Granitic Magma Research Articles

Meso-Neoproterozoic tectonic-thermal events in the Qaidam Block, NW China and their geological significance: Constraints from drill cores geochronology and geochemistry studies

As a micro-continent lying at the junction of the North China, Yangtze, and Tarim Cratons in northwest China, the composition and tectonic-thermal history of the Qaidam Block not only are crucial for determining its tectonic attribute and relationships with surrounding cratons, but also can provide key constraints on convergence, fragmentation, and paleogeographic reconstruction of Columbia and Rodinia. In this study, systematic petrology, geochemistry, and zircon U–Pb–Hf isotope analyses were conducted on newly discovered Meso-Neoproterozoic granitic rocks from drill cores in the Qaidam basin and three stages granitic magmatism at ca. 1420 Ma, ca. 900 Ma and 780–750 Ma are yielded. The ca. 1420 Ma granitic rocks exhibit characteristics of highly fractionated I-type granites, with high Yb but low Sr contents, low Sr/Y and La/Yb ratios, high zircon saturation temperatures (774–831 ℃), and positive εHf(t) values (–0.04 to +11.35) with TDM2 values of 2178–1468 Ma, suggesting that they were mainly derived from the ancient crust with mantle magma input under an extensional setting. The ca. 900 Ma granitic rocks have high A/CNK values (1.01–1.21) and variable zircon εHf(t) values (–1.93 to + 6.58) with TDM2 ages between 1402 and 1910 Ma, indicating they are S-type granites formed by partial melting of sedimentary rocks in thickened crust. The ca. 780–750 Ma granites have high Zr + Nb + Ce + Y contents, 10000* Ga/Al ratios, and crystallization temperatures (mean = 808 ℃), belonging to the A1-type granite formed in a continental rift setting.Combined with the previous researches, the Meso-Neoproterozoic tectonic-thermal events in the Qaidam Block can be divided into three stages, 1.8–1.1 Ga, 1.0–0.9 Ga and 850–750 Ma, corresponding to the fragmentation of Columbia, and the assembly and breakup of Rodinia, respectively. Comparing the Qaidam Block with the surrounding blocks and the major cratons in Columbia and Rodinia, it is considered that the Qaidam Block was splited from the Tarim Craton and they may have occupied an interior position in Columbia but a peripheral position in Rodinia, connecting to the India and East Antarctica.

Apatite geochemical composition of Mesozoic granitoids in the eastern Jiangnan Orogen, S. China: insights into petrogenesis and intrinsic magmatic variables

ABSTRACT The geochemical compositions of apatite are commonly used to provide reliable constraints on the intrinsic magmatic variables of the parental magma. There is a widespread distribution of Mesozoic granitic rocks in the eastern Jiangnan Orogen (EJNO), which include I-type and A-type granitoids. This study aims to investigate the geochemical composition of apatite in 11 representative I-type and A-type granitic intrusions from the EJNO to understand their petrogenesis, intrinsic magmatic variables, and polymetallic mineralization potential. The results show that apatites in these granitoids were characterized by oscillatory zonation and homogeneous texture, and exhibited high F, and low Cl contents, as well as high REE, Y, and Th contents, indicating magmatic origin. These apatites were divided into two groups depending on their geochemical characteristics and original rock types. In Group I apatites (in the I-type granitoids), the absence of an abrupt change in major and trace element concentrations from the core to the rim of the apatite crystals, combined with their low levels of MgO, Sr, and HREY (HREE+Y), serves as evidence to classify the I-type granitoids as low Sr-Y adakitic granitoids with a low Mg#, which can be attributed to the partial melting of the thickened lower crust. In Group A apatites (in the A-type granites), the normal increase in incompatible elements from the core to the rim, as well as the presence of a flat REE pattern with pronounced Eu anomalies, can be attributed to crystal fractionation of plagioclase, allanite, and zircon. Furthermore, Group I apatites have higher SO3, Cl, and molar OH/F and Cl/F ratios compared to Group A apatites. Quantitative calculation by apatite-melt partitioning and modelling suggests that the I-type granitic magmas were more volatile-rich and more oxidized than A-type granitic magmas. Taken together, based on the relationship between the intrinsic magmatic variables and the behaviour of ore-forming elements, our study demonstrates that early I-type granitoids of the EJNO have a strong W-Mo-Cu polymetallic mineralization potential, while late A-type granites may possess rare metal mineralization potential.

