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1.
The Shuangqing Fe–Pb–Zn–Cu deposit is located in the Xiangride County of Qinghai Province, China, and is a typical example of skarn deposits in the East Kunlun Mountains. Skarnization and mineralization took place along the contact zone between Carboniferous carbonates and the concealed Triassic plagiogranite. LA–ICP–MS U–Pb dating of zircons from the plagiogranite has yielded ages of 227.2 ± 1.0 and 226.54 ± 0.97 Ma, which are interpreted as the emplacement age of the plagiogranite. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 226.5 ± 5.1 Ma. These age data confirm that both intrusion and related skarn mineralization initiated at ~ 227 Ma. Re contents of molybdenite, zircon εHf(t) and 176Hf/177Hf values fall into the ranges 3.31 to 6.58 μg/g, − 8.6 to − 0.0, and 0.282403 to 0.28263850, respectively. The timing of the Shuangqing Fe–Pb–Zn–Cu mineralization coincided with a major change in the stress field in East Kunlun from transpression to extension, related to the partial melting of thickening crustal materials in a post-collisional tectonic setting. 相似文献
2.
The northeastern Gangdese Pb–Zn–Ag–Fe–Mo–W polymetallic belt (NGPB), characterized by skarn and porphyry deposits, is one of the most important metallogenic belts in the Himalaya–Tibetan continental orogenic system. This belt extends for nearly four hundred kilometers along the Luobadui–Milashan Fault in the central Lhasa subterrane, and contains more than 10 large ore deposits with high potential for development. Three major types of mineralization system have been identified: skarn Fe systems, skarn/breccia Pb–Zn–Ag systems, and porphyry/skarn Mo–Cu–W systems. In this study, we conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf isotopic study of ore-forming rocks in the NGPB, specifically the Jiangga, Jiaduopule, and Rema skarn Fe deposits, and the Yaguila Pb–Zn–Ag deposit. Although some of these deposits (porphyry Mo systems) formed during the post-collisional stage (21–14 Ma), the majority (these three systems) developed during the main (‘soft collision’) stage of the India–Asia continental collision (65–50 Ma). The skarn Fe deposits are commonly associated with granodiorites, monzogranites, and granites, and formed between 65 and 50 Ma. The ore-forming intrusions of the Pb–Zn–Ag deposits are characterized by granite, quartz porphyry, and granite porphyry, which developed in the interval of 65–55 Ma. The ore-forming porphyries in the Sharang Mo deposit, formed at 53 Ma. The rocks from Fe deposits are metaluminous, and have relatively lower SiO2, and higher CaO, MgO, FeO contents than the intrusions associated with Mo and Pb–Zn–Ag mineralization, while the Pb–Zn–Ag deposits are peraluminous, and have high SiO2 and high total alkali concentrations. They all exhibit moderately fractionated REE patterns characterized by lower contents of heavy REE relative to light REE, and they are enriched in large-ion lithophile elements and relatively depleted in high-field-strength elements. Ore-forming granites from Fe deposits display 87Sr/86Sr(i) = 0.7054–0.7074 and εNd(t) = − 4.7 to + 1.3, whereas rocks from the Yaguila Pb–Zn–Ag deposit have 87Sr/86Sr(i) = 0.7266–0.7281 and εNd(t) = − 13.5 to − 13.3. In situ Lu–Hf isotopic analyses of zircons from Fe deposits show that εHf(t) values range from − 7.3 to + 6.6, with TDM(Hf)C model ages of 712 to 1589 Ma, and Yaguila Pb–Zn–Ag deposit has εHf(t) values from − 13.9 to − 1.3 with TDM(Hf)C model ages of 1216 to 2016 Ma. Combined with existing data from the Sharang Mo deposit, we conclude that the ore-forming intrusions associated with the skarn Fe and porphyry Mo deposits were derived from partial melting of metasomatized lithospheric mantle and rejuvenated lower crust beneath the central Lhasa subterrane, respectively. Melting of the ancient continental material was critical for the development of the Pb–Zn–Ag system. Therefore, it is likely that the source rocks play an important role in determining the metal endowment of intrusions formed during the initial stage of the India–Asia continental collision. 相似文献
3.
