurrence of Mesozoic granitic magmatism in the south margin of North China Craton will require similarly detailed studies of other granitoids in the region. In this way it should be possible to constrain their source compositions and the nature of the heat source(s) that led to this lithospheric thinning event.

Geology and Metallic Mineralization Associated with Mesozoic Granitic Magmatism in South Korea

Geology and Metallic Mineralization Associated with Mesozoic Granitic Magmatism in South Korea

SHRIMP U–Pb Zircon geochronology of the Altai No. 3 Pegmatite, NW China, and its implications for the origin and tectonic setting of the pegmatite

The “Altai No. 3 granitic pegmatite” in NW China is the largest pegmatite in the world that has been found in an orogenic belt; it forms one of the largest muscovite deposits in Asia and is most famous for its concentric-ring structure. Although it has been mined for more than 70 years, the age of formation and mineralization of the pegmatite has not been well determined, despite numerous previous geochronological studies. Here we present new results of SHRIMP U–Pb zircon dating. Three weighted mean 206Pb/ 238U ages of 220 ± 9 Ma, 198 ± 7 Ma and 213 ± 6 Ma were obtained for pegmatite zones 1, 5, and 7, respectively. The analyses were made on clear, recrystallized domains and overgrowth rims of large, opaque high-U zircon grains. We interpret the age of 220 ± 9 Ma for zone 1 to approximately represent the initial time of formation for No. 3 pegmatite. An additional date of 213 ± 2 Ma was determined on zircon from a small subordinate vein formed in the late-stage phase of the No. 3 pegmatite. This age set the late age of emplacement of the pegmatite. The time span of 213 to 198 Ma may reflect late stage hydrothermal alteration. In addition, a weighted mean 206Pb/ 238U age of 277 ± 6 Ma was obtained from small, clear, transparent low-U zircon grains which are more probably xenocrysts. Our new age data indicate that the pegmatite has no genetic relationship with the wall granitic rocks (409 Ma), but is likely related to the early Mesozoic (220 Ma) granitic magmatism that was just recognized. The No. 3 pegmatite was formed in an early Mesozoic anorogenic extensional regime. A stable tectonic setting was undoubtedly required for the formation of the large pegmatite.

Geology, fluid inclusions, isotope geochemistry, and geochronology of the Paishanlou shear zone-hosted Gold Deposit, North China Craton

The Paishanlou gold deposit lies along the northern margin of North China Craton gold province, the third largest Au province in China. The deposit is mainly hosted in Archean metamorphic rocks of the Jianping Group and is structurally controlled by two sets of ductile shear zones. Gold mineralization is closely associated with intense hydrothermal alteration along the ductile shear zones, with a typical greenschist facies alteration assemblage of sericite + chlorite + calcite + biotite + quartz and a distinct alteration zoning of inner pyrite-sericite zone, middle carbonate zone, and outer epidote-biotite-chlorite zone from orebody to wall rock. Fluid inclusion petrography and microthermometric results suggest that four types of fluid inclusions are present at the deposit. Type 1 CO 2-rich inclusions have homogenization temperatures of 22.4–27.9 °C. Type 2 H 2O–CO 2 inclusions show salinities of 4.6–12.3 wt.% NaCl equivalent and Th-tot of 242 to 337 °C. Type 3a primary aqueous inclusions have salinities of 5.9–11.2 wt.% NaCl equivalent and Th-tot of 187–289 °C, while Type 3b secondary aqueous inclusions have salinities of 3.1–8.3 wt.% NaCl equivalent and Th-tot of 128–239 °C. Type 4 multiphase inclusions have salinities ranging from 31.4 to 35.2 wt.% NaCl equivalent and Th-tot of 370–447 °C. The close association of CO 2-rich inclusions and H 2O-rich inclusions in groups and along the same trail suggests the presence of fluid immiscibility. Estimated P– T values range from 1.4 to 1.9 kbar at 322–417 °C. The δ 18O values of the ore-forming fluids are calculated to range from 3.8‰ to 7.4‰ and the δD values from − 87.3 to − 116.2‰, indicating a mixed source of deep-seated magmatic water and shallower meteoric water. The δ 34S values (0.3–7.5‰) of sulfide ore minerals are similar to those of both pyrite from metamorphic country rocks and whole rock sulfur of metamorphic country rocks. The 206Pb/ 204Pb, 207Pb/ 204Pb and 208Pb/ 204Pb of sulfide ores range within 16.40–17.0, 15.21–15.37, and 36.69–37.38, respectively, with the model ages of 397–727 Ma, consistent with those of Late Mesozoic granites and lying between Archean metamorphic rock lead and the Proterozoic dolomitic marble lead. These sulfur and lead features reflect the fact that the ore-forming materials originated mainly from multiple wall-rock sources. The well-defined Ar/Ar plateau age (126.6 ± 1.1 Ma) of biotite from the NNE ductile shear zone provides a possible temporal link between Au mineralization, magmatism and deformation at the Paishanlou deposit. The concordance of the biotite age with other well-constrained mineralization ages for the deposit, and the intrusion age of the granite, suggests that Au mineralization was essentially contemporaneous with late Mesozoic granitic magmatism and the second stage of mylonitization. In terms of its genetic linkage with the subduction process at the leading northern edge of the North China Craton, the Paishanlou deposit can be favored as an orogenic gold deposit. Its formation benefited from the combined action of protracted activity of ductile fault zones, hydrothermal circulation associated with granitoid intrusion and preferred structural setting favoring gold deposition. The major geodynamic switch towards generalized extensional tectonics that occurred during uplift, and thinning of the upper crust after the collisional stages in the northern edge of the North China Craton, may be the key factors controlling Au concentration and enrichment in the Paishanlou deposit.

Mesozoic granitic magmatism in extensional tectonics near the Mongolian border in China and its implications for crustal growth

The Yagan area of the southernmost Sino–Mongolian border is characterized by an extensional structure where a large metamorphic core complex (Yagan–Onch Hayrhan) and voluminous granitoids are exposed. New isotopic age data indicate that the granitoids, which were previously regarded as Paleozoic in age, were emplaced in early and late Mesozoic times. The early Mesozoic granitoids have 228±7 Ma U–Pb zircon age, and consist of linear mylonitic quartz monzonites and biotite monzogranites. Their chemical compositions are similar to those of potassic granites and shoshonitic series, and show an intraplate and post-collisional environment in tectonic discrimination diagrams. Their fabrics reveal that they experienced syn-emplacement extensional deformation. All these characteristics suggest that the adjustment, thinning and extensional deformation at middle to lower crustal levels might have occurred in the early Mesozoic. The late Mesozoic granitoids have a U–Pb zircon age of 135±2 Ma, and are made up of large elliptical granitic plutons. They are high-K calc-alkaline, and were forcefully emplaced in the dome extensional setting. Both the early and late Mesozoic granitoids have εNd ( t) values of −2.3 to +5, in strong contrast with the negative εNd ( t) values (−11) of the Precambrian host rocks. This suggests that juvenile mantle-derived components were involved in the formation of the granitoids. The similar situation is omnipresent in Central Asia. This study demonstrates that tectonic extension, magmatism and crustal growth are closely related, and that post-collisional and intraplate magmatism was probably a significant process for continental growth in the Phanerozoic.