Garnet geochemistry reveals late-stage oxidation of tin-bearing fractionated granite

In hydrothermal tin (Sn) systems, it remains unclear whether cassiterite precipitates from reduced or oxidized fluids. To resolve this issue, the geochemistry of magmatic garnet and cassiterite separated from fractionated muscovite-garnet granite in the Paleocene Bawapin SnW deposit was systematically investigated. CaO contents in Mn-rich garnet (spessartine) decrease from core to rim in single crystals and are negatively correlated with MnO/(MnO + FeO) ratios. These features suggest that garnet CaO content may be a good differentiation index for granitic magma evolution. Moreover, the Sn content in Mn-rich garnet increases with increasing Ca content and then decreases sharply at Ca contents of approximately 4300 ppm. Combined with evidence of Ta-rich magmatic cassiterite, the decreasing Sn content likely reflects the crystallization of magmatic cassiterite from the more evolved Sn-rich melts under oxidized conditions (ƒO2 > ΔFMQ +1.5), in contrast to the reduced characteristics of the less-fractionated biotite monzogranite (ƒO2 = ΔFMQ - 0.5). Late-stage oxidation might be attributable to fluid exsolution in the water-rich and Fe-poor granitic melts. This further indicates that hydrothermal cassiterite could precipitate in exsolved Sn4+-bearing fluids without Sn oxidation. This conclusion may provide a new perspective to our understanding of granite-related hydrothermal Sn systems worldwide.

Zircon and cassiterite U-Pb geochronology and petrochemical characteristics of early Tertiary tin mineralization at Mayo Darlé, Cameroon Volcanic Line

Tin mineralization at Mayo-Darlé in the Cameroon Volcanic Line is associated with highly evolved anorogenic ferroan granite magmatism with a pervasive hydrothermal overprint. Mineralization occurs as cassiterite-quartz-muscovite stockwork and disseminated in quartz-mica and quartz-topaz greisen in low-Ca alkali feldspar granite with a composition near the 1 kbar haplogranitic thermal minimum. The trace element composition of zircon indicates elevated temperature (880 ± 55 °C) and very low oxidation state below the quartz-fayalite-magnetite buffer. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) identifies a partly disturbed U-Pb system for igneous zircon (U and Th contents >1000 ppm) but defines Tera-Wasserburg concordia ages and common-lead-corrected weighted 206Pb/238U ages of about 54 Ma, similar to a previous 87Rb/86Sr vs 87Sr/86Sr regression with a date of 56.1 ± 1.7 Ma (MSWD = 58; n = 9) and an initial 87Sr/86Sr ratio of 0.7085 ± 0.0035 (2 s). Hydrothermal cassiterite gives a pooled LA-ICPMS Tera-Wasserburg concordia age of 56.7 ± 0.6 Ma on two samples (each about 20 points, MSWD = 0.54 and 1.3). These new age data define a period of early Cenozoic intraplate calc-alkalic felsic magmatism as a precursor to abundant Oligocene to Recent alkali basalt volcanism along the Cameroon Volcanic Line. Geochemical and Sr–Nd–Hf isotopic data suggest that the granitic rocks from Mayo Darlé were largely derived by partial melting of Mesoproterozoic basement and modified by strong differentiation, all likely powered by heat (and possibly fluids) from the mantle. The Tertiary age of the rare-metal magmatism sets this system apart from the widespread Late Neoproterozoic to Early Paleozoic rare-metal pegmatites and granites in the Pan-African collisional belts of Africa, and also from the anorogenic Mesozoic ring complexes in Central Nigeria.

Indosinian W–Sn mineralization in the Dupangling area, Western Nanling: Cassiterite U–Pb dating and trace element data for the Maoershi Sn polymetallic deposit

Nanling is located in central South China and contains the most important area of W–Sn polymetallic deposits worldwide. However, a lack of geochronological data hinders our understanding of the timing and mechanisms of W–Sn mineralization in the Dupangling area of western Nanling. The Maoershi Sn polymetallic deposit is located in the western body of Dupangling complex pluton, and is a significant hydrothermal vein deposit. Cassiterite U–Pb dating shows that the Maoershi Sn mineralization occurred during the Late Triassic (206.2 ± 2.6 Ma). This age is different from the age of granite in the western Dupangling pluton and similar to the age of the eastern Dupangling pluton. The cassiterite is enriched in Sc (4.5105–18.4049 ppm), V (37.2267–88.9671 ppm), Nb (62.0104–194.1846 ppm), Ta (11.1965–85.6881 ppm), Hf (22.0511–30.7650 ppm), U (2.8870–17.9187 ppm), Th (0.0005–0.0908 ppm), Ti (3873–6170 ppm), and other high-field-strength elements. Based on Nb/Ta and Y/Ho ratios, and the W–Fe discriminant diagram, Sn and the other mineralizing materials were mainly derived from hidden Indosinian granitic rocks. Tungsten–Sn mineralization in the Dupangling pluton exhibits a clear spatial–temporal relationship with Indosinian granitic magmatism, and occurred in an extensional setting after the continent–continent collision that marked the late Indosinian Orogeny.

