Spatial-temporal distribution and geochemistry of highly evolved Mesozoic granites in Great Xing’an Range,NE China:Discriminant criteria and geological significance

Highly evolved granite is an important sign of the mature continent crust and closely associated with deposits of rare metals.In this work,the authors undertake systematically zircon U-Pb ages and whole rock elemental data for highly evolved granitic intrusions from the Great Xing’an Range(GXR),NE China,to elucidate their discriminant criteria,spatial-temporal distribution,differentiation and geodynamic mecha-nism.Geochemical data of these highly evolved granites suggest that high w(SiO_(2))(>70%)and differentiation index(DI>88)could be quantified indicators,while strong Eu depletion,high TE_(1,3),lowΣREE and low Zr/Hf,Nb/Ta,K/Rb could only be qualitative indicators.Zircon U-Pb ages suggest that the highly evolved gran-ites in the GXR were mainly formed in Late Mesozoic,which can be divided into two major stages:Late Ju-rassic-early Early Cretaceous(162-136 Ma,peak at 138 Ma),and late Early Cretaceous(136-106 Ma,peak at 126 Ma).The highly evolved granites are mainly distributed in the central-southern GXR,and display a weakly trend of getting younger from northwest to southeast,meanwhile indicating the metallogenic potential of rare metals within the central GXR.The spatial-temporal distribution,combined with regional geological data,indicates the highly evolved Mesozoic granites in the GXR were emplaced in an extensional environ-ment,of which the Late Jurassic-early Early Cretaceous extension was related to the closure of the Mongol-Okhotsk Ocean and roll-back of the Paleo-Pacific Plate,while the late Early Cretaceous extension was mainly related to the roll-back of the Paleo-Pacific Plate.

Zircon U-Pb geochronology,geochemistry and tectonic implication of volcanic rocks from Manketouebo Formation in Keyihe area of northern Great Xing'an Range

Zircon U-Pb isotope dating and whole-rock geochemical analyses were undertaken for the rhyolite,rhyolitic lithic crystal tuff and dacitic tuff from the Manketouebo Formation in the Keyihe area,in order to constrain their genesis and tectonic significance.Zircon LA-ICP-MS U-Pb data indicate that the rhyolite and rhyolitic lithic crystal tuff were formed during 137±5 Ma and 143±1 Ma,respectively.These volcanic rocks have high SiO2(70.03%–76.46%)and K2O+Na2O(8.10%–9.52%)contents,but low CaO(0.03%–0.95%)and MgO(0.07%–0.67%)contents,which belong to the peraluminous and high-K calc-alkaline rocks.They are enriched in light rare earth elements(REEs),and exhibit fractionation of light over heavy REEs,withδEu values of 0.37–0.83.The volcanic rocks are enriched in LILEs(e.g.,Rb,U and K)and depleted in HFSEs(e.g.,Nb,Ti,P and Ta).The chemical composition suggests that these volcanic rocks formed by partial melting of crust material.Combined with previous regional research results,the authors consider that the volcanic rocks of the Manketouebo Formation in the Keyihe area were formed under an extensional environment related to the closure of the Mongolia–Okhotsk Ocean.

Geochemical Characteristics and Geological Significance of Early Permian Baya'ertuhushuo Gabbro in South Great Xing'an Range

Field geological investigation and geochemical analysis are carried out on Baya＇ertuhushuo Gabbro in South Great Xing＇an Range. Field investigation reveals that the gabbro is a magmatic intrusion rather than a component of an ophiolite suite as previously thought. Zircon laser ablation inductively coupled plasma mass spectroscopy （LA-ICP-MS） U-Pb dating indicates the gabbro was formed in 274-275 Ma, just as the widespread volcanic rocks of Dashizhai Formation （P1d）, monzogranites and miarolitic alkali-feldspar granites in the study area. The gabbro has SiO2 content between 47.23 wt% and 50.17 wt%, high MgO and FeOT contents of 6.95-11.29 wt% and 7.32- 12.24wt%, respectively, and it belongs to low-K tholeiitic series in the SiO2-K2O diagram. The Chondrite-normalized rare earth element （REE） patterns and primitive mantle-normalized spider diagrams of the gabbro are similar to those of Normal Mid-Ocean Ridge Basalt （N-MORB） except for the enrichment of large ion lithophfle elements （LILE）, such as Rb, Ba and K. In trace element tectonic discriminative diagrams, the samples are mainly plotted in the N-MORB field, and Zircon in situ Lu-Hf isotopic analysis also indicates the gabbro originated from depleted mantle. Through synthetic studies of the geochemical characteristics and petrogenesis of Baya＇ertuhushuo gabbro, volcanic rocks of Dashizhai Formation and granitoids in the area, it is suggested that the early Permian magmatism in the Xilinhot-Xiwuqi area formed in the tectonic setting of asthenosphere upwelling, which was caused by breaking-off of the subducted Paleo-Asian Ocean slab.

