Eclogites provide important constraints on the processes of plate subduction, collision, and the overall tectonic evolution of orogens. The Gubaoquan eclogite is the only one identified in the Beishan Orogenic Belt, which constitutes the southernmost part of the Central Asian Orogenic Belt. U-Pb dating of the eclogite indicates a Neoproterozoic metamorphic age of 887 +/- 7 Ma and an Ordovician age of 461 +/- 15 Ma for the eclogitefacies metamorphism. Multi-proxy (zircon, monazite, rutile, and apatite) U/Th-Pb geochronology and trace element geochemistry reveal that they have experienced multiple tectonothermal events in the Neoproterozoic and Paleozoic. The protolith of the Gubaoquan eclogite is of continental origin, and along with the extensive distribution of the Neoproterozoic arc-related rocks probably formed near the periphery of Rodinia. Given the continental setting of the protolith of the Gubaoquan eclogite, we suggest that eclogitefacies metamorphism at ca. 461 Ma was due to subduction under the Shuangyingshan-Huaniushan arc, which is manifested as an arc-continental collision process.

Dunhuang Block is located in the northeastern margin of the Tarim Craton. The study area extensively exposed the Precambrian rocks, mainly composed of TTG gneisses, metamorphic supracrustal rocks, and Paleoproterozoic meta-mafic and felsic intrusive rocks. The study of TTG gneisses can provide insight into understanding the formation and evolution of continental crust in the Dunhuang Block. In this contribution, detailed field investigation, zircon U-Pb geochronology, geochemistry and Hf isotopic analysis of the Dongbatu Mountains area TTG gneisses in the Dunhuang Block are carried out to ascertain the petrogenesis and tectonic setting, and then to discuss the Early Precambrian tectonic evolution of the Dunhuang Block. LA-ICP-MS zircon U-Pb data reveals that the trondhjemitic gneisses of the Shangkouzi and Yinghuxia area in the Dongbatu Mountains were formed at ca. 2.6 similar to 2.5Ga, which belong to the product of Late Neoarchean magmatisms, and later underwent regional tectonic-thermal events at similar to 2.4Ga, similar to 2.0Ga and similar to 350Ma. The Dongbatu Mountains area TTG gneisses exhibit high SiO2 (67.29% similar to 76.20), Na2O (4.94% similar to 5.83%), low MgO (0.51%similar to 1.57%), K2O (0.39%similar to 1.30%) contents, and moderate Al2O3 (14.09% similar to 15.87%) contents, high Mg-# (50.2 similar to 66.1) value as well as A/CNK values of 0.96 similar to 1.04. TTG gneisses are characterized by low rare earth element (Sigma REE = 69.6 x 10(-6)similar to 174 x 10(-6)) contents, variable (La/Yb)(N) values of 23.9 similar to 141, enrichment light REEs, weakly to significant positive Eu anomalies (Eu/Eu-* = 1.08 similar to 1.81), and enriched in large-ion lithophile elements (e.g., Rb, Ba, Th and U), but depleted in high-field-strength elements (e.g., Nb, Ta and Ti). Moreover, these rocks display high Sr (551 x 10(-6) similar to 824 x 10(-6)), low Y (3.13 x 10(-6) similar to 8.98 x 10(-6)) contents, and relatively high Sr/Y ratios of 66.8 similar to 215. Hf-in-zircon isotopes characteristics of the Dongbatu Mountains area TTG gneisses show negative to positive epsilon(Hf)(t) values (-11.7 similar to +8. 3; mostly >0) with two-stage Hf model ages (t(DM2)) of 3811 similar to 2521Ma. The above geochemical characteristics indicate that the Neoarchean TTG gneisses from the Dongbatu Mountains area in the Dunhuang Block were derived from the partial melting of juvenile basaltic crust and a residue phase dominated by garnet, amphibolite and/or rutile, which formed in subducted-related or island arc tectonic setting. This study, combined with published regional geological data, suggests that the Neoarchean TTG gneisses in the Dongbatu Mountains area of Dunhuang Block were formed in the arc-magmatic tectonic setting associated with subduction, representing an important crustal growth event, followed by two regional metamorphic events in Paleoproterozoic and Paleozoic periods.

Metasomatized sub-continental lithospheric mantle (SCLM) is increasingly proposed to control the formation of giant hydrothermal gold provinces. However, the key budgets for gold and volatile components in the SCLM under gold provinces remain poorly constrained, thus hindering definitive genetic models of gold metallogenesis. The Cenozoic hydrothermal orogenic gold deposits in the Ailaoshan gold belt in SE Tibet that are genetically related to metasomatized SCLM, and adjacent penecontemporaneous lamprophyre dikes that are suggested to have a similar source, provide a rare opportunity to resolve this source budget issue. Integrated data on siderophile elements of the lamprophyre dikes, volatile contents of their melt inclusions, and their whole-rock geochemistry are utilized to constrain the source they share with the gold deposits. The lamprophyre primary magmas are characterized by high H2O (3.6 wt%), Cl (up to similar to 4700 ppm) and S (up to similar to 3100 ppm) concentrations, with modeling suggesting that their mantle sources are also significantly enriched in volatiles (H2O > 1000 ppm, Cl > 60 ppm), overlapping with those of the most volatile-rich magmas and mantle endmembers in the earth. Excluding those dikes that were either affected by auriferous fluids or experienced sulfide separation, the dikes have variable but generally normal Au concentrations (0.10-3.33 ppb), with estimated mantle sources comprising less than 1 ppb Au. This range is lower than or comparable to that of Au contents of global mantle peridotites and the primitive upper mantle, indicating that metasomatism processes did not significantly fertilize the SCLM beneath the gold province with anomalously high Au. Consequently, it appears that high volatile contents of the metasomatized SCLM, which promoted generation of auriferous fluid, ore-metal extraction, subsequent fluid transfer and advection, had a more important, and previously underestimated role in formation of the gold deposits.