Magmatic evolution of the La Huerta Plutonic Complex, Jalisco: A 80–70 Ma record of arc magmatism along the Mexican Cordillera

The La Huerta Plutonic Complex (LHPC) forms part of the Cretaceous Mexican Cordillera, located between the well-documented ~80 Ma Puerto Vallarta Batholith (PVB) and the ~65 Ma Manzanillo Plutonic Complex (MPC). The LHPC shares lithological and geochemical features with the aforementioned batholiths and is dominated by voluminous granitoids and hybrid intrusions ranging from gabbro to granitic compositions. Scarce cummulitic gabbroic plutons are also present. Detailed petrographic, geochemical, microchemical, and geochronological results provide evidence for three magmatic stages: (1) a gabbroic magmatism at >84 Ma (observed from field relations), (2) ~83–80 Ma granitic magmatism (U-Pb in zircon), and (3) a ~75–70 Ma gabbroic and granitic magmatism (U-Pb in zircon). Thermobarometric determinations (3.0–2.0 kbar and <900 °C) and Sr-Nd isotopic signatures in all lithologies (εNdi from +4.2 to +6.2 and 87Sr/86Sri around 0.7035) suggest a shallow magmatic environment with low and heterogeneous crustal assimilation. These features hold considerable differences with the northern PVB and are more comparable to the MPC. The LHPC is interpreted as the south easternmost part of the PVB and as a transitional zone between the PVB and the MPC.

Tracing tungsten-tin mineralization processes with tourmaline geochemistry in the Wangxianling-Hehuaping district, Nanling Range (South China)

The mechanisms controlling the enrichment and separate precipitation of tungsten and tin ores are obscure. To unravel the physicochemical changes in the mineralization system during the magmatic-hydrothermal transition, we investigate the petrography, geochemistry, and boron isotopes of tourmaline in the Wangxianling-Hehuaping district (Nanling Range, South China). Four types of tourmalines were identified: Magmatic (Tur-WG) and hydrothermal (Tur-WV) tourmaline in the Triassic W-mineralized tourmaline-two-mica granite (ca. 220 Ma); Magmatic (Tur-SnG) and hydrothermal (Tur-SnV) tourmaline in the Jurassic Sn-mineralized biotite granite (ca. 155 Ma). Tur-WV and Tur-SnV have lower Fe3+/(Fe2+ + Fe3+) ratios than those of Tur-WG and Tur-SnG, suggesting that W-Sn mineralization occurred in a relatively reducing environment. In addition, the δ11B values of all four types of tourmalines are similar, suggesting that the ore-forming fluids were primarily exsolved from the granitic magma. Significant chemical variations (e.g., Mg, Fe, Sc, V, Ni, and REEs) between Tur-SnG and Tur-SnV may have been resulted from fractionation and intense ore fluid-wall rock reactions. In contrast, Tur-WG has similar chemical compositions to Tur-WV, suggesting that the Triassic W mineralization may have undergone a magmatic-hydrothermal process with little ore fluid-wall reaction. Tur-SnV has exceptionally high F content, which could enhance the Sn solubility and enrichment. This explains the low Sn content of granitic magmas with large-scale Jurassic tin mineralization. Considering that W has a large melt-fluid partition coefficient, we conclude that in the Triassic, W is enriched in the exsolved fluid from the granitic magma and precipitated with temperature drop. This may have caused the decrease in W content in the protolith and limited the Jurassic W mineralization. Subsequently, the mantle-derived F addition along the Chenzhou-Linwu fault in the Jurassic had led to Sn enrichment in the fluids, and mineralization is triggered by temperature drop and fluid-rock reactions. Eventually, the extensive Triassic W mineralization and Jurassic Sn mineralization exhibit the separation of tungsten-tin mineralization. The separated tungsten-tin mineralization model based on different volatile components could also be applicable to other tungsten-tin metallogenic belts.

Indosinian W-Sn mineralization event in the Xikeng deposit, southern Jiangxi Province, Nanling Range: Evidence from U-Pb geochronology and Hf isotopes

The Chongyi–Shangyou–Dayu ore-concentrated district represents one of the most important wolframite production bases in China, and most of the W-Sn deposits formed in the early Yanshanian period. The Xikeng quartz vein-type W-Sn deposit is located spatially not far from the Triassic Keshuling granitic pluton. The deposit contains 43 ore-bearing quartz veins, in which the ore minerals are mainly cassiterite and wolframite. These ore veins are concentrated in the Sinian metasandstone and sandy slate of the Laohutang Formation and extend down to the top of the concealed granite. The concealed intrusion is composed of medium- to fine-grained muscovite granites, which relate to the Indosinian Keshuling granite, according to geophysical data. Zircon grains from the concealed Xikeng granitic intrusion have a concordant U-Pb age of 232.1 ± 1.1 Ma (MSWD = 0.9). The zircon εHf(t) values range from −11.0 to −7.9, indicating primary reworking of the ancient crustal materials. Wolframite and cassiterite grains yield Tera-Wasserburg concordia intercept ages of 228.4 ± 0.9 Ma (MSWD = 1.2) and 227.8 ± 1.6 Ma (MSWD = 0.3) for the Xikeng deposit, respectively. These data demonstrate that the Indosinian W-Sn mineralization events were genetically related to granitic magma activities that share similar magmatic sources with the Yanshanian W-Sn mineralization-associated granitic intrusions. Combined with previous robust granitic and metallogenic ages, this paper identifies a new Indosinian W-Sn mineralization event in southern Jiangxi Province, Nanling Range.

