Central Great Xing Research Articles

Petrogenesis and Tectonic Setting of the Early and Middle Jurassic Granitoids in the Chaihe Area, Central Great Xing’an Range, NE China

To ascertain the Early-to-Middle Jurassic tectonic setting in the central Great Xing’an Range, this study investigated the Early and Middle Jurassic granitoids exposed in the Chaihe area in the central Great Xing’an Range based on isotopic chronology and petrogeochemistry. The results of this study show that the Early and Middle Jurassic granitoids have emplacement ages of 179–172 Ma. Moreover, the Early and Middle Jurassic granitoids are high-K calc-alkaline unfractionated I-type granitoids and high-K calc-alkaline fractionated I-type granitoids, respectively. The magma sources of the Early and Middle Jurassic granitoids both originated from the partial melting of newly accreted lower crustal basaltic rocks. Meanwhile, the Middle Jurassic magma sources were mixed with mantle-derived materials or ocean-floor sediments formed by the dehydration and metasomatism of subducted slabs. The Early and Middle Jurassic granitoids in the study area were formed in the subduction environment of the oceanic crust, in which the Mongol-Okhotsk oceanic plate was subducted southward beneath the Eerguna and Xing’an blocks. Moreover, the Siberian plate began to collide and converge with northeast China during the Middle Jurassic.

Protracted extraction of high-silica melts from an upper-crustal magma reservoir recorded by the Wuchagou volcanic rocks in central Great Xing'an Range, NE China

High-silica volcanic rocks and their plutonic counterparts carry critical information concerning the evolution of shallow magmatic systems and construction of silicic upper continental crust, yet their origins remain debatable. Here, we examine high-silica volcanic rocks from the Lower Cretaceous Manitu and Baiyin'gaolao formations of the Wuchagou volcanic field, central Great Xing'an Range (GXR), to constrain the genesis of these high-silica volcanic rocks and the evolution of the Wuchagou magmatic system. Geochronological data suggest that the Manitu and Baiyin'gaolao volcanic rocks represent a prolonged eruption from the Wuchagou magmatic system, spanning Period I (135–129 Ma ) and Period II (127–122 Ma ) magmatism in the central GXR. Their slightly depleted ε Nd (t) values and relatively young model ages coincide with a juvenile crustal origin. We suggest that the Manitu and Baiyin'gaolao high-silica volcanic rocks are the evolved compositions of their coexisting intermediate rocks given the similarities in both formation age and Sr-Nd isotopic composition and systematic geochemical variations. Clinopyroxene- and amphibole-based thermobarometers respectively yield low average pressures of ~3.3 kbar and ~ 1.8 kbar with low temperatures of ~1013 °C and 875 °C. Also, Clinopyroxene- and amphibole-based hygrometry yield relatively high H 2 O contents of ~2.7–4.1 wt% and ~ 3.1–4.6 wt%. Together, they indicate the presence of a hydrous upper-crustal magma reservoir feeding the eruptions of the Manitu and Baiyin'gaolao high-silica volcanic rocks. Combining the behavior of highly incompatible elements (Rb and Th) with trace element modeling results, we show that the Wuchagou high-silica volcanic rocks formed by protracted extraction of high-silica melts in the upper crust, with complementary residual cumulates partially disguised in the Early Cretaceous felsic plutons in the central GXR. Our results highlight the significance of prolonged upper-crustal differentiation of magmas derived from juvenile crust in the development of the high-silica upper continental crust. • High-silica volcanic rocks extracted from a long-lived upper-crustal reservoir. • Complementary residual cumulates disguised in contemporaneous felsic plutons. • Crystal-melt segregation contributed to development of high-silica upper crust.

Geochronology, geochemistry, and petrogenesis of Early Cretaceous highly differentiated I-type granites in the central Great Xing’an Range, northeastern China