The Ailaoshan orogen in SW China records the evolution of the Ailaoshan Paleo-Tethyan ocean and the amalgamation history between the South China and Indochina blocks, an important process for the formation of Southeast Asia. However, its tectonic evolution remains ambiguous with various competing models. We have carried out an integrated geochronological–petrological–geochemical study for the granites, dacites-rhyolites, granodiorites and trachyandesites in this orogen to give new constraints on this issue. The 255–254 Ma granites and the 250–248 Ma dacites-rhyolites show similar geochemical features and are characterized by strongly peraluminous nature, continental crust-like trace element patterns and negative zircon εHf(t) values (−14.4 to −6.6), indicating they derived from partial melting of ancient crust. The 229 Ma hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.96–1.01) and belong to high-K calc-alkaline I-type granites. They show depleted whole-rock Sr-Nd and zircon Hf isotope compositions (initial 87Sr/86Sr = 0.7027 to 0.7038, εNd(t) = 4.0 to 4.1, εHf(t) = 9.3 to 11.5), suggestive of derivation from partial melting of juvenile mafic crust. The 226 Ma trachyandesites are characterized by high MgO (4.1–4.6 wt.%), high Mg# (56) and arc-type geochemical affinities with enriched isotope compositions (initial 87Sr/86Sr = 0.7108 to 0.7111, εNd(t) = −7.7 to −7.5, εHf(t) = −6.3 to −3.5). These features indicate that their parental magmas derived from partial melting of enriched lithospheric mantle metasomatized by oceanic sediment-derived melts. These new data, in conjunction with spatial-temporal-temperature variations of igneous rocks, metamorphic records and stratigraphic changes in the region, suggest that the Ailaoshan Paleo-Tethyan ocean closed at the Early Triassic (ca. 250 Ma) which was followed by the Late Triassic postcollisional slab breakoff, and the ocean experienced westward unipolar subduction during its evolution with no assumed eastward subduction.

The Sushui Complex is an important component of the Precambrian basement in the southern North China Craton (NCC), and it mainly formed in the time interval from the Neoarchean to Paleoproterozoic. Although it is confirmed that the Paleoproterozoic is a key period for the final amalgamation of the NCC, and the granulite facies metamorphism can be recognized in the Sushui Complex. However, limited studies suggest that the Sushui Complex has undergone Paleoproterozoic metamorphism. Thus, a significant controversy exists regarding whether the Sushui Complex has been involved and reworked by the final assembly of the NCC. Rutile, one of the most important titanium minerals, occurs in a variety of medium- to high-grade metamorphic rocks, which have a lower closure temperature (500-630 degrees C) than zircon (>850 degrees C), thus rutile can record a wealth of useful and additional information about subsequent magmatic and metamorphic events, which makes it a complementary mineral to zircon to reveal the complete geologicalal history. In this contribution, we carried out the LA-ICP-MS U-Pb dating on zircon and rutile grains that collected from the Sushui Complex. Zircons from two trondhjemitic gneiss samples yield crystallization ages of 2520 and 2509 Ma. Rutile grains from the samples give the metamorphic ages of 1937, 1840, and 1811 Ma, respectively. The mica schist sample records the two populations of rutile U-Pb ages of 1924 and 1832 Ma. Zircon U-Pb dating reveal that the monzogranite sample was emplaced at 2300 Ma, and rutiles in the sample yield variable ages ranging from 2079 to 1715 Ma with a main peak age of 1820 Ma. The rutile U-Pb ages of the Sushui Complex reveal two distinct stages of metamorphism. The period of 1937-1924 Ma corresponds to the timing that is close to the peak metamorphism; whereas the subsequent period of 1840-1811 Ma indicates the cooling age associated with the exhumation of the basement in the Zhongtiao Mountains. Available studies reveal that the Sushui Complex has experienced Paleoproterozoic metamorphism during the final assembly of the NCC. In addition, our study provides an excellent example of how rutile U-Pb dating is a valuable geochronological tool for revealing late tectonothermal events of the Precambrian metamorphic terranes.