Crustal xenoliths can provide new insights into the unexposed crust, and those from the northeastern Yangtze Block have rarely been studied. This paper reports U–Pb–Hf isotopes and trace-element compositions of zircons from six felsic xenoliths hosted by the Neogene alkali basalts in the Donghai region (i.e. Anfengshan and Pingmingshan) of the Sulu orogen in central eastern China. The xenoliths are mainly composed of orthoclase and quartz, or orthoclase and natrolite, with accessory minerals of Fe–Ti oxides and zircon. Most zircon grains show core-rim structures, with the cores and rims being magmatic and metamorphic in origin, respectively. The zircon cores mainly yield ages of ca. 827–794 Ma, while the zircon rims give ages of ca. 232–212 Ma. We interpret the zircon core ages as the time of an early Mid-Neoproterozoic magmatic event in the northeastern Yangtze Block and the zircon rim ages as the time of collision between the Yangtze and North China Blocks. Our data suggest that much more ca. 830–800 Ma magmatic records are possibly preserved in the unexposed deep crust, and the early Mid-Neoproterozoic is an important era for the crust evolution of the northeastern Yangtze Block. The new zircon Hf isotopic analyses show that the Anfengshan sample (south of Donghai) has zircon εHf (820 Ma) values ranging from −15.3 to −9.4, and two-stage Hf model ages of 2.66–2.30 Ga; the Pingmingshan sample (southeast of Donghai) has zircon εHf (820 Ma) values ranging from −1.4 to +3.8, and two-stage Hf model ages of 1.80–1.47 Ga. These data suggest that ancient crust as old as Neoarchean to Mesoproterozoic was involved in the early Mid-Neoproterozoic magmatism. Combined with the previously reported zircon U–Pb–Hf results of the exposed rocks, it is highlighted that crustal recycling was dominant in the early Mid-Neoproterozoic (ca. 830–800 Ma) magmatism, whereas both crustal recycling and addition of mantle-derived melts were significant in the late Mid-Neoproterozoic (ca. 800–720 Ma) magmatism in the northeastern Yangtze Block. 相似文献
4.
The recently discovered Longtougang skarn and hydrothermal vein Cu–Zn deposit is located in the North Wuyi area, southeastern China. The intrusions in the ore district comprise several small porphyritic biotite monzonite, porphyritic monzonite, and porphyritic granite plutons and dikes. The mineralization is zoned from a lower zone of Cu-rich veins and Cu–Zn skarns to an upper zone of banded Zn–Pb mineralization in massive epidote altered rocks. The deposit is associated with skarn, potassic, epidote, greisen, siliceous, and carbonate alteration. Molybdenite from the Cu-rich veins yielded a Re–Os isochron age of 153.6 ± 3.9 Ma, which is consistent with U–Pb zircon ages of 154.0 ± 1.3 Ma for porphyritic monzonite, 154.0 ± 0.8 Ma for porphyritic biotite monzonite, and 152.0 ± 0.8 Ma for porphyritic granite. Geological observations suggest that the Cu mineralization is genetically related to the porphyritic biotite monzonite and porphyritic monzonite. All the zircons from intrusive rocks in the ore district are characterized by εHf(t) values between − 13.41 and − 4.38 and Hf model ages (TDM2) between 2054 and 1482 Ma, reflecting magmas derived mainly from a Proterozoic crustal source. Molybdenite grains from the deposit have Re values of 14.6–27.7 ppm, indicative of a mixed mantle–crust source. The porphyry–skarn abundant Cu and hydrothermal vein type Pb–Zn–Ag deposits in the North Wuyi area are related to the Late Jurassic porphyritic granites and Early Cretaceous volcanism, respectively. The Late Jurassic mineralization-related granites were derived from the crustal anatexis with some mantle input, which was triggered by asthenospheric upwelling induced by slab tearing during oblique subduction of the paleo-Pacific plate beneath the South China block, and the Early Cretaceous mineralization-related granitoids mainly from crust material formed within a series of NNE-trending basins during margin-parallel movement of the plate. 相似文献
5.