A Long-Lived Accretionary Process during the Amalgamation of the North China Craton: Insights from Neoarchean–Paleoproterozoic Polyphase Magmatism in the Lüliang Complex

Abstract There has been a long debate regarding the timing of the final amalgamation of the North China Craton, which is considered to have occurred either during the Neoarchean or Paleoproterozoic era. One major point of contention is whether there existed a long-lived subduction lasting through the Neoarchean to Paleoproterozoic. The Lüliang Complex contains multiphases of magmatism and thus represents the most viable region to address this controversy. In this study, we carried geochronological and geochemical analysis on the representative granitoids. Secondary ion mass spectrometry U–Pb dating revealed four distinct granitoid groups emplaced at 2531 ± 4, 2189–2173, 2027 ± 25, and 1852 ± 41 Ma, respectively. Notably, the 2531 Ma granitic gneiss was identified for the first time in this region. Based on the geochemical characteristics, the granitoids can be divided into two types. The 2531 and 2027 Ma groups display I-type features, while the 2189–2173 and 1852 Ma groups exhibit A-type geochemical affinities. Both I-type groups exhibit enrichment in Rb, depletion in Nb, Ta, and Ti, moderate fractionated REE patterns, substantial negative Eu anomalies, low Sr/Y ratios, and positive εHf(t) (+3.51 to +5.53 and +5.59 to +7.32, respectively), indicating that they were generated from partial melting of the juvenile mafic crust. In contrast, the 2189–2173 Ma granitoids belong to A2-type and were most likely generated by the partial melting of felsic rocks in the back-arc region, while the 1852 Ma granitoids belong to A1-type and were most possibly the result of partial melting of mafic-intermediate rocks during the post-collisional stage. Based on the records of A-type granitic magmatism and the ~1950 Ma peak metamorphism throughout the Trans-North China Orogen, we propose that a long-lived subduction process (2531–1950 Ma) can mostly explain the existing geological phenomena. It is likely that the subduction between the Eastern and Western Blocks should have commenced at ~2531 Ma, followed by a long-lived subduction. The two blocks ultimately collided with each other to form the North China Craton at ~1950 Ma, which triggered post-collisional exhumation and partial melting at ~1852 Ma.

Fluid evolution and mineralizing process of the Bawang Fe-Zn-Sn deposit, Danchi Fold-and-Thrust belt, South China

The Bawang deposit, a newly discovered Fe-Zn-Sn deposit occurred in the paleokarst in the Youjiang Basin, South China, offers an excellent opportunity to understand the ore-forming process and genesis of this unique tin mineralization, thus enriching the tin mineralization theories. Mineralogy, X-ray photoelectron spectroscopy (XPS), and laser ablation-inductively coupled plasma-mass (LA-ICP-MS) analysis were performed on sphalerite to investigate the fluid evolution and mineralizing process of the Bawang deposit. The formation of the deposit involved hydrothermal-cassiterite-sulfides and oxidation periods. The hydrothermal-cassiterite-sulfides period is dominated by the mineralization of Zn- (stage 1), Sn- (stage 2), and Sb- (stage 3) in order. Three types of sphalerite were identified in these hydrothermal stages. Mineralogical studies and spectrum data show that the massive sphalerite in stage 1 (Sp1) is euhedral coarse-grained and characterized by high Fe contents (9.67–15.69 wt%), with obvious pyrrhotite blebs, pyrite laths, stannite and/or chalcopyrite solid solutions. The sphalerite with 5.56–11.31 wt% Fe contents in stage 2 (Sp2) occurs as fine-grained, euhedral to subhedral crystals (15–50 μm) and coexists with cassiterite, arsenopyrite, and quartz. The sphalerite in stage 3 (Sp3) is characterized by low Fe content (0.59–2.99 wt%) and is generally micro-fine-grained (10–30 μm) associated with stibnite, sulfosalts, and carbonates. LA-ICP-MS analyses of sphalerite suggest that Sp1 and Sp2 have similar characteristics and are enriched in Fe, Cu, Sn, Ga, and Cd, whereas Sp3 is enriched in Sb, Pb, Ag, Bi, and Tl. The principal component analysis (PCA), boxplots, and bivariate plots of trace elements from sphalerite, combined with previous Raman spectroscopy data for fluid inclusions and H-O-Cd isotopic compositions, indicate two types of ore-forming fluids were involved in the mineralization of the Bawang deposit. The early Fe-Zn-Sn-Cu-In-rich fluids originated from granitic magma and underwent Zn- and Sn-dominated mineralization in order in a slowly cooling closed system. The later hydrothermal fluids with the addition of oil field brine were enriched in Sb, Pb, Ag, and Bi elements in the Sb-sulfosalts-carbonates stage in an open system with a drop in temperature. The mineralization process of the Bawang deposit can be concluded as follows: The early ore-forming fluids derived from an inferred concealed intrusion infilled into the paleokarst (below 350 m of the altitude) and caused the massive euhedral ferroan sphalerite (stage 1) to precipitate. The deposition of sphalerite decreased sulfur fugacity (fS2) in a slowly cooling closed system, and increased relative oxygen fugacity (fO2) which promoted cassiterite to precipitate in stage 2. The foreign hydrothermal fluids lowered the temperatures of residual ore-forming fluids due to the addition of oil field brine. Then the Pb-Sb sulfides and Pb-Sb-Ag-Bi-bearing sulfosalts (stage 3) crystallized at shallow depths (350 to 500 m of the altitude).