In this study, we undertook zircon U–Pb dating and Hf isotopic and whole-rock geochemical analysis of Mesozoic granites from the Zhalantun and Arxan areas of the Great Xing’an Range, northeastern China. Zircon U–Pb dating of four samples indicates they formed in the Early Cretaceous (ca. 140.7–130.0 Ma). Geochemically, the samples have high silica (74.00–77.29 wt.%) and total alkali (8.52–8.90 wt.%) and low CaO (0.21–0.71 wt.%), MgO (0.06–0.48 wt.%), and P2O5 (0.01–0.06 wt.%) contents and exhibit the weakly peraluminous (A/CNK = 0.98–1.06) and high-K calc-alkaline characteristics, with highly differentiated I-type granite affinities (differentiation index = 93.19–96.93). The studied granites are enriched in light rare earth and large ion lithophile elements and depleted in heavy rare earth and high field strength elements. Their zircon εHf(t) values are mainly positive (+2.49 to +11.64) and yield two-stage Hf model ages of 1023–445 Ma. The geochemical and isotopic data indicate they might have been derived from the partial melting of medium- to high-K basaltic crust material during the Mesoproterozoic to Phanerozoic. They underwent fractional crystallization in the magma evolution process, and K-feldspar and plagioclase were the major crystallization phases. Combined with the temporal–spatial migration of the Mesozoic magmatic events in the whole northeastern China, we propose that the generation of Early Cretaceous highly differentiated I-type granites in the central Great Xing’an Range was associated with the delamination effect caused by the roll-back of the Paleo-Pacific plate.

Petrogenesis and tectonic implications of Early Cretaceous granite porphyry in the Taipingtun area, central Great Xing'an Range, NE China

New LA‐ICP‐MS zircon U–Pb geochronology, whole‐rock geochemistry and Hf isotopic data have been studied on the Taipingtun granite porphyry to determine its petrogenesis and constrain the tectonic setting of the central Great Xing'an Range, northeastern China, during the Early Cretaceous. The results of zircon U–Pb dating suggest that the Taipingtun granite porphyry was emplaced during the Early Cretaceous (122–123 Ma). Geochemically, the granite porphyries have high contents of SiO2 (75.76–78.66 wt%) and (K2O + Na2O) (7.14–8.29 wt%), and low Al2O3 (11.09–12.81 wt%) and CaO (0.15–0.29 wt%), indicating peraluminous and high‐K calc‐alkaline features. Additionally, these rocks are characterized by strong Th, U, K, and Rb enrichment; Ba, Sr, P and Ti depletion; high Ga/Al ratios (10,000*Ga/Al = 2.60–4.92) and negative Eu anomalies (δEu = 0.02–0.13). According to the zircon saturation thermometer results, zircon saturation temperatures range from 756 to 959°C with an average of 823°C, displaying high magmatic temperature for the parental magma. Based on these geochemical characteristics, it can be reasonably inferred that the initial composition of the Taipingtun granite porphyry melts exhibited an A‐type magmatic affinity. Furthermore, zircon grains within the Taipingtun granite porphyry have εHf(t) values of 7.12 to 10.99 and TDM2 model ages of 476–726 Ma. The Ba/La (average 3.89), Nd/Th (average 2.25), Zr/Hf (average 22.55), Ti/Zr (average 2.96) and Rb/Sr (average 4.21) values display the characteristics of crust‐derived magmas. Moreover, these rocks have obviously negative Eu anomalies (average 0.13) and relatively high Y (average 37.83 ppm) and Yb (average 4.15 ppm) contents, suggesting the magmas are generated in a low‐pressure environment. Thus, we consider the primary magmas of the Taipingtun granite porphyry may have been predominantly derived from the partial melting of juvenile crustal rocks at low pressure. Combined with the regional geological data, we suggest that the Taipingtun granite porphyry was formed in an extensional tectonic environment, and possibly related to the subducted Palaeo‐Pacific Ocean Plate in the Early Cretaceous.

Petrogenesis and tectonic implications of Late Triassic dikes from the Suolun within the central Great Xing’an Range, NE China: constraints from geochronology and geochemistry

Petrogenesis and tectonic implications of Late Triassic dikes from the Suolun within the central Great Xing’an Range, NE China: constraints from geochronology and geochemistry

Petrogenesis and Tectonic Setting of Early Cretaceous Intrusive Rocks in the Northern Ulanhot Area, Central and Southern Great Xing’an Range, NE China