The Taoxihu deposit (eastern Guangdong, SE China) is a newly discovered Sn polymetallic deposit. Zircon U-Pb dating yielded 141.8 ± 1.0 Ma for the Sn-bearing granite porphyry and 145.5 ± 1.6 Ma for the biotite granite batholith it intruded. The age of the granite porphyry is consistent (within error) with the molybdenite Re–Os isochron age (139.0 ± 1.1 Ma) of the Sn mineralization, indicating a temporal link between the two. Geochemical data show that the granite porphyry is weakly peraluminous, contain high Si, Na and K, low Fe, Mg, Ca and P, and relatively high Rb/Sr and low K/Rb values. The rocks are enriched in Rb, Th, U, K, and Pb and depleted in Ba, Sr, Ti and Eu, resembling highly fractionated I-type granites. They contain bulk rock initial 87Sr/87Sr of 0.707371–0.707730 and εNd(t) of −5.17 to −4.67, and zircon εHf(t) values from −6.67 to −2.32, with late Mesoproterozoic TDM2 ages for both Nd and Hf isotopes. This suggests that the granite porphyry was likely formed by the partial melting of the crustal basement of Mesoproterozoic overall residence age with minor mantle input.δ34SCDT values of the Taoxihu chalcopyrite and pyrite range from 0.1 to 2.1‰ (average: 0.9‰), implying a dominantly magmatic sulfur source. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the Taoxihu sulfide ores are 18.497–18.669, 15.642–15.673 and 38.764–38.934, respectively, indicating a mainly upper continental crustal lead source with minor mantle contribution. The highly fractionated and reduced (low calculated zircon Ce4+/Ce3+ and EuN/EuN1 values) nature of the ore-forming granitic magma may have facilitated the Sn enrichment and played a key role in the Sn mineralization. We propose that the ore-forming fluids at Taoxihu were of magmatic-hydrothermal origin derived from the granite porphyry, and that both the granite porphyry and the Sn mineralization were likely formed in an extensional setting, possibly related to the subduction slab rollback of the Paleo-Pacific Plate. 相似文献
6.
The Sri Lankan fragment of Gondwana preserves the records of Neoproterozoic tectonothermal events associated with the final assembly of the supercontinent. Here we investigate a suite of magmatic rocks from the Wanni, Kadugannawa and Highland Complexes through geological, petrological, geochemical and zircon U–Pb and Lu–Hf isotopic techniques. The hornblende biotite gneiss, charnockites, metagabbro and metadiorites investigated in this study show geochemical features consistent with calc-alkaline affinity and subduction-related signature including LILE enrichment relative to HFSE coupled with distinct Nb–Ta depletion and weak negative Zr–Hf anomalies. The felsic suite falls in the volcanic arc granites (VAGs) field and the mafic suite shows island arc basalt affinity in tectonic discrimination plots, suggesting that the protoliths of the rocks were derived from arc-related magmas in a convergent margin setting. LA-ICPMS zircon U–Pb analyses show crystallization of charnockite and dioritic mafic magmatic enclave from the Highland Complex during ca. 565 and 576 Ma corresponding to bimodal magmatism. The diorite also contains metamorphic zircons of ca. 525 Ma. Hornblende–biotite gneiss from the Kadugannawa Complex shows protolith emplacement age at 973–980 Ma, followed by new zircon growth during repeated thermal events through late Neoproterozoic. The dioritic enclaves in these rocks are much younger, and form part of a deformed and metamorphosed dyke suite with emplacement ages of 559 Ma, broadly coeval with the bimodal magmatism in the Highland Complex at that time. The youngest group of zircons in this rock shows ages of 508 Ma, corresponding to the latest thermal event. A charnockite from this locality shows oldest group of zircons at 962 Ma, corresponding to emplacement age similar to that of the magmatic protolith of the hornblende biotite gneiss. This rock also shows zircon growth during repeated thermal events at 832 Ma, 780 Ma, 721 Ma and 661–605 Ma. The lower intercept age of 543 Ma marks the timing of collisional metamorphism. Charnockite from the Wanni Complex shows emplacement age at 1000 Ma, followed by thermal event at 570 Ma, the latter correlating with the bimodal magmatic event in the Highland Complex. The dioritic enclave within this charnockite shows an age of ca. 980 Ma, suggesting intrusion of mafic magma into the felsic magma chamber. Zircons in the diorite also record multiple zircon events during 950 to 750 Ma. Zircons in the Highland Complex charnockite possess negative εHf(t) values in the range − 6.7 to − 12.6 with TDMC of 2039–2306 Ma suggesting magma derivation through melting of Paleoproterozoic source. In contrast, the εHf(t) range of − 11.1 to 1.6 suggests a mixed source of both of older crustal and juvenile material. The εHf(t) values of − 4.5 to 4.5 and TDMC of 1546–1962 Ma for the hornblende biotite gneiss also shows magma derivation from mixed sources that included Paleoproterozoic components. The younger dioritic intrusive, however, has a more juvenile magma source as indicated by the mean εHf(t) value of 1.3. The associated charnockite shows a tight positive cluster of εHf(t) from 0.6 to 5.1, suggesting juvenile input. Charnockite from the Wanni Complex shows clearly positive εHf(t) values of up to 13.1, and TDMC in the range 937–1458 Ma suggesting much younger and depleted mantle source. The diorite enclave also has positive εHf(t) values with an average value of 8.5 and TDMC in the range of 709–1443 Ma clearly suggesting younger juvenile sources. The early and late Neoproterozoic bimodal suites are correlated to convergent margin magmatism associated with the assembly of Sri Lanka within the Gondwana supercontinent. 相似文献
7.