Origin of Silurian granite in the Baiganhu field, Eastern Kulun Terrane, NW China: Implications for the tectonic setting of Sn-W mineralization

The Baiganhu area in the Eastern Kunlun Terrane on the northern margin of the Tibetan Plateau contains world-class Sn-W deposits in close association with monzogranite. However, the origin of granite and the tectonic setting for the Sn-W mineralization have not been well constrained. Here we present the petrological and geochemical data of the granite (431 Ma) associated with the Sn-W mineralization to evaluate the geological-tectonic setting for the mineralization. The monzogranite has high SiO2 contents, ranging from 65.8 to 73.5 wt%, and shows a geochemical affinity with A2-type granites. Relatively high zircon saturation temperatures, ranging between 750 °C and 921 °C, suggest that the parental magmas were hot. The whole-rock εNd (t = 431 Ma) values range from –2.7 to –3.1 with TDM ages between 1810 and 1040 Ma, and zircon εHf (t = 431 Ma) values range from + 0.7 to + 4.1 with TDM ages between 1040 and 900 Ma. The data suggest that the magmas had significant contributions of old rocks. The granitic rocks intruded into quartz-muscovite schist of the Proterozoic Xiaomiao Complex, which underlies the vast area. Zircon grains in the schist are magmatic in origin based on sharp oscillatory zoning and high Th/U ratios (>0.2). The 207Pb-206Pb zircon ages (n = 25) of the schist range from 1898 ± 2 to 1700 ± 6 Ma, suggesting that the zircon grains originate from a Paleoproterozoic magmatic belt. Such ancient rocks, either as lower crustal component or subcontinental lithospheric mantle, contributed ∼ 30 % to the parental magmas. We conclude that post-collisional extension within the Eastern Kunlun Terrane was accompanied by upwelling and adiabatic melting of the asthenospheric mantle which induced partial melting of subcontinental lithospheric mantle and lower crustal rocks and formed granitic magmas. Aqueous fluids separated from the granitic magma which preferentially incorporate W and Sn contributed to the mineralization in and around the granites.

Geochemistry and Zircon U–Pb Geochronology of the Wugongshan Granites in the Northwestern Jiangxi Area, China: Implications for the Paleozoic Tectonic Development of South China

The properties of the Caledonian orogeny along the transition belt of the Yangtze and Cathaysia blocks have received much attention in recent years. The widespread Early Paleozoic granites provide critical geological clues for unraveling the tectonic evolution and geodynamic processes of the South China Continent (SCC). Here we present new zircon U–Pb chronology, whole-rock major and trace elements, in situ Hf isotopes for Paleozoic granites, i.e., the Wugongshan granites in the northwest Jiangxi province, and aim to explore the magmatism and properties of the Caledonian orogeny involved in their formation. Our new data show that the Wugongshan granites were emplaced during the Early Silurian Period (442–438 Ma). The Paleozoic Wugongshan granites belong to S-type muscovite-bearing peraluminous granites (MPG) and show a single origin. The Wugongshan granites exhibit negative εHf(t) values (−11.56 to −6.19) and TDM2 model ages of 2148–1809 Ma, indicating their derivation from an ancient crustal source, through partial melting of ancient crustal material. The Wugongshan granitic magmatism is probably being generated in an extensional environment related to an intracontinental orogeny setting. It is inferred that the Paleozoic tectonic–magmatic event in the Wugongshan area was associated with the oceanic–continental convergence of the Paleo-Tethys Ocean. The Wugongshan granites highlight the intracontinental magmatism in the Early Paleozoic orogeny in the SCC.