Abundant Early Cretaceous magmatism is conserved in the central and southern Great Xing’an Range (GXR) and has significant geodynamic implications for the study of the Late Mesozoic tectonic framework of northeast China. In this study, we provide new high-precision U–Pb zircon geochronology, whole-rock geochemistry, and zircon Hf isotopic data for representative intrusive rocks from the northern part of the Ulanhot area to illustrate the petrogenesis types and magma source of these rocks and evaluate the tectonic setting of the central-southern GXR. Laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating showed that magmatism in the Ulanhot area (monzonite porphyry: 128.07 ± 0.62 Ma, quartz monzonite porphyry: 127.47 ± 0.36, quartz porphyry: 124.85 ± 0.34, and granite porphyry: 124.15 ± 0.31 Ma) occurred during the Early Cretaceous. Geochemically, monzonite porphyry belongs to the metaluminous and alkaline series rocks and is characterized by high Al2O3 (average 17.74 wt.%) and TiO2 (average 0.88 wt.%) and low Ni (average 4.63 ppm), Cr (average 6.69 ppm), Mg# (average 31.11), Y (average 15.16 ppm), and Yb (average 1.62 ppm) content with enrichment in Ba, K, Pb, Sr, Zr, and Hf and depletion in Ti, Nb, and Ta. The granitic rocks (e.g., quartz monzonite porphyry, quartz porphyry, and granite porphyry) pertain to the category of high-K calc-alkaline rocks and are characterized by high SiO2 content (>66 wt.%) and low MgO (average 0.69 wt.%), Mg# (average 31.49 ppm), Ni (average 2.78 ppm), and Cr (average 8.10 ppm) content, showing an affinity to I-type granite accompanied by Nb, Ta, P, and Ti depletion and negative Eu anomalies (δEu = 0.57–0.96; average 0.82). The Hf isotopic data suggest that these rocks were the product of the partial melting of juvenile crustal rocks. Notably, fractionation crystallization plays a crucial role in the process of magma emplacement. Combining our study with published ones, we proposed that the Early Cretaceous intrusive rocks in the Ulanhot area were formed in an extensional tectonic background and compactly related to the subduction of the Paleo-Pacific Ocean plate.

Products of an Early Cretaceous extensional mechanism in the central Great Xing'an Range: Felsic plutons in the Zhalantun area and their parental magma compositions and diagenetic processes

Late Mesozoic extensional mechanisms in the Great Xing'an Range (GXR) and relevant crust–mantle interactions are complicated, which result in widespread magmatisms with diverse parental origins and petrogenesises. In this paper, we present the lithology, whole‐rock geochemistry, and zircon U–Pb–Lu–Hf isotopes for granodiorite‐monzogranite rocks (GM) and their enclaves of quartz monzodiorites in the Zhalantun area, east of central GXR. Zircon U–Pb dating results reveal that both GM rocks and their enclaves of quartz monzodiorites yield a nearly identical crystallization age of ~125 Ma. The GM rocks exhibit weak peraluminous and high‐K calc‐alkaline compositions with high SiO2, Na2O + K2O, and Al2O3 contents, and low MgO, Mg#, Fe2O3T, and TiO2 contents, which are characterized by fractionated REE patterns, relatively strong negative Eu anomalies, enrichments of LILEs (e.g., Rb, Ba, and K), and depletions of Nb, Ta, P, and Ti. The parental origins for GM samples were juvenile crustal materials, with positive zircon εHf(t) values of +2.5 to +12.9. The whole‐rock and zircon geochemical simulations limit slightly lower GM magma crystallization temperatures (TTi‐Zrn) of 683–824°C and relatively more oxidizing conditions (log(fO2) = FMQ+7.6–FMQ‐6.8), and further confine that they were probably formed by ~10–35% degrees of fluid‐present partial melting of lower to middle crustal materials, with fractional crystallization and/or residual mineral phases of plagioclase, amphibole, clinopyroxene, and garnet. By contrast, the enclaves of quartz monzodiorites possess lower SiO2 and Na2O + K2O compositions, but higher MgO, Mg#, Fe2O3T, and TiO2 values, which are consistent with metaluminous–weak peraluminous and high‐K calc‐alkaline series. All quartz monzodiorites exhibit sub‐parallel right‐declined REE patterns, negligible to none Eu anomalies, enrichments of LILEs, and depletions of Nb, Ta, and Ti. Combined with mineral morphology and disequilibrium structures, the whole‐rock geochemical and Hf isotopic simulations imply that parental magmas for quartz monzodiorites were hybrid mixtures between ~50% host GM acid magmas and ~50% ancient crust compositions, with a wide range of zircon εHf(t) of +14.0 to −7.7, slightly higher TTi‐Zrn of 710–835°C, and lower log(fO2) of FMQ+8.2–FMQ‐10.5. Taken together, felsic plutons in the Zhalantun area correspond to an episode of extensional mechanism‐related crust–mantle interactions, which might be induced by either the Mongol‐Okhotsk domain or Palaeo‐Pacific tectonic domain, or both of them.