Major Sn deposits are commonly linked to crust-derived and highly evolved granites, with magma generation aided by mantle heating. However, whether and how the mantle components contribute to Sn polymetallic mineralization remains unclear. In this study, in combination with a compilation of equivalent data in the region, we provide new constraints on this issue based on detailed investigations on the petrogenesis and metallogenic significance of granitoids including the causative batholith and later granodiorite porphyry dike in the giant Dachang Sn deposit from South China. The former has zircon U-Pb ages of 93-91 Ma and belongs to highly evolved S-type biotite granite, which experienced fractionation of massive feldspar. The latter shows zircon U-Pb ages of 90 Ma and displays I-type granite features. The batholith was mainly derived from the dehydration melting of biotite in the metasedimentary sources, as revealed by the relatively low whole-rock Pb contents (<30 ppm) and high Ba/Pb ratios (2.71-17.1) and initial T(ti-zr) of 790 degree celsius. Compared with the adjacent crust-derived S-type granites (-24.8 - -5.1) and I-type granites (-11.0 to -5.2), the Dachang S-type biotite granites present higher zircon epsilon Hf(t) values (-9.1 to -2.1). Furthermore, the low magmatic zircon delta O-18 values (6.2 parts per thousand) and higher apatite LREE (3277-4114 ppm) and Sr (1137-1357 ppm) contents than of arc-type basic rocks were discerned. These characteristics jointly hint the contributions of mantle components. The higher initial T(ti-zr) (>850 degrees C), whole-rock Mg-# (52 to 58), apatite epsilon(Nd)(t) (-9.2 to -6.5) and zircon epsilon(Hf)(t) (-7.6 to 2.5) values but lower zircon delta O-18 values (6.33 to 8.30 parts per thousand) of the later granodiorite porphyry dike than those of the batholith also suggest that mantle material was involved in the generation of the dikes, which is evident by the variational features of zircon and apatite trace elements. In addition, at the zircon Hf <12000 ppm and Eu/Eu* > 0.05, the higher zircon Delta FMQ values (mostly from -1.8 to 2.0) and H2O contents (100-1100 ppm) of the Dachang granitoids than the pure crust-derived S-type granites (Delta FMQ = mostly from -3.7 to -1.5; H2O < 100 ppm) imply that mantle materials involved are relatively rich in water and oxidized. These suggest that the addition of mantle components is conducive to the extraction of Sn from metasedimentary sources, and moderately facilitates the increase of oxygen fugacity which still maintains the incompatibility of Sn in magmas with Delta FMQ < 2. Also, the involvement of mantle components upgrades the H2O contents in S-type magmas, favoring the migration of ore-forming elements from magmas to hydrothermal fluids. The sediment-derived causative granites displayed higher epsilon(Hf)(t) and epsilon(Nd)(t) values with greater Sn tonnages of their associated world-class Sn polymetallic deposits, supporting the opinion that the contributions of mantle components play an important role in the generation of giant Sn deposits.

The world's second-largest Dachang Sn ore field in the southwest of China exhibits genetic connections to the Late Cretaceous highly evolved S-type granitoids (93-91 Ma). In this study, we report the newly identified Eocene granite porphyry dikes with zircon U-Pb ages of 35-33 Ma at the Gaofeng Sn deposit from the Dachang ore field. The petrogenesis and mineralization potential are also constrained by employing whole-rock and zircon geochemical data. These Eocene dikes coincide with the emplacements of granitoids (35-30 Ma) along the Ailaoshan-Red River fault and its neighboring regions, indicating that they could be related to a similar lithospheric extension setting after the Indo-Asian collision. However, unlike those of the latter granitoids (35-30 Ma), which are grouped into I-type granites, the high-silica granite porphyry dikes show elevated ASI values (1.32-1.38) with high P2O5 (0.41-0.44 wt%) and normative-CIPW corundum (4.15-4.71 wt%) contents and could be classified as S-type granites. The strongly negative whole-rock Sr, Ba, and Eu anomalies signify separation of plagioclase and K-feldspar during magma crystallization, which is also confirmed by the zircon trace elements compositions. The Gaofeng Eocene granite porphyry dikes have a high initial zircon Tti-zr of 855 degree celsius, high Ba/Pb ratios (11.5-16.8), and low Pb contents (7.56-9.98 ppm) with low zircon epsilon(Hf)(t) values (-7.4 to -0.6), hinting at the dehydration melting of biotite from the metasedimentary basement. Additionally, the dikes are characterized by low oxygen fugacity (zircon Ce/Ce* <70; Delta FMQ from -6.0 to +0.6 with an average of -2.0) and show evidence of magmatic-hydrothermal interaction (whole-rock Nb/Ta < 5), in line with those of the Dachang Late Cretaceous fertile granites, suggestive of Sn mineralization potential. Therefore, it is recommended that attention should be paid to the Eocene granite porphyry dikes during future prospecting.

The diverse types of Mesozoic intracontinental gold mineralization in the South China Block (SCB) are geneti-cally linked to prolonged oceanic plate subduction. These gold deposits, with estimated resources greater than 2000 tonnes, comprise four gold provinces: Hainan Island, Wuyi-Yunkai Belt, Jiangnan Orogen, and Youjiang Basin. In these provinces, Paleo-Pacific Plate subduction, crustal thickness and composition, structural reac-tivation, and fluid-wall rock reactions collectively controlled the distribution and diverse features of the Meso-zoic intracontinental gold mineralization.Three stages can be identified in the metallogenic evolution of the SCB. (1) Formation of orogenic gold de-posits gradually younging from the coast (Hainan) to the hinterland (Youjiang Basin and Jiangnan Orogen) related to flat-slab subduction of the Paleo-Pacific Plate and clockwise rotation of the SCB between 245 and 200 Ma. (2) Formation of intrusion-related Au-(Sb-W) deposits in the western Jiangnan Orogen in a continental extensional setting in the wake of flat-slab subduction between 210 and 195 Ma prior to the early to middle Jurassic hiatus (190-170 Ma) of high-angle subduction and stagnant slab. (3) Between 170 and 90 Ma, inter-mittent formation of intrusion-related gold deposits in the coastal region (-160 Ma,-100 Ma) and hinterland (-160 Ma, 140-130 Ma), and the formation of Carlin-type gold deposits in the Youjiang Basin (-140 Ma) during episodic extension caused by slab foundering and changes in subduction angle. After 90 Ma, regional differential crustal thinning and denudation determined the extent of uplift and exposure of various types of ore deposits. In stage 1, the quartz vein-type and disseminated orogenic gold deposits hosted in Precambrian rocks, and with a subcrustal source, are related to the reactivation of crust-scale NE-trending faults. In contrast, disseminated orogenic gold deposits hosted in Phanerozoic rocks and influenced by fluid-rock reactions relate to landward propagation of a fold-thrust system. In stage 2, intrusion-related Au-(Sb-W) deposits only formed in intracontinental Precambrian rocks and were controlled mainly by shallow, brittle, and extensional NW-trending structures. Highly fractionated late-stage S-type granite (used sensu lato throughout) complexes controlled the distribution of intrusion-related gold-(polymetallic) deposits in stages 2 and 3. In stage 3, stratabound and disseminated Carlin-type gold deposits are restricted to platform facies carbonate sequences, and intrusion-related gold deposits are structurally related to the reactivation of NE-trending faults. Both are interpreted to have a magmatic-hydrothermal source.The crustal architecture of the four gold provinces exhibits marked differences in crustal thickness, contrasts in rheology, abundance of deep faults, and intensity of mantle-crust interaction. Those gold provinces in the central-southeastern SCB are the result of the reactivation of a paleo-orogen, in contrast to those hosted by deformation systems in shallow crust in the western SCB during the Mesozoic. The Carlin-type and intrusion -related gold deposits are located in regions with more mafic and felsic components, respectively, as indicated by seismic Vp/Vs ratios. However, the spatial distribution of orogenic gold deposits is poorly correlated with that of Vp/Vs ratios, suggesting a subcrustal source.