Extensive Early Cretaceous post-collisional igneous rocks, especially the large volume of granitoids developed in the Dabie orogen. Some of these granitic rocks are spatially, temporally, and genetically associated with economically important molybdenum deposits. The Tangjiaping large-scale (> 0.1 million ton) porphyry Mo deposit is located in the northwest of the Northern Dabie Complex unit. The Mo mineralization is mainly hosted in molybdenite-bearing quartz veinlets and stockworks in the Tangjiaping granite porphyry, which intruded into Proterozoic biotite-plagioclase gneiss and amphibole-plagioclase gneiss. Two alteration zones from the porphyry centre outwards and downwards can be recognized: (1) K-silicate alteration-silicification zone; (2) silicification-phyllic alteration zone. The Tangjiaping ore-bearing granite porphyry occurs as an individual stock with an outcrop of 0.4 km2. LA-ICP-MS zircon U-Pb dating of the Tangjiaping granite porphyry yields crystallization age of 115 ± 1 Ma, which is consistent with the molybdenite Re-Os age of the deposit given by previous studies. The Tangjiaping granitic rocks are metaluminous and belong to high-K calc-alkaline and shoshonitic series. They are relatively enriched in light rare earth elements and have moderately negative Eu anomalies. Geochemical and mineralogical characteristics indicate that the Tangjiaping granite is an A-type granite and was generated by partial melting of intermediate-felsic rocks at pressures of ca. 0.4–0.8 GPa. There are high initial 87Sr/86Sr ratios ranging from 0.707367 to 0.709410 and negative εNd(t) values varying from − 15.0 to − 14.2 for the Tangjiaping granite. In situ zircon Hf isotopic analyses show that the εHf(t) values of zircons from the Tangjiaping granite porphyry vary from − 17.0 to − 6.0. The geochemical data and Sr-Nd-Hf isotopes, coupled with the Neoproterozoic inherited zircon age (652 ± 21 Ma), indicate that the Tangjiaping granite porphyry was most likely derived from partial melting of the Northern Dabie gneiss with some relatively enriched mantle materials involved. The Tangjiaping Mo ore-forming granite porphyry was formed in an extensional setting. The Early Cretaceous asthenospheric upwelling might have played an important role in the formation of the approximately coeval Mo-bearing magmas in the Dabie orogen. 相似文献
8.
The Dongping gold deposit, located in Chongli County (Hebei Province) about 200 km northwest of Beijing, is one of the largest gold-producing areas along the northern margin of the North China Craton. It is located in the of Shuiquangou alkaline igneous complex of Middle Devonian age (394.3 ± 3.2 Ma), composed chiefly of highly alkaline syentite and quartz syenites. This study reveals the age of the Carboniferous in the deposit at 351.7 ± 2.8 Ma (MSWD = 1.9). The Dongping deposit is locally hosted in Cretaceous (~143 ± 1 Ma) alkali granites that intruded the older and the gold mineralization is closely associated genetically with this event. Hydrothermal zircons in the alkali granites have Th/U ratios mostly ranging between 0.01 and 0.7 indicating oscillatory zoning. A few grains with high Th/U ratios (1.31–2.07) may be from metamorphic domains. Negative εHf(t) values of the zircon mainly range between −19.75 and −16.93, suggesting that they originated principally by the melting of recycled continental crust. Less abundant zircons with εHf(t) ranging from −25.76 to −23.46, with Hf model ages (TDM2) of 2.54 to 2.67 Ga, (mainly 2.2 to 2.3 Ga) suggest that recycled Neoarchean basement was also present in the source region. The Devonian syenites and quartz syenites have TDM1 ages ranging from 1.96 to 2.08 Ga. Zircons from these rocks have εHf(t) values of −11.9 to −18.9. Certain zircons from the gold-bearing granite of Paleozoic age have an initial 176Hf/177Hf ratio of 0.281816 to 0.282058 and 0.282147 to 0.282348, reflecting a homogenous distribution of hafnium isotopes typical of magmatic sources. The TDM1 and TDM2 of the latest intrusion varying 1.33 to 1.59 Ga and 1.72 to 2.11 Ga respectively, indicating that the Neoproterozoic to Mesoproterozoic rocks of this area are an important source for the younger magma which are important to forming ore deposits. The TDM2 indicate that the magma may be derived from a very old crustal basement (~2.67 Ga) in the northern margin of North China Craton by partial melting. 相似文献
9.