Ocean–Continent Conversion in Beishan Orogenic Belt: Evidence from Geochemical and Zircon U-Pb-Hf Isotopic Data of Luotuoquan A-Type Granite

Devonian magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt (CAOB). However, little is known regarding the petrogenesis and geodynamic setting of the widely distributed Devonian granitoids in the eastern Southern Beishan Orogenic Belt (SBOB). Early-Devonian granitic magmatism has been recognized from the Luotuoquan area, and the granites were emplaced between 404.9 Ma and 399.4 Ma according to LA-ICPMS zircon U–Pb dating. Geochemically, the granites exhibit high SiO2 and Al2O3 contents and are enriched in light rare earth elements as well as Rb, Th, Nd, Zr, and Hf, while being depleted in heavy rare earth elements and Ba, U, Sr, and Ti, with distinct rare earth element fractionation and pronounced negative Eu anomalies. According to the comprehensive analysis, they closely resemble the features typically associated with A-type granites. The zircons εHf(t) values are within the range of +0.90–+5.19 (averaged 3.23) for the monzogranite and syenogranite, whereas their TDM2 values fall between 1.05 and 1.34 Ga, suggesting that the magma source of the monzogranite–syenogranite originated from the partial melting of the Mesoproterozoic crust dominated by metagreywackes. Furthermore, the monzogranite and syenogranite exhibit high temperatures (average 782 °C), thin crustal thickness (average 30 km), and A-type characteristics, suggesting their formation in post-collision extensional settings. We propose the closure of the Beishan Ocean occurred before the early Devonian, followed by a transition in the Southern Beishan Orogenic Belt from a compressional to an extensional setting.

Mid-Mesoproterozoic (ca. 1.37 Ga) anorogenic magmatism in the Dabie orogen, northern Yangtze Craton: Response to the breakup of Columbia

It is evident that the Yangtze Craton was involved in the formation and breakup of the Columbia supercontinent. However, due to the scarcity of Mesoproterozoic geological records and reliable paleomagnetic data, little is known about the timing, paleogeographic position, and geological processes of the Yangtze Craton. We conducted detailed geological mapping, petrographic, geochemical, and in situ zircon U-Pb and Lu-Hf isotopic investigations on newly recognized Mesoproterozoic quartz syenite and monzogranite in the Dabie orogen, northern Yangtze Craton. The results show that the quartz syenite and the monzogranite were emplaced at 1369 ± 12 Ma and 1372 ± 5 Ma, respectively. Both rocks are high in total alkali (K2O + Na2O) content and FeOt/(FeOt + MgO), with elevated diagnostic 10,000*Ga/Al ratios and Zr + Nb + Ce + Y concentrations, and enrichment in light rare earth elements. They are also depleted in heavy rare earth elements with significant negative Eu anomalies but remarkably low Sr, Cr, and Ni contents. These compositions define affinity to A1-type granite. In addition, the quartz syenite displays variable zircon Hf and homogeneous whole-rock Nd isotopic compositions with positive εHf(t) values of +0.7 to +5.7 (average +2.4) and εNd(t) values of −0.1 to +2.5 (average +1.0). In contrast, the monzogranite has homogeneous zircon Hf and whole-rock Nd isotopic compositions with negative εHf(t) values of −5.7 to −2.6 (average −4.8) and εNd(t) values of −3.5 to −1.5 (average −2.2). We propose that the quartz syenite was likely generated by the partial melting of juvenile, crust-derived melt with involvement of minor mantle-derived material, while the monzogranite was likely derived from the partial melting of ancient crust in an extensional tectonic regime (e.g., continental rift). Based on the newly recognized ca. 1.37 Ga granitic magmatism and previously reported magmatic events, we argue that the mid-Mesoproterozoic (ca. 1.37 Ga) magmatism in the Yangtze Craton occurred in response to the breakup of Columbia, and represents the separation of the Yangtze Craton from Columbia. Furthermore, according to comparable magmatic and sedimentary events, we propose that the Yangtze Craton, along with central Hainan Island, may have been linked to northwestern Laurentia, southwestern Siberia, and northeastern Australia during 1.6−1.4 Ga.

An early Paleozoic accumulation-foundering cycle of ultramafic cumulates in the Harlik arc and its implications for continental crustal growth in the Altaids