Late Ordovician–Early Silurian intermediate igneous rocks have been detected in the Dunhuang Block, NW China. These igneous rocks help to constrain the tectonic evolution of the Dunhuang Block and the southern Central Asian Orogenic Belt in the early Paleozoic. We carried out zircon U–Pb dating, whole-rock geochemistry and zircon Hf isotope analyses for the early Paleozoic gneissic diorites from the Sanweishan and northern Huangshuihou areas in the Dunhuang Block. The zircon U–Pb geochronology shows that the emplacement ages of the gneissic dioritic rocks were c. 443–440 Ma. The dioritic rocks show varying SiO 2 (48.1–63.1 wt%) and MgO (1.87–3.52 wt%) contents, with high Mg# (46–52) values and negative Eu anomalies (Eu/Eu* = 0.62–0.94). Zircons in the gneissic diorites from the northern Huangshuigou and Sanweishan areas yield variable ε Hf ( t ) values of −4.4 to +10.4 and −8.6 to −6.2, respectively, coupled with low Rb/Sr (0.04–0.34), Rb/Ba (0.06–0.31) and Al 2 O 3 /(MgO + FeO T ) (0.72–1.47) ratios, indicating that they were predominately generated by disequilibrium melting of the juvenile crust and mixed with ancient crustal and minor mantle melts. In conjunction with previously published data, we propose that the early Paleozoic gneissic dioritic rocks were formed in a continental margin arc setting related to the southward subduction of the Palaeo-Asian Ocean. Our findings suggest that the Dunhuang Block was modified and reactivated by the Paleozoic orogenic events related to the evolution of the Palaeo-Asian Ocean, resulting in extensive Paleozoic magmatism–metamorphism over the whole Dunhuang area. Supplementary material: Analytical methods, U-Pb geochronological data, zircon trace element data, zircon Lu-Hf isotopic compositions, and geochemical data for analysed samples, and additional figures are available at https://doi.org/10.6084/m9.figshare.c.6174601

To constrain the relationship between the plate boundary dynamics and the basin sedimentation in the southwestern South China Block (SCB), we undertook detrital zircon U–Pb–Hf isotope compositions of the Lower‐Middle Triassic turbidite system in the Youjiang Basin and biotite 40 Ar/ 39 Ar thermochronology of the adjacent Lingshan granite. The detrital zircons from Lower Triassic clastic rocks are dominated by age peaks at ~450 Ma and ~1,000 Ma and minor peaks at ~250–260 Ma with negative ε Hf (t) values (−6.4 to −10.1). In contrast, the Middle Triassic group contains more volcanic fragments and displays a different age peak at ~240–287 Ma with ε Hf (t) between −11.9 and 13.2 in addition to the former two peaks. These results suggest a potential provenance associated with juvenile and volcanic components in the adjacent region during the Middle Triassic. A summary of the Triassic tectonothermal history suggests that the eastern Youjiang Basin and Yunkai Terrane were uplifted throughout the Triassic, while the northeastern Indochina Block on the west of the SCB was uplifted mainly during the Middle Triassic. Combined with the palaeocurrent reconstruction, we infer that the turbidite system was filled primarily from east to west during the Early Triassic, mainly controlled by the Palaeo‐Pacific plate subduction. Subsequently, the Middle Triassic turbidite system involved juvenile and volcanic components from the eastern SCB and northeastern Indochina Block in addition to the Early Triassic provenance, as a result of dual impact from the Palaeo‐Pacific plate subduction and Indochina Block collision.

Large-scale eruption of Emeishan flood basalt occurred in the western margin of the Yangtze Craton in a short period during similar to 260Ma. Mafic-ultramafic rocks found in the Panxi area are widely considered to be products of the Emeishan Large Igneous Province (ELIP). However, there is a lack of reports on this kind of rocks in the Songpan-Ganzi area in the northern end of the ELIP. This paper first documents a precise age of the Shuizi pyroxenite in the Danba County. The zircon LA-ICP-MS U-Pb weighted mean age is 260. 7 +/- 3. 3Ma, indicating a representative mafic-ultramafic constituent of the northern end of the ELIP in the Songpan-Ganzi area. Comparing zircon trace elements of the Shuizi pyroxenite with those of picrite in the marginal zone and gabbro in the upper zone of the Panzhihua Fe-Ti-V oxide deposit were conducted. It is found that the Shuizi pyroxenite has similarly high magmatic oxygen fugacity, Delta QFM of 0 similar to 3 and average Ce-N/Ce-N* of similar to 30, to the Panzhihua mafic rocks. The high oxygen fugacity for both is considered to be derived from a mantle lithosphere source which had been metasomatized by subducted oceanic slab materials in the western margin of the Yangtze Craton. Although the Shuizi pyroxenite has high oxygen fugacity, there is less obvious Fe-Ti oxide saturation and precipitation here. This could be attributed to its relatively low degree of crystallization and differentiation. In contrast, the Panzhihua mafic-ultramafic intrusion experienced higher degree of titanomagnetite and plagioclase fractional crystallization, accompanied by a massive Fe-Ti-V oxide mineralization.