Origin of the Erdaohe Ag–Pb–Zn deposit, central Great Xing’an Range, northeast China: Constraints from fluid inclusions, zircon U–Pb geochronology, and stable isotopes

The large-scale Erdaohe Ag–Pb–Zn deposit in the central Great Xing’an Range, China, contains > 9.04 Mt of ore reserves. The deposit consists of skarn-type Ag–Pb–Zn orebodies located within a contact zone that is mainly between an Early Cretaceous porphyritic granite and Jurassic calcareous tuff. The deposit records four stages of formation, which are skarn, early quartz–sulfide (disseminated ores), late quartz–sulfide (veined ores), and carbonate stages. Fluid inclusion microthermometry indicates that skarn stage fluids were higher temperature (330 °C to > 500 °C) and more saline (up to 59.8 wt% NaCl equivalent) than the early quartz–sulfide (250 °C–300 °C, <36.1 wt% NaCl equivalent) and late quartz–sulfide stage (160 °C–220 °C, <32.1 wt% NaCl equivalent) fluids. Fluid inclusions of the carbonate stage record even lower temperatures (150 °C–170 °C) and have generally low salinity (2.1–5.1 wt% NaCl equivalent). Raman microprobe data indicate that these fluids are dominated by H2O–NaCl ± CO2 system phases. Sulfides formed during the early and late quartz–sulfide stages of mineralization have a relatively narrow range of δ34S values (4.4‰–8.4‰) that are indicative of sulfur derived from a magmatic source. Quartz samples from the early and late quartz–sulfide stages have δ18Ofluid values of 0.1‰–2.1‰ and from − 5.0‰ to − 3.2‰, respectively, suggesting that the mineralizing fluids were originally magmatic with later stage mineralization involving the addition of meteoric water. LA–ICP–MS U–Pb dating of zircons from the mineralization-related porphyritic granite yielded a weighted mean age of 131.4 ± 0.3 Ma (MSWD = 1.5), indicating that the deposit formed during the Early Cretaceous. Deposit formation involved an aqueous fluid that was exsolved during the final crystallization of the porphyritic granite and ascended along fracture zones until it reacted with Ca-rich wall rocks, cooled to < 300 °C, and boiled under hydrostatic conditions. This caused a decrease in temperature and sulfur fugacity in the ore-forming fluid system, which triggered Ag–Pb–Zn mineralization.

Zircon U-Pb dating and Hf isotopic compositions of intrusions in the Erdaohe silver-lead-zinc deposit, Inner Mongolia and the metallogenic process of the deposit

二道河银铅锌矿为大兴安岭中段最新发现的一处大型矽卡岩型矿床。银铅锌矿的形成与矿区多期岩体密切相关，矿体主要赋存于矽卡岩、大理岩及细粒花岗闪长岩内。本文对矿区主要岩体及石榴子石矽卡岩开展了锆石LA-ICP-MS U-Pb年代学、Hf同位素研究和石榴子石电子探针分析，获得了绿帘石化细粒花岗闪长岩、绿帘石化细粒闪长岩、花岗斑岩的²⁰⁶Pb/²³⁸U加权平均年龄分别为506±4.3Ma、213±2.8Ma和128±1.1Ma。二道河矿区石榴石矽卡岩与绿帘石矽卡岩常呈相互穿插关系，闪锌矿、方铅矿等矿石矿物具有重结晶特征，矽卡岩矿物石榴子石电子探针分析结果显示在矿区至少存在两期不同性质的流体活动，表明二道河银铅锌矿至少经历了两期以上的矿化事件。获得的三类岩体的锆石ε_Hf（t）值分别为0.9~6.9、8.3~15.1和7.9~14.1，对应的二阶段模式年龄（t_DM2）分别为1.6~1.1Ga、0.8~0.3Ga和0.8~0.3Ga，表明这些花岗岩类均来源于新生地壳部分熔融，它们的成因可能分别与额尔古纳地块和兴安地块的拼合、蒙古-鄂霍茨克洋闭合及古太平洋板块俯冲有关。这些构造体系的叠加与演化对二道河银铅锌矿床的形成和富集具有非常重要的作用。;The Erdaohe silver-lead-zinc deposit is a newly discovered large skarn deposit in central Great Xing’an Range, and its formation is closely related to multi-stage intrusions. The ore bodies in the deposit mainly occur in skarns, marble, and fine-grained granodiorites. In this study, we conducted LA-ICP-MS zircon U-Pb dating, Hf isotopic analysis, and the electron microprobe analysis (EPMA) of garnets for the major intrusions and garnet granites in the deposit. Zircon grains from the epidotized fine-grained granodiorites, epidotized fine-grained diorites, and granite porphyry yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 506±4.3Ma, 213±2.8Ma, and 128±1.1Ma, respectively. The garnet skarns and epidote skarns in the Erdaohe deposit are frequently interspersed with each other, and the ore minerals such as sphalerite and galena in the deposit are characterized by recrystallization. Moreover, the EPMA results of garnets in the skarns show there were at least two stages of fluid activities with different natures. All these indicate that the Erdaohe deposit has undergone at least two stages of mineralization events. Zircons from three types of intrusions obtained yielded ε_Hf(t) values of 0.9~6.9, 8.3~15.1, and 7.9~14.1, respectively, with t_DM2 values of 1.6~1.1Ga, 0.8~0.3Ga, and 0.8~0.3Ga, respectively. This indicates that all these granitoids are originated from the partial melting of the juvenile crust, and their formation may be related to the combination of the Erguna and Xing’an blocks, the closure of the Mongol-Okhotsk Ocean, and the subduction of the Paleo-Pacific Plate, respectively. The superimposition and evolution of tectonic systems play a crucial role in the formation and enrichment of the Erdaohe silver-lead-zinc deposit.