There is ongoing debate as to the subduction direction of the Bangong–Nujiang Ocean during the Mesozoic (northward, southward or bidirectional subduction). Arc-related intermediate to felsic intrusions could mark the location of the subduction zone and, more importantly, elucidate the dominant geodynamic processes. We report whole rock geochemical and zircon U–Pb and Hf isotopic data for granitoids from the west central Lhasa subterrane (E80° to E86°). All rocks show metaluminous to peraluminous, calc-alkaline signatures, with strong depletion of Nb, Ta and Ti, enrichment of large ion lithophile elements (e.g., Cs, Rb, K), a negative correlation between SiO2 and P2O5, and a positive correlation between Rb and Th. All these features are indicative of I-type arc magmatism. New zircon U–Pb results, together with data from the literature, indicate continuous magmatism from the Late Jurassic to the Early Cretaceous (160 to 130 Ma). Zircon U–Pb ages for samples from the northern part of the west central Lhasa subterrane (E80° to E82°30′) yielded formation ages of 165 to 150 Ma, whereas ages of 142 to 130 Ma were obtained on samples from the south. This suggests flat or low-angle subduction of the Bangong–Nujiang Ocean, consistent with a slight southward decrease in zircon εHf(t) values for Late Jurassic rocks. Considering the crustal shortening, the distance from the Bangong–Nujiang suture zone, and a typical subduction zone melting depth of ~ 100 km, the subduction angle was less than 14° for Late Jurassic magmatism in the central Lhasa interior, consistent with flat or low-angle subduction. Compared with Late Jurassic rocks (main εHf(t) values of − 16 to − 7), Early Cretaceous rocks (145 to 130 Ma) show markedly higher εHf(t) values (mainly − 8 to 0), possibly indicating slab roll-back, likely caused by slab foundering or break-off. Combined with previously published works on arc magmatism in the central Lhasa and west part of the southern Qiangtang subterranes, our results support the bidirectional subduction of the Bangong–Nujiang Ocean along the Bangong–Nujiang Suture Zone, and indicates flat or low-angle southward subduction (165 to 145 Ma) followed by slab roll-back (145 to 130 Ma). 相似文献
10.
Chromitites enclosed within metasomatised Finero phlogopite peridotite (FPP) contain accessory platinum-group minerals, base metal (BM) sulfides, baddeleyite, zircon, zirconolite, uraninite and thorianite. To provide new insights into mantle-crustal interaction in the Finero lithosphere this study evaluates (1) the mineral chemistry and Os-isotope composition of laurite, (2) the crystal morphology, internal structure, in-situ U-Pb, trace-element and Hf-isotope data of zircon from two chromitite localities at Alpe Polunia and Rio Creves. The osmium isotope results reveal a resticted range of ‘unradiogenic’ 187Os/188Os values for laurite at Alpe Polunia (0.1247–0.1251, mean 0.1249 ± 0.0001). Re-Os model ages (TRD) of laurite reflect an Early Paleozoic partial melting event (ca 450 Ma or older), presumably before the Variscan orogeny. The Os isotopic composition of laurite/chromitite probably preserves their mantle signature and was not affected by later metasomatic processes. U-Pb and Hf-isotope data show that the Finero chromitites have distinct zircon populations with peculiar morphology, internal cathodoluminescence textures, trace-element composition and an overall U-Pb age span from ∼310 Ma to 190 Ma. Three age peaks at Rio Creves (220 ± 4 Ma, 234.2 ± 4.5 Ma and 277.5 ± 3.2 Ma) are consistent with a prolonged formation and multistage zircon growth, in contrast to the common assumption of a single metasomatic event during chromitite formation. The trace-element signatures of zircons are comparable with those of mantle-derived zircons from alkaline ultramafic rocks, supporting the carbonatitic nature of the metasomatism. Hf-isotope compositions of the Finero zircons, with εHf values ranging mainly from −3 to +1, are consistent with crustal input during metasomatism and could indicate that the parental melts/fluids were derived from a relatively old source; the minimum estimates for Hf model ages are 0.8–1.0 Ga. Our findings imply that mantle rocks and metasomatic events at Finero have a far more complex geological history than is commonly assumed. 相似文献
11.