Lower crustal ultramafic cumulates that are normally denser than the ambient mantle peridotites are prone to founder back into the convecting mantle, prompting the formation of continental Moho and andesitic crust at subduction zones. However, foundering events of ultramafic cumulates have not been widely reported in island arcs, including the Altaids, one of the largest accretionary orogens. The Altaids involved prominent continental crustal growth by the development of an archipelago in the Phanerozoic. But the scarcity of foundering events of ultramafic cumulates hinders a better understanding of the formation mechanism of andesitic crust in the Altaids. In this study, we report two dioritic plutons in the Harlik arc, southern Altaids, trying to identify the accumulation-foundering cycles of dense ultramafic cumulates. LA-ICP-MS dating revealed that the Miaoergou and Banfanggou plutons in the Harlik arc were intruded at ca. 445 ± 6 Ma and 423 ± 4 Ma, respectively. The homogeneous Miaoergou pluton is mainly composed of quartz diorites, they have a high- to medium-K calc-alkaline composition, and show enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta) and heavy rare earth elements (HREE). They also have juvenile isotopic signatures (εNd(t) = +3.3 − +3.7, initial 87Sr/86Sr = 0.70399–0.70452), which together suggest that they were derived from fractional crystallization of the coeval hydrous basaltic magmas in an arc setting. The heterogenous Banfanggou pluton comprises a spectrum of lithologies from hornblende gabbro to diorite. The hornblende gabbros and diorites have a high- to medium-K calc-alkaline composition, and show enrichments in LREE and LILE, but depletions in HREE and HFSE. They all have juvenile isotopic compositions with εNd(t) ranging from +3.5 to +4.2, and (87Sr/86Sr)i from 0.70384 to 0.7047, respectively, indicating that their parental magmas were intruded in a subduction-related setting, and underwent fractional crystallization of clinopyroxene, plagioclase, amphibole and quartz. Both pulses of hydrous basaltic magmatism involved open-system conditions, with the development of mafic microgranular enclaves (MMEs) in the diorites and their mingling. In a synthesis of the published data, we found that the Harlik arc was continuously affected by subduction in the early Paleozoic, through extensive arc magmatism from ca. 452 to 440 Ma, the Harlik arc matured with the accumulation of thick ultramafic cumulates in its lower crust. The foundering of these ultramafic cumulates occurred later, which led to strong extension and related A-type granitic magmatism at ca. 436 Ma. This accumulation-foundering cycle of ultramafic cumulates facilitated the formation of andesitic composition and continental Moho in the Harlik arc, and contributed to the significant continental crustal growth in the Altaids.

Origins and evolution of two types of Late Triassic granitic magmas in the Caolong-Xiangkariwa area of central-eastern Songpan-Ganze terrane, northern Tibet: Implications for pegmatite lithium mineralization

Pegmatite-type lithium (Li) deposits are an important source of the low-carbon energy metal, which is generally considered to be formed by the high degrees of differentiation of strongly peraluminous granitic magma. However, the question of whether the parental rocks of these peraluminous magmas are igneous or sedimentary has been widely debated. Recent studies have identified a world-class pegmatite-type Li deposit belt (up to 2800 km long) closely associated with the Late Triassic granitoids and (meta)sedimentary rocks along the West Kunlun and Hoh Xil-Songpan-Ganze terranes in northern Tibet. This study presents a comprehensive petrological, geochronological, and geochemical study on the two types of Late Triassic granitoids in the Caolong-Xiangkariwa area of the Yushu region of central-eastern Hoh Xil-Songpan-Ganze terrane in northern Tibet: type A includes the Tongtianhe-Zhenqin-Zhaduo-Zhaya-Xiangkariwa (TZX) diorites and granodiorites (218−212 Ma), and type B includes the Caolong two-mica and muscovite granites (213−205 Ma), as well as ore-barren, beryl-bearing, and spodumene-bearing pegmatite dikes (209−196 Ma). The TZX diorites and granodiorites contain variable amounts of amphibolite and biotite. They are metaluminous to slightly peraluminous with variable SiO2 (54.4−71.3 wt%), MgO (0.72−7.26 wt%) contents, and Mg# values (40−70). Some samples with low SiO2 (54.4−58.5 wt%) contents have geochemical features similar to high-Mg andesites: e.g., high MgO contents (5.24−7.26 wt%) and Mg# values (61−70). The TZX diorites and granodiorites exhibit less enriched (86Sr/87Sr)i (0.7080−0.7118) and εNd(t) (−4.8 to −8.0). By contrast, the Caolong two-mica and muscovite granites are characterized by the occurrence of abundant muscovite (plus tourmaline and garnet) and are strongly peraluminous. The Caolong granites and pegmatites are geochemically characterized by high SiO2 contents (68.8−79.8 wt%) and low MgO contents (0.01−0.10 wt%) and Mg# values (4−23). They have εNd(t) values (−8.8 to −11.4; granites: −8.8 to −10.8; pegmatites: −9.2 to −11.4) that are more enriched than the TZX diorites and granodiorites but similar to those of Songpan-Ganze (meta)sedimentary rocks (−7.4 to −12.9), and the Caolong two-mica granites have high zircon δ18O values (11.6−12.1). In addition, decreasing K/Rb ratios correspond to increasing Cs contents in K-feldspar and muscovite from the Caolong granites and pegmatites. Taking into account the Late Triassic granitoids and (meta)sedimentary rocks in the Hoh Xil-Songpan-Ganze terrane, we suggest that the TZX diorites and granodiorites were most probably formed by the partial melting of metasomatized lithospheric mantle that subsequently underwent extensive fractional crystallization. Conversely, the Caolong two-mica and muscovite granites were likely generated purely by the partial melting of (meta)sedimentary rocks rather than via the evolution of dioritic-granodioritic magmas. In summary, there were two kinds of granitic magmas with different sources in the Caolong-Xiangkariwa area. Finally, the Caolong pegmatites were most likely formed by the extreme differentiation of two-mica granitic magmas rather than the dioritic-granodioritic magmas. Therefore, the evolution of magmas derived from (meta)sedimentary rocks were most likely to have formed the Li-rich pegmatites. Moreover, these (meta)sedimentary rocks representing the ultimate Li source must have undergone strong chemical weathering, resulting in significant Li enrichment.