Early Mesozoic subduction of the Mongol‐Okhotsk Ocean and its effect on the central Great Xing'an Range: Insights from the monzodiorite in the Erdaohe deposit

Stuck in the middle of the Mongol‐Okhotsk Ocean and the Palaeo‐Asian Ocean, the tectonic background of the Great Xing'an Range is ambiguous, especially with the tectonic transition in Early Mesozoic. Previous studies showed a major influence by the closure of the Palaeo‐Asian Ocean and the onset of the Mongol‐Okhotsk Ocean subduction on the southern and northern part of the Great Xing'an Range, respectively. However, the Early Mesozoic tectonic setting of the central Great Xing'an Range still needs further discussion. New zircon ages, whole‐rock geochemical data for monzodiorite in the Erdaohe deposit, central Great Xing'an Range, are presented. Zircon U–Pb dating yields a Triassic age of 226 Ma. Monzodiorite displays metaluminous and high‐K calc‐alkaline affinity evidenced by petrologic and geochemical studies. A mixed source of juvenile lower crust with mantle material of the monzodiorite is indicated by its high Mg# (44–61), low SiO2 (50–53 wt%) contents, depletion in Nb and Ta, positive εNd(t) (+2.5 ± 3.0) and zircon εHf(t) (+6.8 ± 8.9), and low ISr values (0.70322–0.70432). Our new geochronological and geochemical data with compiled data of previous research on magmatism from the Xing'an Block and adjacent areas indicate new insights into the Triassic tectonic evolution of the central Great Xing'an Range. The Triassic magmatism in this region is intimately associated with the flat‐slab subduction and slab break‐off of the Mongol‐Okhotsk Ocean.

Petrogenesis and tectonic implications of Late Mesozoic volcanic rocks in the northern and central Great Xing'an Range, NE China: Constraints from geochronology and geochemistry

In the northern and central Great Xing'an Range, there exist widespread Late Mesozoic volcanic rocks, of which the petrogenesis and geodynamic setting remain controversial. These rocks are composed of andesite, trachyandesite, basaltic andesite, and rhyolite. This study presents new data of zircon U–Pb dating, Hf isotopic composition, and whole‐rock geochemistry of the Late Jurassic intermediate‐mafic volcanic rocks within the northern Great Xing'an Range. In addition, the geochronological and geochemical data for the Late Mesozoic intermediate‐mafic rocks within the northern and central Great Xing'an Range are summarized for constraining the geochronological framework, petrogenesis, and geodynamic setting of the large‐scale Late Mesozoic volcanism in this region. The intermediate‐mafic volcanic rocks are enriched in large‐ion lithophiles and light rare earth elements and are depleted in high‐field‐strength elements such as Nb, Ta, and Ti, with positive εHf(t) values (+0.7 to +15.4). The data indicate that the volcanic rocks were derived from the partial melting of a mantle wedge that was modified by previously subducted slab‐derived fluids. These Late Mesozoic intermediate‐mafic volcanic rocks record a post‐collisional lithospheric extensional setting resulting from the closure of the Mongol‐Okhotsk Ocean.