A 2000 km long dextral Talas-Fergana strike–slip fault separates eastern terranes in the Kyrgyz Tien Shan from western terranes. The aim of this study was to constrain an age of dextral shearing in the central part of the fault utilizing Ar–Ar dating of micas. We also carried out a U–Pb–Hf zircon study of two different deformed granitoid complexes in the fault zone from which the micas for Ar dating were separated. Two samples of the oldest deformed Neoproterozoic granitoids in the area of study yielded U–Pb zircon SHRIMP ages 728 ± 11 Ma and 778 ± 11 Ma, characteristic for the Cryogenian Bolshoi Naryn Formation, and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and their calculated tHfc ages varied from 2.42 to 2.71 Ga. Thus varying Cryogenian ages and noticeable heterogeneity of Meso- to Paleoproterozoic crustal sources was established for mylonitic granites of the Bolshoi Naryn Formation. Two samples of mylonitized pegmatoidal granites of the Kyrgysh Complex yielded identical 206Pb/238U ages of 279 ± 5 Ma corresponding to the main peak of Late-Paleozoic post-collisional magmatism in the Tien Shan (Seltmann et al., 2011), and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and calculated tHfc ages from 2.42 to 2.71 Ga indicating derivation from a Paleoproterozoic crustal source. Microstructural studies showed that ductile/brittle deformation of pegmatoidal granites of the Kyrgysh Complex occurred at temperatures of 300–400 °C and caused resetting of the K–Ar isotope system of primary muscovite. Deformation of mylonitized granites of the Bolshoi Naryn Formation occurred under high temperature conditions and resulted in protracted growth and recrystallization of micas. The oldest Ar–Ar muscovite age of 241 Ma with a well defined plateau from a pegmatoidal granite of the Kyrgysh Complex is considered as a “minimum” age of dextral motions along this section of the fault in the Triassic while younger ages varying from 227 Ma to 199 Ma with typical staircase patterns indicate protracted growth and recrystallization of micas during ductile deformations which continued until the end of the Triassic. 相似文献
12.
Whole rock major and trace element and Sr-, Nd- and Hf-isotope data, together with zircon U-Pb, Hf- and O-isotope data, are reported for the Nb-Ta ore bearing granites from the Lingshan pluton in the Southeastern China, in order to trace their petrogenesis and related Nb-Ta mineralization. The Lingshan pluton contains hornblende-bearing biotite granite in the core and biotite granite, albite granite and pegmatite at the rim. In addition, numerous mafic microgranular enclaves occur in the Lingshan granites. Zircon SIMS U-Pb dating gives consistent crystallization ages of ca. 132 Ma for the Lingshan granitoids and enclaves, consistent with the Nb-Ta mineralization age of ∼132 Ma, indicating that mafic and felsic magmatism and Nb-Ta mineralization are coeval. The biotite granites contain hornblende, and are metaluminous to weakly peraluminous, with high initial 87Sr/86Sr ratios of 0.7071–0.7219, negative εNd(t) value of −5.9 to −0.3, εHf(t) values of −3.63 to −0.32 for whole rocks, high δ18O values and negative εHf(t) values for zircons, and ancient Hf and Nd model ages of 1.41–0.95 Ga and 1.23–1.04 Ga, indicating that they are I-type granites and were derived from partial melting of ancient lower crustal materials. They have variable mineral components and geochemical features, corresponding extensive fractionation of hornblende, biotite and feldspar, with minor fractionation of apatite. Existence of mafic microgranular enclaves in the biotite granites suggests a magma mixing/mingling process for the origin of the Lingshan granitoids, and mantle-derived mafic magmas provided the heat for felsic magma generation. In contrast, the Nb-Ta mineralized albite granites and pegmatites have distinct mineral components and geochemical features, which show that they are highly-fractionated granites with extensive melt and F-rich fluid interaction in the generation of these rocks. The fluoride-rich fluids induce the enrichment in Nb and Ta in the highly evolved melts. Therefore, we conclude that the Nb-Ta mineralization is the result of hydrothermal process rather than crystal fractionation in the Lingshan pluton, which provides a case to identify magmatic and hydrothermal processes and evaluate their relative importance as ore-forming processes. 相似文献
13.