The occurrence of adakitic rocks can provide insight into the evolution of continental crust and deep geodynamic processes in subduction zones. In this paper, we investigated zircon U-Pb ages and Hf isotope, whole-rock major and trace elements, and whole-rock Sr-Nd-Pb isotopes of the Lianghu quartz diorites and Shigong monzogranites in the Dunhuang Block, to understand their petrogenesis and tectonic setting as well as the tectonic evolution of the Dunhuang Block in the early Paleozoic. LA-ICP-MS zircon U-Pb dating results suggest that the Lianghu quartz diorites and Shigong monzogranites were emplaced at ca. 455 ± 3 Ma and 431 ± 3 Ma, respectively. The Ordovician quartz diorites exhibit relatively high Sr (734–904 ppm) contents, negative-to-negligible Eu anomalies (Eu/Eu* = 0.87–0.99), high Sr/Y (52.5–124) ratios, but low Yb (0.68–1.32 ppm) and Y (7.27–14.0 ppm) contents. Moreover, they exhibit relatively high Mg# (52.0–54.7) values, Cr (23.1–88.0 ppm) and Ni (15.0–53.3 ppm) contents, similar to those of adakitic rocks originating from subducted oceanic crust. The quartz diorites display low initial 87Sr/86Sr (0.703464–0.704783), negative εNd(t) of −3.2 to −1.3, and positive εHf(t) of +3.8 to +8.0, with two-stage model ages for the Nd and Hf systems of 1.12 to 1.09 Ga and 1.17 to 0.91 Ga, respectively, indicative of a heterogeneous magma sources. They have relatively high radiogenic 206Pb/204Pb(t) (18.219–19.066), 207Pb/204Pb(t) (15.616–15.669), and 208Pb/204Pb(t) (39.042–39.198), signifying that some subduction-related materials (e.g., ocean island basalts) may be involved as sources. These characteristics indicate that the Lianghu quartz diorites were derived from the partial melting of subducted oceanic slabs (sediments + fluids), and that they underwent subsequent interaction with peridotite in the mantle wedge, with limited assimilation of crustal materials during magma ascent. The Silurian monzogranites contain high Sr content (655–674 ppm) but very low contents of Y (2.49–4.19 ppm) and Yb (0.24–0.37 ppm), yielding high Sr/Y ratios (161–263); those values, together with low MgO (0.30–0.41 wt.%), Mg# (40.6–41.4), Cr (2.39–3.28 ppm), and Ni (2.19–2.95 ppm) contents, resemble those of thickened lower crust-derived adakitic rocks. They show εHf(t) and εNd(t) values of −2.5 to +3.0 and −3.6, with the respective two-stage model ages of 1.55 to 1.20 Ga and 1.32 Ga. Their low Pb values, 206Pb/204Pb(t) = 18.184, 207Pb/204Pb(t) = 15.595, and 208Pb/204Pb(t) = 37.717, also suggest addition of minor mantle-like melts. These geochemical features indicate that the parent magmas of the monzogranites originated either from the melting of heterogeneous crustal sources, or through mixing of thickened juvenile crust, Mesoproterozoic crust materials, and minor mantel-derived materials in the stability field of garnet-bearing amphibolite. Given the coeval regional magmatism and tectonic setting, we propose that the continental crust thickening of the Dunhuang Block began roughly in the late Ordovician (~35 km) and culminated in the early Silurian (~50–55 km), as evidenced by the La/Yb ratios of quartz diorites (12.2–25.2) and monzogranites (57.6–60.9). The corresponding transition of the tectonic regime from subduction to collisional setting occurred at ~440 Ma. The Dunhuang Block could undergo thickening processes associated with underplating of mantle-derived magmas during subduction of the southern Paleo-Asian Ocean, and subsequently collided with the Shibanshan terrane (a Paleozoic continental arc) along the southern Beishan orogen at ca. 440–430 Ma. Our results show that the Dunhuang Block represents a continental arc in the early Paleozoic, and was involved in the Paleozoic orogenesis of the Central Asian Orogenic Belt.