Petrogenesis of highly differentiated I‐type volcanic rocks: Reinjection of high‐temperature magma—An example from Suolun silicic volcanic rocks, central Great Xing'an Range, China

Silicic volcanic rocks are the main components of the upper crust. Understanding their genesis can help us better understand the processes of crustal growth, reconstruction, and crust–mantle interactions. In this study, we examine silicic volcanic rocks from Suolun in the Great Xing'an Range, China. These silicic volcanic rocks are of Cretaceous age (140–123 Ma), with 68–76 wt% SiO2, and the majority are of the high‐K (calc‐alkaline) series. εHf(t) ranges between +1.7 and +9.9, mostly around 7. The Early Cretaceous silicic volcanic rocks from Suolun are cold‐wet‐oxidised, highly differentiated I‐type volcanic rocks, and plagioclase and K‐feldspar are the main fractionation phases. TTiZ shows that silicic magma undergoes a reheating process in the magma chamber, which causes the early rheological lock‐up magma to reactivate and thus drives it to further differentiation. This process is probably driven by the injection of high temperature magma at depth. The wet upwelling of the Mongol‐Okhotsk Oceanic plate in the deep resulted in large‐scale magmatism in the area. These results provide a possible explanation for the formation of highly differentiated magmatic rocks and further confirm the evolutionary link between volcanic rocks and plutonic systems.

Late Carboniferous mafic to felsic intrusive rocks in the central Great Xing’an Range, NE China: petrogenesis and tectonic implications

The timing of the amalgamation of the Xing’an and Songliao–Xilinhot blocks in the eastern Central Asian Orogenic Belt has long been the subject of debate. To explore this question, we studied a suite of late Carboniferous mafic to felsic intrusive rocks in the central Great Xing’an Range, NE China. These rocks yielded late Carboniferous zircon U–Pb isotopic ages of 320–300 Ma. The felsic monzogranites and granodiorites are strongly peraluminous with high A/CNK ratios (≥ 1.1), and they have signatures transitional between I- and S-type granites. Their geochemical characteristics suggest a magmatic source in a heterogeneous juvenile crust that included both clay-rich pelitic material and metabasalt. On the other hand, the intermediate biotite granodiorites have characteristics that suggest a dual magmatic source involving both mantle material and crustal contributions. The mafic gabbros were derived from the partial melting of mantle materials including both spinel and garnet lherzolite. The upwelling of the asthenospheric mantle contributed greatly to the formation of these magmas, with the upwelling as a result of the delamination of dense lithosphere and/or previously trapped mafic slabs. The petrology, geochemical signatures, field characteristics, and rock associations of the late Carboniferous mafic to felsic intrusive rocks imply that they formed in a post-collisional extensional tectonic setting that developed after the amalgamation of the Xing’an and Songliao–Xilinhot blocks and closure of the Nenjiang Ocean between them. Considering that the tectonic setting during the early Carboniferous was one of regional subduction, our data constrain the amalgamation of the Xing’an and Songliao–Xilinhot blocks and the closure of the Nenjiang Ocean to the early late Carboniferous.

Determination and geological implication of the Middle Jurassic post-collisional granitoids in Taerqi area, central Great Xing'an Range

Determination and geological implication of the Middle Jurassic post-collisional granitoids in Taerqi area, central Great Xing'an Range

Zircon and apatite as tools to monitor the evolution of fractionated I-type granites from the central Great Xing’an Range, NE China

It is widely accepted that granitic melts can be highly evolved, however, the effective records of this process are usually obscure, especially for the exsolution and evolution of volatiles. We present a comprehensive investigation on zircon and apatite from less to highly fractionated granites from the central Xing’an Range, NE China, in order to reveal the mineral records for the evolution processes of granitic melt. Petrographic, whole-rock and mineralogical geochemical investigations indicate that the three granites are co-magmatic and experienced different degrees of fractionation. The variations of zircon morphology, textures and geochemical compositions reflect the progressive evolution of granitic melts from volatile-undersaturated to oversaturated conditions. The significantly decreased Raman spectra intensities imply that the zircon crystals experienced increased radiation damages and hydrothermal alteration during the fractionation of granitic magma. Correspondingly, apatite textures transform from fluid-inclusion-free to fluid-inclusion-rich stage with increasing F/Cl ratios during the magmatic evolution, implying that the segregation of isolated fluid phase in the fractionating magma. Accordingly, we conclude that the textural and compositional evolution of zircon and apatite can be regarded as efficient tools for recording granitic magma evolution.