Felsic Igneous Rocks in the Hua'aobaote Pb-Zn-Ag Polymetallic Orefield,Southern Great Xing'an Range:Genesis,Metallogenetic and Tectonic Significance

The Hua’aobaote Pb-Zn-Ag Polymetallic orefield is situated in the southern section of the Great Xing’an Range(GXAR),which has experienced extensive magmatism.Since the Paleozoic,there are two stages of magmatism in Hua’aobaote orefield occurred in the Paleozoic and Mesozoic.The Mesozoic magmatism is of great significance for the PbZn-Ag Polymetallic mineralization in Hua’aobaote orefield.In this study,new geochemical data was obtained to discuss the timing and petrogenesis of the magmatic rocks and its geodynamic and metallogenic significance.Zircon U-Pb ages reveal that the felsic igneous rocks from the Hua’aobaote orefield were formed in the Early Permian(294.8±3.2 Ma)and Early Cretaceous(132.6±1.4 Ma).Geochemically,the Early Permian granodiorite porphyrite is characterized by high Sr/Y(42-63)ratios and Mg^(#)(62.24-70.74)values and low heavy rare earth element(HREE)(5.09-6.79 ppm)contents.The granodiorite porphyrite is also characterized by depleted Sr-Nd initial isotopic signatures[ε_(Nd)(t)=5.91-7.59,(^(87)Sr/^(86)Sr)i=0.7029-0.7030],exhibiting adakitic characteristics.The Early Cretaceous granite porphyry and rhyolite are A-type felsic igneous rocks,and demonstrate high SiO_(2),Na_(2)O+K_(2)O and rare earth element(REE)contents,low CaO and MgO contents,low(^(87)Sr/^(86)Sr)i ratios(0.7044-0.7058),and positive ε_(Nd)(t)values(2.57-4.65).Whole-rock Pb isotopic compositions in granodiorite porphyrite are:206Pb/204Pb=17.631-18.149,^(207)Pb/^(204)Pb=15.422-15.450,and ^(208)Pb/^(204)Pb=37.325-37.729.The granite porphyry and rhyolite have initial ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb,and ^(208)Pb/^(204)Pb ratios of 18.106-19.309,15.489-15.539,and 37.821-38.05,respectively.Sr-Nd-Pb isotopic evidence suggests that the Early Permian granodiorite porphyrite is likely to derive from slab melts and modified by peridotitic mantle wedge in the subduction tectonic setting of the Paleo-Asian Ocean.The Early Cretaceous A-type felsic igneous rocks were derived from juvenile lower crust,accompanied by limited crustal contamination and various degree of fractional crystallisation during magma emplacement.The Early Cretaceous magmatism and related mineralization were formed in a post-orogenic tectonic setting that attributed to the closure of the Mongol-Okhotsk Ocean.Pb isotopic data for the various rock units in the study area indicate that the Mesozoic magma source contributed substantial Pb,Zn,and Ag to the Hua’aobaote deposit.

New Discovery of the Late Triassic Terrigenous Sediments in the Great Xing＇＇an Range Region,NE China and its Geological Significance

Objective The Great Xing＇an Range is located in the eastern section of Central Asian Orogenic Belt（CAOB）.As a superposed position of multiple tectonic domains,its structural evoIlution has always been a focused issue of geological research.

Magmatic Evolution and Mineralization Process of the Super-Large Shihuiyao Rb–Nb–Ta Deposit,Southern Great Xing'an Range,China

Rare metal ore reserves are an important strategic resource, and their metallogenic mechanism and mineralization studies have also been received widespread international attention.