The Debao deposit, with stratiform orebodies in Middle-Upper Cambrian carbonate rocks, is a rare Early Paleozoic skarn copper deposit in the South China Block. Garnet U-Pb dating yielded a lower intercept 206Pb/238U date of 438.8 ? 7.3 Ma, which is coeval with the related granite (439 _ 441 Ma). Skarns contain garnets with andraditic compositions (Ad53_93Gr4_46Py1_8) and clinopyroxene (Hd5_11Di89_94Jo0_1 and Hd52_85Di13_46Jo1_4) with low Mn/Fe ratios (<0.1), showing typical mineral compositions of Cu skarn deposits. The proximal garnet skarn mainly developed at the bottom and both sides of the orebody, while distal pyroxene skarn developed in its interior and upper parts. The garnets in the bottom of the orebodies contain more andraditic compositions than their upper parts. The prograde skarn minerals have a range of ?18Ofluid values from 8.81 to 9.53?, and the sulfide minerals of the main ore stage have a range of ?34S values from -2.40 to 2.57?, both suggesting a magmatic origin of the ores. In the Debao deposit, hydrothermal magnetite from different skarn zones contains substantial amounts of Al, Sn, Ga, Mn, Mg, Ti, Zn, Co, V, and Ni. The content of Al and Ti in the magnetite, which was considered to derive from the wall rock due to fluid-rock interaction, was positively correlated with temperature. Magnetite in the retrograde skarn stage from the proximal garnet skarn zone contains more Ti and V than that from the distal pyroxene skarn zone, indicating a gradual decrease in temperature and increase in oxygen fugacity of the ore-forming fluid in this stage. The magnetite has higher Sn content (mainly hundreds to thousands of ppm) than normal skarn deposits, implying that high oxygen fugacity occurs during the retrograde skarn stage. Subsequently, the formation of magnetite led to a decrease in the oxygen fugacity of the ore-forming fluid. The decrease of oxygen fugacity and temperature provided favorable conditions for subsequent precipitation of Cu sulfides. Minor vein-type Cu mineralization related to late magmatic fluid extraction of sulfur from the sedimentary strata was recognized. All geologic and geochemical data suggested that the deep skarn in the region transformed from Early Paleozoic carbonate has copper mineralization potential.

Late Paleozoic granitoid rocks hold critical information regarding continental crustal growth and evolution of the Dunhuang Block at the southernmost margin of the Central Asian Orogenic Belt (CAOB). Here, we report new zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemistry and Sr-Nd-Pb isotopic compositions for Devonian granitoid rocks and dacite porphyry in the Dongshuigou area of the Dunhuang Block, NW China. Petrographic investigation suggests that the Dongshuigou composite pluton, mainly consisting of quartz diorite, granodiorite, and biotite granite, was emplaced in the middle Devonian (ca. 390-380 Ma), whereas the dacite porphyry intruded into the granodiorite in the late Devonian (ca. 367 +/- 4 Ma). The quartz diorite and granodiorite are similarly sodic, middle-K calc-alkaline, high Mg-# (48.5-49.8) and Cr-Ni contents, enriched in LREE and LIIE (e.g., Rb, Ba, and P), and depleted in HFSE (e.g., Na and Ta), indicative of typically arc-like geochemical signatures. The quartz diorite has positive epsilon(Nd)(t) (+0.38), variable epsilon(Hf)(t) values (+3.12 to +10.7), juvenile Nd (1.04 Ga), and Hf model ages of 0.83 to 1.15 Ga. In comparison, the granodiorite displays negative epsilon(Nd)(t) values (-0.73) closed to the chondrite line, positive epsilon(Hf)(t) values (+3.75 to +8.36), juvenile Nd (1.12 Ga), and Hf model ages of 0.83 to 1.12 Ga. Both plutonic rocks show low initial Pb isotopes similar to those of typical lower crust-derived rocks. Our data indicate that the diorites and granodiorites were derived from partial melting of the juvenile lower crust with addition of minor mantle materials. The high-K, calc-alkaline dacite porphyry exhibits relatively high SiO2 and K2O contents, moderate Mg-# (45.2-46.2) values, enrichment in Rb, U, Pb, and K, depletion in Nb, Ta, and Ti, and low Sr and Y abundance. These geochemical characteristics are similar to those of lower crust-derived arc-related rocks, including the development of abundant inherited zircons, implying that the dacite porphyry was likely generated by a mixed source of the mafic lower crust and minor metasomatized mantle materials. The biotite granites are characterized by high Sr contents (481-542 ppm) and Sr/Y ratios (76.0-98.4), low Y (5.37-6.51 ppm) and Yb (0.50-0.56 ppm) contents, and high Mg-# values (55-56) and Cr-Ni contents, showing geochemical affinities of adakitic rocks. They have positive epsilon(Nd)(t) (+2.97 to +3.00), variable epsilon(Hf)(t) values (-6.05 to +12.4; mostly >0) with Nd and average Hf model ages of 0.82 Ga and 0.92 Ga, respectively. The biotite granites exhibit low initial Pb-206/Pb-204, Pb-207/Pb-204, and Pb-208/Pb-204 ratios of 18.336-18.339, 15.622-15.622, and 38.478-39.510, respectively, indicating that some subduction-related materials, such asmature arc primitive or ocean island volcanic rocks could have been added to the magma source. The biotite granites were likely derived from partial melting of subducted oceanic crust, which was modified by interactions with mantle wedge, with the addition of minor Mesoproterozoic materials during magma ascent. By synthesizing with the regional geology, we suggest that the middle Devonian granitoids and the late Devonian dacite porphyry in the Dongshuigou are arc/subduction-related rocks that formed in a continental arc setting. Taken together, Devonian arc-related magmatic events in the Dunhuang Block indicate significant crustal growth that was accompanied with minor reworking of ancient lower crust. (C) 2021 Elsevier B.V. All rights reserved.