Boron isotopes in tourmaline from drill core of the Jiajika granitic pegmatite type lithium deposit: Insights for granitic magma evolution and lithium enrichment

The Jiajika pegmatite-type Li deposit located in the southeastern Songpan-Ganze terrane of the eastern Tibetan Plateau is one of the largest hard-rock Li deposit in China, and its ore-genetic mechanism is still controversial. To understand the Li concentration of potentially economic levels in the Jiajika pegmatite-type Li deposit, the association between Li enrichment and granitic magma evolution is investigated using B isotope in tourmaline grains along the entire 3211-m-depth of the JSD-1 drill core in this work. Tourmalines hosted in granite, pegmatite, barrovian-type metamorphic rock and calc-magnesium-silicate metamorphic rock are being plotted in the fields of Li-poor granitoids and associated pegmatites and aplites on the Al-Fe-Mg and Ca-Fe-Mg ternary diagrams. These characteristics, along with their high Fe/Mg ratios and high Al cation numbers in Y position, are indicative of a magmatic origin. The B isotope (δ11B) of tourmalines in granite and pegmatite in Jiajika granitic pegmatite type Li deposits vary from −9.49 to −7.06‰, in line with the range observed in 90 % of worldwide granites and pegmatites. In comparison of the measured data of δ11B vs. Li to the modeled curves indicates that the differentiation process of granitic magma follows an equilibrium crystallization model better than a fractional crystallization model. The compiled evidence proves that magma differentiation accompanied by fluid exsolution facilitates the enrichment of Li during granitic magmatic evolution. The formation of the domal structure of granitic sheets due to the decompressing effect of magma ascent favors massive fluid exsolution at the late-stage granitic magma, which contributes to the deposition of spodumene dominated ore body at the shallower depth of 5–150 m.

Breaking up the temporal link between granitic magmatism and iron oxide-copper–gold (IOCG) deposits in the Carajás Mineral Province, NW Brazil

Breaking up the temporal link between granitic magmatism and iron oxide-copper–gold (IOCG) deposits in the Carajás Mineral Province, NW Brazil

The late Early-Paleozoic granitic magmatism in Northwestern Fujian, China: constraints on intraplate orogeny in the South China block

The late Early-Paleozoic granitic magmatism in Northwestern Fujian, China: constraints on intraplate orogeny in the South China block

Early Cretaceous magmatic-hydrothermal processes for the lode Yingdongpo gold and Poshan silver deposits in the Tongbai Orogen, central China

Numerous lode gold and silver deposits occurred in orogenic belts in China, although some were related to intrusions within anorogenic settings. Genesis of lode gold and silver deposits in the Tongbai-Dabie orogen remains equivocal. In this study, Rb–Sr dating, electron microprobe and LA-ICP-MS element analyses of sulfides, fluid inclusion microthermometry and H–O isotopic analyses were carried out to decipher the formation and fluids evolutions producing the super-large Yingdongpo gold and giant Poshan silver deposits. Sphalerite Rb–Sr dating yields isochron ages of 133.3 ± 3.0 Ma and 136.1 ± 1.8 Ma for the Yingdongpo and Poshan deposits, respectively, suggesting that both deposits formed coevally with Early Cretaceous granitic magmatism. H–O isotopic data indicate that the ore-forming fluids of both deposits were primarily of magmatic origin with meteoric water inputting. Their initial ore-forming fluids were CO2-rich, with high temperatures and intermediate salinities. At the Yingdongpo gold deposit, native gold and electrum coexist with polysulfides; invisible Au mostly occurs as nanoparticle inclusions in sulfides and is associated with As. At the Poshan silver deposit, Ag gradually increases in early to late generations of sphalerite, and is positively correlated with Pb. Silver minerals likely formed via exsolution from galena due to progressively decreasing temperatures. There are discrete processes of ore-forming fluids, with different mechanisms responsible for gold and silver mineralization. Au mineralization is related to an abrupt change of the physicochemical properties in fluids immiscibility at 190° to 265 °C; whereas Ag mineralization is favored by progressive deposition of sulfides in a slowly cooling hydrothermal system with temperatures from 317° to 88 °C.