Geochronology,Fluid Inclusions and Isotopic Characteristics of the Dongjun Pb-Zn-Ag Deposit,Inner Mongolia,NE China

The Dongjun Pb-Zn-Ag deposit in the northern part of the Great Xing’an Range(NE China)consists of quartzsulfide vein-type and breccia-type mineralization,related to granite porphyry.Hydrothermal alteration is well-developed and includes potassic-silicic-sericitic alteration,phyllic alteration and propylitic alteration.Three stages of mineralization are recognized on the basis of field evidence and petrographic observation,demarcated by assemblages of quartz-pyritearsenopyrite(early stage),quartz-polymetallic sulfide(intermediate stage)and quartz-carbonate-pyrite(late stage).Zircon LA-ICP-MS U-Pb dating indicates that the granite porphyry was emplaced at 146.7±1.2 Ma(Late Jurassic).Microthermometry and laser Raman spectroscopy shows that ore minerals were deposited in conditions of intermediate temperatures(175-359℃),low salinity(0.5-9.3 wt% Na Cl eqv.)and low density(0.60-0.91 g/cm^(3)).Ore-forming fluids were derived largely from magmatic hydrothermal processes,with late-stage addition of meteoric water,belonging to a H_(2)O-NaCl-CO_(2)±CH_(4) system.The δ^(34)SV-CDT values range from 0.75‰ to 4.70‰.The ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb,and ^(208)Pb/^(204)Pb values of the ore minerals are in the ranges of 18.240-18.371,15.542-15.570,and 38.100-38.178,respectively.Data for the S and Pb isotopic systems indicate that the ore-forming metals and sulfur were derived from Mesozoic magma.Based on the geological characteristics and geochemical signatures documented in this study,we conclude that the Dongjun deposit is a mesothermal magmatic hydrothermal vein-type Pb-Zn-Ag deposit controlled by fractures and related to granite porphyry,in response to Late Jurassic tectonic-magmatic-hydrothermal activity.We further conclude that fluid immiscibility,fluid mixing and fluid-rock interactions were the dominant mechanisms for deposition of the ore-forming materials.

Late Mesozoic Tectono-Thermal History in the South Margin of Great Xing’an Range,NE China:Insights from Zircon and Apatite(U-Th)/He Ages

The Late Mesozoic tectono-thermal evolution and geodynamic setting of the Great Xing’an Range(GXR),particularly in the south margin,are still ambiguous.In this study,we present original low-temperature thermochronological data of six granitoid samples collected from Maanzi pluton in the south margin of the GXR.The apatite and zircon(U-Th)/He ages vary of 70.8 ± 4.3-119.0 ±7.0 Ma and 120.0 ± 7.1-146.7 ± 8.7 Ma,respectively.Further numerical inverse modeling results reveal that the granitoid plutons experienced a rapid cooling and exhumation stage during Early Cretaceous with a rate of ~5.0-6.0 ℃/Ma and ~0.14-0.17 mm/yr,respectively,including the western minor pluton emplaced during Early Permian and the major pluton crystallized in latest Jurassic,corresponding to the extensional tectonics in NE China.The rapid exhumation processes in the south margin of the GXR during the Early Cretaceous could be related to both the rollback of Paleo-Pacific oceanic plate and the collapse of thickened crust in the Mongol-Okhotsk Orogen.

Fluid inclusions,C-H-O-S-Pb isotope systematics,geochronology and geochemistry of the Budunhua Cu deposit,northeast China:Implications for ore genesis

The Budunhua Cu deposit is located in the Tuquan ore-concentrated area of the southern Great Xing’an Range,NE China.This deposit includes the southern Jinjiling and northern Kongqueshan ore blocks,separated by the Budunhua granitic pluton.Cu mineralization occurs mainly as stockworks or veins in the outer contact zone between tonalite porphyry and Permian metasandstone.The ore-forming process can be divided into four stages involving stage Ⅰ quartz-pyrite-arsenopyrite;stage Ⅱ quartz-pyrite-chalcopyrite-pyrrhotite;stage Ⅲ quartz--polynetallic sulfides;and stage IV quartz-calcite.Three types of fluid inclusions(FIs) can be distinguished in the Budunhua deposit:liquid-rich two-phase aqueous FIs(L-type),vapour-rich aqueous FIs(V-type),and daughter mineral-bearing multi-phase FIs(S-type).Quartz of stages Ⅰ-Ⅲ contains all types of FIs,whereas only L-type FIs are evident in stage Ⅳ veins.The coexisting V-and S-type FIs of stages Ⅰ-Ⅲ have similar homogenization temperatures but contrasting salinities,which indicates that fluid boiling occurred.The FIs of stages Ⅰ,Ⅱ,Ⅲ,and Ⅳyield homogenization temperatures of 265-396℃,245-350℃,200-300℃,and 90-228℃ with salinities of3.4-44.3 wt.%,2.9-40.2 wt.%,1.4-38.2 wt.%,and 0.9-9.2 wt.% NaCl eqv.,respectively.Ore-forming fluids of the Budunhua deposit are characterized by high temperatures,moderate salinities,and relatively oxidizing conditions typical of an H2 O-NaCl fluid system.Mineralization in the Budunhua deposit occurred at a depth of0.3-1.5 km,with fluid boiling and mixing likely being responsible for ore precipitation.C-H-O-S-Pb isotope studies indicate a predominantly magmatic origin for the ore-forming fluids and materials.LA-ICP-MS zircon U-Pb analyses indicate that ore-forming tonalite porphyry and post-ore dioritic porphyrite were formed at 151.1±1.1 Ma and 129.9±1.9 Ma,respectively.Geochemical data imply that the primary magma of the tonalite porphyry formed through partial melting of Neoproterozoic lower crust.On the basis of available evidence,we suggest that the Budunhua deposit is a porphyry ore system that is spatially,temporally,and genetically associated with tonalite porphyry and formed in a post-collision extensional setting following closure of the Mongol-Okhotsk Ocean.