The Central Asian Orogenic Belt (CAOB), as one of the largest accretionary orogens in the world, was built up through protracted accretion and collision of a variety of terranes due to the subduction and closure of the Paleo-Asian Ocean in the Neoproterozoic to Early Mesozoic. Located in the Uliastai continental margin of the southeastern CAOB, the Chagan Obo Temple area is essential for understanding the tectonic evolution of the southeastern part of the CAOB and its relation with the “Hegenshan Ocean”. In this study, detrital zircon U-Pb geochronology coupled with Hf isotopic analysis was performed on Paleozoic sedimentary strata in this area. Most detrital zircons from the studied samples possess oscillatory zoning and have Th/U ratios of 0.4-1.73, indicative of an igneous origin. Detrital zircons from the Ordovician to Devonian sedimentary strata yield a predominant age group at 511-490 Ma and subordinate age groups at 982-891 Ma, 834-790 Ma and ~ 574 Ma, and have a large spread of εHf(t) values (-20.77 to + 16.94). Carboniferous and Early Permian samples yield zircon U-Pb ages peaking at ~ 410 Ma and ~ 336 Ma, and have dominantly positive εHf(t) values (+ 1.30 to + 14.86). Such age populations and Hf isotopic signatures match those of magmatic rocks in the Northern Accretionary Orogen and the Mongolian arcs. A marked shift of provenance terranes from multiple sources to a single source and Hf isotope compositions from mixed to positive values occurred at some time in the Carboniferous. Such a shift implies that the Northern Accretionary Orogen was no longer a contributor of detritus in the Carboniferous to Early Permian, due to the opening of the “Hegenshan Ocean” possibly induced by the slab rollback of the subducting Paleo-Asian Ocean. 相似文献
14.
The Bastar Craton of Central India has a thick sequence of volcano–sedimentary rocks preserved in Kotri–Dongargarh belt that developed on a tonalite-trondhjemite-granodiorite (TTG) basement followed upwards by the Amgaon, Bengpal, Bailadila, and Nandgaon Groups of rocks. Here, we report the U-Pb geochronology and Lu-Hf isotope systematics and whole rock geochemistry of volcanic rocks and associated granitoids belonging to the Pitepani basalts, Bijli rhyolites, and Dongargarh granite in the Nandgaon Group of the Kotri belt. The volcanic rocks of the Nandgaon Group are bimodal in nature in which the basalts exhibit intergranular, porphyritic to spherulitic texture composed of pyroxenes, plagioclase, tremolite, actinolite, and chlorite ± Fe oxides. The rhyolites display porphyritic texture consisting of K-feldspar, quartz, and plagioclase as phenocrysts. The associated porphyritic granitoids have K-feldspar, microcline, plagioclase, and biotite phenocrysts within a groundmass of similar composition. The bimodal suite displays LILE, LREE enrichment, and HFSE depletion with significant negative Nb-Ta anomalies combined with slightly fractionated REE patterns in the basalts and highly fractionated patterns and prominent negative Eu anomalies in the rhyolites endorsing their generation in an island-arc/back-arc tectonic setting. The geochemical features of the associated granitoids indicate that these are potassic and classify as within-plate A-type granites. Zircons from the basalts show clear oscillatory zoning in their CL images. They cluster as a coherent group with 207Pb/206Pb spot ages ranging from 2446 to 2522 Ma and weighted mean age of 2471 ± 7 Ma. Zircons from the rhyolite samples are subhedral to euhedral and show simple oscillatory zoning with some heterogeneous fractured domains. The data from two samples define upper intercept ages of 2479 ± 13 Ma and 2463 ± 14 Ma. Zircon grains in the granite show clear oscillatory zoning and their U-Pb data define an upper intercept age of 2506 ± 50 Ma. The Lu-Hf isotopic data on the zircons from the basalts show initial 176Hf/177Hf ratios from 0.280925 to 0.281018. Their εHf(t) values are in the range of − 10.0 to − 6.7. The Hf-depleted model ages (TDM) are between 3038 Ma and 3171 Ma, and Hf crustal model ages (TDMC) vary from 3387–3589 Ma. The zircons from the rhyolites show initial 176Hf/177Hf ratios from 0.280919 to 0.281020 and from 0.281000 to 0.281103, respectively, with εHf(t) values varying from − 10 to − 6.4 and from − 7.5 to − 3.9. Among these, one sample shows TDM between 3038 Ma and 3182 Ma, and TDMC varies from 3377 to 3596 Ma, whereas the other sample shows ages of 2925 Ma and 3072 Ma with TDMC varying from 3208 to 3432 Ma. The initial 176Hf/177Hf ratios of the granites range from 0.280937 to 0.281062 with εHf(t) values of − 8.8 to − 4.3. The TDM shows a range of 2979 Ma and 3170 Ma, and TDMC varies from 3269 to 3541 Ma. The predominant negative εHf(t) values of zircons from these rocks suggest that the source material was evolved from the Paleoarchean crust. The geological, geochemical, and geochronological evidence suggests coeval tectonic and magmatic episodes of volcanic and plutonic activity in an island-arc setting where the arc migrated toward the continental margin and played a significant role in the Neoarchean–Paleoproterozoic crustal growth of the Kotri belt of Central India. 相似文献
15.