The Dunhuang Block in the Central Asian Orogenic Belt (CAOB) consists of Archean to Paleoproterozoic crystalline basement, along with Paleozoic complexes that are related to the evolution of the CAOB. A current main controversy concerns whether the whole Dunhuang Block has experienced the Paleozoic tectonothermal events. Titanite, a common U–bearing accessory mineral in igneous and metamorphic rocks, is susceptible to magmatic and metamorphic processes, and thus tends to record relatively late tectonothermal events for metamorphic rocks. In this study, we conducted LA–ICPMS U−Pb dating on titanites from the Archean to Paleoproterozoic rocks in the Dunhuang Block. The titanites are likely metamorphic in origin and yielded U–Pb ages of 409−309 Ma. These ages can be divided into two major groups at 409−390 Ma and 354−309 Ma, corresponding to an early-stage retrograde of high–grade metamorphism and a later-stage magmatism, respectively. Overall data and regional geology indicate that the whole Dunhuang Block has been intensively reworked by the Paleozoic tectonothermal events, leading to metamorphic and magmatic overprints of the early Precambrian basement rocks during the evolution of the CAOB in the Paleozoic. Therefore, the Dunhuang Block should not be considered as an independent Paleozoic orogenic belt. More importantly, our study demonstrates that titanite U–Pb dating can be used as a potential geochronologic tool to reveal late tectonothermal events of the reworked Precambrian metamorphic terranes.

The geochemical composition and temporal evolution of A-type granites may hold key information regarding critical geodynamic processes that occurred during the evolution of the continental crust. Moreover, these aspects may provide an indication of when orogenic processes ended and craton formation/stabilization began in Early Precambrian blocks. In this study, we report the results of zircon U-Pb ages, Hf isotope data and wholerock geochemistry for the Proterozoic Huoyanshan potassic granites in the Dunhuang Block, northwest China. Zircon U-Pb dating reveals that the Huoyanshan granites were emplaced at ca. 1791-1786 Ma, representing a Late Paleoproterozoic magmatism event. The granites have high SiO2 (70.71-72.20 wt%), total alkali contents (K2O + Na2O = 8.81-8.96 wt%; K2O/Na2O = 1.57-1.66), TiO2/MgO ratios (2.19-2.57), low CaO (0.77-1.27 wt%), MgO contents (0.12-0.16 wt%), and Mg-# values (7.72-8.67), with A/CNK ratios of 0.96-1.04, pointing to alkaline and metaluminous to weakly peraluminous affinities. These granites are characterized by high total rare-earth element concentrations (Sigma REE = 419-755 ppm) and variable (La/Yb)(N), values (8-24) with significantly negative Eu anomalies (Eu/Eu* = 0.31-0.42). The primitive mantle-normalized trace element patterns suggest that the Huoyanshan plutons are depleted in Ba, Nb, Ta, Sr, P, and Ti, but enriched in Rb, Th, and Pb. Additionally, the granites have a high zirconium saturation temperature of 855-897 degrees C, with an average of 878 degrees C. These geochemical characteristics indicate that Huoyanshan potassic granites are an aluminous A-type granite, and further classified as A(2)-type. Together with the zircon Hf isotope data (epsilon(Hf)(t) = - 11.21 to - 2.76), indicates that these granites were generated from a crustal source. The heterogeneous Hf isotope compositions in zircons are principally caused by the disequilibrium melting of Zr-bearing sources. In addition, two-stage Hf model ages of zircons from the granites are ca. 2.6-3.1 Ga and plot on the average crustal evolution trend of Archean tonalite-trondhjemite-granodiorite (TTG) gneiss (similar to 2.5 to 3.0 Ga) in the Dunhuang Block. Thus, we propose that A-type granites in the study area were generated from the disequilibrium partial melting of Archean tonalitic to granodioritic rocks under high-temperature and low-pressure conditions according to their low Al2O3 + CaO + Na2O + K2O (molar) values and high 10000 x Ga/Al values ( > 2.9). Subsequently, the magma experienced prominent fractional crystallization of K-feldspar, plagioclase, orthopyroxene, and/or magnetite. Our results, with available data, suggest that the Huoyanshan granites formed in a tectonic transform regime within a collisional to extensional setting, and serve as a precursor for the formation and stabilization of the Dunhuang Block during the Late Paleoproterozoic. Furthermore, it is probable that the post-collisional magmatism event at ca. 1.79 Ga in the Dunhuang Block was closely related to the assembly of the Columbia supercontinent.

The North China Craton (NCC) is characterized by major ca. 2.5 Ga tectonothermal events, which is markedly different from most other typical cratons worldwide. Whereas, ca 2.7 Ga rocks are sporadically exposed in the whole craton, and only have been identified in several localities. In this contribution, we report new discovery of ca. 2.7 Ga rocks from the western Huixian in the NCC. Zircon U-Pb dating reveals their protoliths were emplaced between 2714 and 2704 Ma. The rocks are tonalitic gneisses in composition, and present similar geochemical characteristics to the Archean TTG suites and Phanerozoic high-SiO2 adakites worldwide. Zircons from the three tonalitic gneisses yield variable positive epsilon(Hf)(t) values of 2.3-6.7, 4.2-8.7, and 3.3-6.3, with Hf model average ages of ca. 2848 Ma, ca. 2838 Ma, and ca. 2840 Ma, respectively. The measured zircon delta O-18 values range from 5.5 parts per thousand to 6.2 parts per thousand, 5.1 to 6.1 parts per thousand, and 5.2 to 6.2 parts per thousand, with weighted mean values of 5.7 parts per thousand, 5.7 parts per thousand, and 5.8 parts per thousand, respectively, all of them overlap with the mantle range within two sigma uncertainty limits. The Hf-O isotope compositions in zircons from the tonalitic gneisses indicate that their protoliths originated in a juvenile crustforming event at ca. 2.7 Ga. Available data suggest ca. 2.7 Ga is a major period of crustal growth in the NCC. Geochemical signatures of the ca. 2.7 Ga tonalitic gneiss reflect that their protoliths formed by partial melting of hydrated mafic rocks with variable proportions of the amphibole and garnet residues to be left behind in the residuum but absence of plagioclase and rutile in their source. The rocks are classified as HP-TTG, their protolith formed under amphibolite-facies conditions. It is noted that the ca. 2.7 Ga tonalitic gneisses in Huixian display low MgO (< 2 wt%), Ni (16.6-23.5 ppm), and Cr (14.6-28.8 ppm) as well as uniform positive epsilon(Hf)(t) values and mantle-like zircon delta O-18 values, indicating that the protolith magma was likely produced by partial melting of a thickened lower oceanic crust.