Geochemistry of Late Mesozoic volcanic rocks in the central Great Xing’an Range, NE China: petrogenesis and crustal growth in comparison with adjacent areas

ABSTRACTThe central Great Xing’an Range contains widespread exposures of Mesozoic igneous rocks, yet the origin of its Late Mesozoic volcanic rocks has long been controversial. They are composed of andesite, trachyte, trachyandesite, trachydacite, rhyolite, and minor basaltic andesite. The intermediate rocks are enriched in large ion lithophiles and light rare earth elements (LILEs and LREEs) and are depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti, with positive εHf(t) values (+6.2 to +13.4) and Hf single-stage model ages (TDM1 = 556–227 Ma). This indicates that they were derived from the partial melting of a mantle wedge that was modified by previously subducted slab-derived fluids was likely introduced with limited crustal contamination. The felsic rocks show positive εHf(t) values (+4.3 to +10.2) and Hf two-stage model ages (TDM2 = 910–544 Ma), with more enrichment of LILEs and LREEs and more depletion of HFSEs and negative Eu anomalies. This indicates that felsic rocks were mainly derived from partial melting of Neoproterozoic accreted quartz-amphibolite facies mafic crust. We summarise the geochronological and Hf-Nd isotope data for Mesozoic igneous rocks within the central Great Xing’an Range (CGXR), the northern Xing’an block (NXB), and the Erguna block (EB), with the aim of constraining the geochronological framework for Mesozoic volcanism and comparing the growth of continental crust. The evolution of Late Mesozoic magmatism in the three areas reached its climax ~125 Ma ago. Our data, together with regional isotope evidence, suggest that crustal accretion of the CGXR occurred during the Neoproterozoic–Phanerozoic. However, that of the EB occurred during the Meso- to Neoproterozoic. The EB exhibits more lateral and vertical heterogeneities and ancient continental crust than the CGXR and NXB in the northern magma source region.

Timing and evolution of Mesozoic volcanism in the central Great Xing'an Range, northeastern China

In this paper, we report on LA‐ICP‐MS zircon U–Pb dates of 14 Mesozoic volcanic rocks from the central Great Xing'an Range (CGXR). These data are integrated with the temporal and spatial distribution of local magmatism‐related Mesozoic mineralization, in an effort to develop an understanding of the geodynamic evolution of the region. Periodic magmatic events in the GXR date from ~1,703 through ~145 Ma. Mesozoic volcanism in the CGXR can be subdivided into three episodes: Triassic (250–205 Ma), Early–Middle Jurassic (182–165 Ma), and Late Jurassic–Early Cretaceous (155–115 Ma). A revision of the previously defined volcanic sequence is offered using a combination of our zircon U–Pb ages and published Mesozoic geological and geophysical evidence from northeast China. We propose that (a) Early–Middle Triassic volcanism in the CGXR resulted from subduction of the Paleo‐Asian oceanic plate; (b) Late Triassic volcanism was related to subduction of the Mongol–Okhotsk oceanic plate (especially near the Erguna Block) and subsequent extension after the closure of the Paleo‐Asian Ocean; (c) Early–Middle Jurassic volcanism was mainly controlled by the southward subduction of the Mongol–Okhotsk oceanic plate; (d) Late Jurassic–initial Early Cretaceous magmatism was initiated by closure of the Mongol–Okhotsk Ocean; and (e) late Early Cretaceous volcanism was induced following the final closure of the Mongol–Okhotsk Ocean and rollback of the Paleo‐Pacific oceanic plate.

Geochronology, petrogenesis, and tectonic implications of Permian felsic rocks of the Central Great Xing’an Range, NE China

The Hegenshan–Heihe Suture (HHS) is an important suture zone between the Xing’an and Songliao–Xilinhot blocks in the eastern Central Asian Orogenic Belt (CAOB). Many studies have examined the northern and southern parts of this suture zone, but the middle segment remains under-researched and controversial. This paper presents new research into Permian felsic rocks along the middle segment of the HHS, including alkaline granites, rhyolites, and granodiorites. Zircon U–Pb dating of these rocks yielded precise Permian ages of 300.4 ± 2.5, 292.8 ± 2.7, and 293.1 ± 2.2 Ma. The alkaline granites and the rhyolites are A-type rocks that were derived from lower crustal protoliths, with the melting of these protoliths caused by asthenospheric upwelling associated with lithospheric delamination. In comparison, the granodiorites are I-type granites were generated from a mantle-derived magmatic source. The petrogenesis of these granites also involved the assimilation of sedimentary rocks and fractional crystallization. This Permian magmatism occurred during post-collisional extension following the amalgamation of the Xing’an and Songliao–Xilinhot blocks.