Late Jurassic adakitic ore-bearing granodiorite porphyry intrusions in the Xiaokele porphyry Cu(–Mo)deposit,Northeast China:implications for petrogenesis and tectonic setting

The Xiaokele Cu(–Mo)deposit is a recently discovered porphyry deposit in the northern Great Xing’an Range(GXR)of northeast China.The ore bodies in this deposit are mainly hosted within granodiorite porphyry intrusions.Potassic,phyllic,and propylitic alteration zones develop from center to edge.In this paper,we present zircon LA–ICP–MS U–Pb ages,zircon Hf isotopic compositions,and whole-rock geochemistry of the ore-bearing granodiorite porphyries from the Xiaokele Cu(–Mo)deposit.Zircon U–Pb dating suggests that the Xiaokele granodiorite porphyries were emplaced at 148.8±1.1 Ma(weighted-mean age;n=14).The Xiaokele granodiorite porphyries display high SiO2,Al2O3,Sr,and Sr/Y,low K2O/Na2O,MgO,Yb,and Y,belonging to high-SiO2 adakites produced by partial melting of the subducted oceanic slab.Marine sediments were involved in the magma source of the Xiaokele granodiorite porphyries,as indicated by enriched Sr–Nd isotopic compositions(eNd(-t)=-1.17–-0.27),low positive zircon eHf(t)values(0.4–2.2),and high Th contents(4.06–5.20).The adakitic magma subsequently interacted with the mantle peridotites during ascent through the mantle wedge.The Xiaokele granodiorite porphyries were derived from slab melting during the southward subduction of the Mongol–Okhotsk Ocean.

Timing of the formation of the Baiyinnuo'er skarn Zn–Pb deposit,NE China:evidence from sulfide Rb–Sr dating

The Baiyinnuo’er deposit in northern China is located in the south section of the Great Xing’an Range,and it is the largest skarn Zn–Pb deposit in the region.Skarn and Zn–Pb orebodies mainly occur between the different units of the Permian Huanggangliang Formation,or within the contact zone between the intrusive rocks and the marble.Although Baiyinnuo’er has been well investigated previously,the timing of the Zn–Pb mineralization is still controversial,largely due to the lack of appropriate ore or alteration minerals that could be directly used for isotopic dating.In this study,we report the results of Rb–Sr isotopic analysis for sphalerite and pyrite samples from the Baiyinnuo’er orebodies,which yielded two isochron ages of 137.4±3.4 and 140.0±7.8 Ma,respectively,constraining the Zn–Pb mineralization time of the deposit as the Early Cretaceous.The data are also consistent with the age of the granitoids in the mining area,indicating a potential genetic relationship between the Early Cretaceous magmatism and mineralization.Many other intrusion-related hydrothermal deposits(including the two typical skarns,Huanggang and Haobugao)in the southern Great Xing’an Range also share similar mineralization ages(i.e.,140–130 Ma).Together,these data suggest an Early Cretaceous mineralization event in this region,and this largescale mineralization could be related to the regional tectonic regime transition from compression to extension as a result of the rollback of the subducted Paleo-Pacific plate.The initial87 Sr/86 Sr ratios of the sphalerite and pyrite samples are 0.70569 and 0.70616,respectively,implying that the ore-forming material could have a significant contribution from the mantle components.The current study shows that sulfide Rb–Sr dating could be used in deciphering the timing of skarn deposit formation.