Objective Rodinia was a supercontinent that comprised nearly all the current existing continents/blocks on Earth to form a coherent large landmass during the Meso-Neoproterozoic. Thus, discovery of Meso-Neoproterozoic rocks in a certain Precambrian block can provide important clues for studying the assembly and break-up history of Rodinia. The Dunhuang Block, located at the southernmost part

The Youjiang Basin in the western part of the South China Block (SCB), preserves the records of the tectonic history from Tethyan, through Paleo-Pacific to Tibetan domains, with coeval formation of diverse types of giant metallic deposits. The prolonged tectonic evolution and its control on the genesis and spatio-temporal distribution of giant metallic deposits in the Youjiang Basin provide a window for a holistic understanding of the tectono-metalligenesis of SCB. Six tectono-metallogenic stages can be recognized in the geological evolution of the basin and their relationship to the geodynamic evolution of the surrounding tectonic units. Subsequent to the closure of the Proto-Tethyan Ocean and collision between the SCB and the Gondwana continent, a late Ordovician to early Silurian intracontinental orogeny along the southern margin of the basin resulted in the formation of Silurian Cu and W skarn deposits. During Devonian to Carboniferous, during the Paleo-Tethyan spreading, the basin experienced rifting and development of a passive continental margin, when sedimentary Mn carbonate ores were deposited in basin facies sequences in the southern part of the basin. On the northern margin, bauxite karsts formed in carbonate rocks within continental-margin sequences. In the Late Permian, the Paleo-Pacific oceanic plate was subducted below the SCB, which most likely induced migration of the coeval Emeishan mantle plume towards the plate margin. Arc volcanism resulted in voluminous ash falls on the carbonate platform and these were subsequently transformed into bauxite in the southern part of basin. Following this, Triassic intraplate shortening induced thin-skinned crustal deformation with associated formation of orogenic Au deposits throughout the basin. In the Jurassic, the Youjiang Basin experienced slab delamination, during which MVT PbZn deposits formed along the northern margin, and clusters of WSn skarns were generated at the centre of the delamination zone on the eastern margin of the basin. Subduction retreated southwards in the Cretaceous, resulting in the formation of Carlin-type Au deposits in the northern part of the basin, and Sn and Cu skarns and associated carbonate replacement PbZn deposits in the central and southern parts. Cenozoic regional denudation and climate change in response to the southeastward propagation of Tibet caused brittle deformation of pre-existing bauxite and Mn orebodies and their further enrichment. The overlap among Paleo-Tethyan, Paleo-Pacific and Tibetan tectonic regimes during the evolution of the Youjiang Basin generated a diverse range of mineral deposit types, including orogenic and Carlin-type Au deposits, both carbonate-replacement and MVT-type PbZn deposits, sedimentary Mn‑carbonate deposits and bauxite in both passive and active continental margins.

The Taihua Complex is exposed in the southern North China Craton (NCC), it has experienced a long and complicated history of multiple crustal growth, magmatism, metamorphism and deformation during the early Precambrian. Abundant leucosomes are widely distributed within the migmatites of the Taihua Complex, which occurred as irregular lenses, blocks, layers or dikes with several thickness of millimeters to tens of centimeters wide. Meanwhile, former presence of melt and typical microstructures related to partial melting also can be recognized in the thin sections under the microscope, those provide compelling evidences that the Taihua Complex has extensively suffered partial melting, and can be regarded as the best target to decipher multistage anatexis during metamorphism as well as assembly of the whole NCC. However, the timing and nature of the partial melting in the Taihua Complex have not been well studied up to now. In this contribution, we present an integrated in situ zircon U-Pb ages and Hf isotope compositions for the Paleoproterozoic migmatites from the Taihua Complex in the southern NCC. Both the metasedimentary and metamorphized plutonic rocks of the Taihua Complex have extensively suffered partial melting. The ca. 2.50 Ga magmatic zircons or inherited magmatic cores from the migmatites and leucosomes present similar Hf isotope composition to those of the contemporaneous depleted mantle at ca. 2.50 Ga, suggesting that ca. 2.50 Ga is a major period of crustal growth in the southern NCC as well as the whole NCC. The ages of metamorphic zircons obtained from leucosomes, melanosomes and migmatites show a large time interval of 1909-1798 Ma, indicating that the Taihua Complex has experienced a persistence of partial melting event during Late Paleoproterozoic that lasted more than 100 Ma. The crustal anatexis in the southern NCC probably occurred during the post-peak upper amphibolite- to granulite facies stage with melting temperature of at least 652-753 degrees C. The decompression melting and widespread migmatization of the Taihua Compelx are probably due to extension related to exhumation of the previously thickened crust during Paleoproterozoic collision between the Eastern and Western block, or between the Southern Archean Block and other micro-continents. The main collision-related assembly and crustal thickening events in the southern NCC likely occurred at ca. 1.95 Ga, rather than ca. 1.85 Ga as previously believed.