Petrogenesis and metallogenesis of the Early Cretaceous Naoniushan Cu-dominated polymetallic deposit in the central Great Xing’an Range, NE China

The Naoniushan Cu-dominated polymetallic deposit in the central Great Xing’an Range is associated locally with Pb-Zn-Ag or Mo mineralization. Mineralization mainly occurs in the Lower Cretaceous continental volcanic rocks. Here, we present new LA-ICP-MS zircon U-Pb ages, whole-rock geochemical data, Sr-Nd-Hf isotopic data, and Re-Os ages for the Naoniushan deposit. The emplacement of the porphyry occurred at 137.8 ± 1.4 Ma and the mineralization at 134.3 ± 0.8 Ma. The granodiorite porphyry has high SiO2 (67.84–73.70 wt%) and K2O + Na2O (7.67–8.30 wt%) contents and low contents of MgO (0.60–1.04 wt%, Mg# = 0.44–0.51), TFeO (1.29–2.16 wt%), CaO (1.67–3.66 wt%) and K2O/Na2O (0.75–0.87). The porphyry is rich in large ion lithophile elements (LILEs, e.g., Rb, Sr, Ba, and K) and light rare earth elements (LREEs), without significant Eu anomalies (δEu = 0.84–1.01), and depleted in heavy REE (HREEs) with LREE/HREE = 12.78–16.57 and (La/Yb)N = 15.37–20.68, high field strength elements (HFSEs, e.g., Nb, Ta, and Ti) and siderophile elements (e.g., Cr, Co, and Ni). These features are similar to those of adakitic rocks derived from thickened lower crust. The Naoniushan porphyry exhibits positive εNd(t) values ranging from +1.9 to +2.8 and relatively low initial 87Sr/86Sr ratios, ranging from 0.70458 to 0.70497. Most in-situ zircon Hf isotopic analyses show variable positive εHf(t) values ranging from +3.1 to +9.4, corresponding to relatively young two-stage Hf model ages ranging from 994 to 591 Ma (excluding one spot). These isotopic features suggest that the primary magma of the Naoniushan granodiorite porphyry was mainly derived from the partial melting of Neoproterozoic juvenile lower crust (comprising a mixture of 80% juvenile basalt and 20% ancient lower crust). These elemental, isotopic, and geochronologic data, combined with the regional geology, deposit geology and fluid characteristics, suggest that the Naoniushan Cu-dominated polymetallic deposit formed in an evolving environment that decreased in compression over time due to slowing of the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate, and the transition from a compressional to an extensional tectonic regime following the closure of the Mongol-Okhotsk Ocean.

Geochronology, petrogenesis, and tectonic setting of Late Triassic volcanic rocks of the Hadataolegai Formation, central Great Xing'an Range, Northeast China

AbstractIn this study, new geochemical, zircon U–Pb, and Lu–Hf isotopic data are presented for volcanics from the Hadataolegai Formation of the central Great Xing'an Range (GXR) in Northeast China. These new data offer insights into the petrogenesis of the volcanics of the Hadataolegai Formation and the tectonic evolution of the Paleo–Asian Ocean (PAO) and Mongol–Okhotsk Ocean (MOO). These volcanics of the Hadataolegai Formation are divided into andesite‐trachyandesites and dacite‐trachydacites. Zircon U–Pb ages show that the volcanics of the Hadataolegai Formation erupted between 230 Ma and 228 Ma during the Late Triassic, which agrees with recently obtained data. The volcanic rocks in this study have low Y (9.9–21.1 ppm) and Yb (0.78–2.02 ppm) contents, high Sr (444–954 ppm) contents, and slight Eu anomalies (δEu = 0.82 to 0.94), similar to ‘adakite‐like’ rocks. The dacites were formed by fractional crystallization of coeval andesitic magmas. The zircons within the andesite and trachyandesite yield higher positive εHf(t) values (+6.3 to +12.0) and model ages (TDM2) between 860 Ma and 453 Ma, which indicates that the magmas were generated by a newly accreted continental crustal source. Moreover, some of the volcanics are relatively high in MgO contents. These characteristics indicate that the volcanic magmas were derived from the partial melting of delaminated lower crust and mixing with mantle materials. Combining these data with previous studies, we suggest that the magmatism in the central GXR was governed by extension due to the closure of the PAO and the back‐arc extension associated with the southward subduction of the MOO plate (western GXR, near the Erguna Block).