The first dredge samples recovered from the Batavia Knoll in the eastern Indian Ocean demonstrate it is a rifted continental fragment that now lies submerged in 2 km of water between the Perth Abyssal Plain and Wharton Basin, ~ 1600 km offshore Western Australia. This knoll is the second microcontinent to have been discovered in this region, lying ~ 180 km to the NE of Gulden Draak Knoll; both knolls rifted from the Indian margin at c. 104–101 Ma during the breakup of East Gondwana. Dredged rocks include granite, granodiorite, charnockite and quartz-rich pegmatite, preserving igneous microstructure and biotite-schlieren. The composite nature of many samples suggests derivation from a felsic igneous complex. This basement is at least partly covered by Late Cretaceous sedimentary strata. Zircon grains from five representative granitoid samples primarily display modified oscillatory zoning and U-Pb data that spread along concordia over ~ 50–70 m.y., suggesting protracted magmatism and Pb-loss during the latest Neoproterozoic–early Cambrian (c. 580–530 Ma). Despite the span in U-Pb zircon ages, the primary igneous populations exhibit a relatively narrow range of initial Hf isotopic ratios (Hfi = 0.281290–0.281814; εHfi = − 41.40 to − 23.32). This evolved nature of the Hf signature suggests derivation of melts from ancient crust (TDM2 = 4.05–2.92 Ga) with very limited juvenile input. Plate models based on sparse paleomagnetic data imply significant relative motion between India and Australia during the late Neoproterozoic–Cambrian. We suggest the new isotopic data from the Batavia Knoll granitic rocks, coupled with other regional geological constraints, are consistent with magmatic intrusion and subsequent disturbance of U-Pb systems along a late Neoproterozoic–Cambrian sinistral strike-slip margin related to Gondwana assembly. 相似文献
16.
M. Ram Mohan M. Satyanarayanan M. Santosh Paul J. Sylvester Mike Tubrett Rebecca Lam 《Gondwana Research》2013,23(2):539-557
The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541 ± 13 Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461 ± 15 Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715 ± 180 Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related ~ 2530 Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial176Hf/177Hf ratios and positive εHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth. 相似文献
17.
The recently-discovered Wenquan porphyry Mo deposit hosted in the Wenquan granite of the West Qinling Orogen has been recognized as a product of the Indosinian metallogenesis. Three generations of mineral assemblage for the deposit are identified as follows: (1) quartz–biotite–K-feldspar; (2) quartz–sulfide and (3) sulfide–calcite. Geochemical study shows that the mafic microgranular enclaves (MMEs) in the ore-bearing Wenquan granite have lower SiO2, and higher Mg# and Nb/Ta ratios than the host granite itself. Different from the granite which have zircon εHf(t) values of − 3.6–3.0 and TDM2 of 1234–890 Ma, the MMEs are characterized by the εHf(t) values of − 10.1–10.8 and TDM1 of 865–441 Ma. This can be interpreted to indicate a mixture origin of the Meso- and Neoproterozoic crust-derived component and Neoproterozoic SCLM-derived materials for the formation of the Wenquan granite, which played an essential role in the Mo mineralization. Comparative Pb isotopic data between ores and K-feldspar suggest that the Wenquan granitic magma originated from the middle-lower crust of the South China Block and the ore-forming materials were incorporated by hydrothermal fluid differentiated from the Triassic magmatic system, with minor contribution of sedimentary rocks. The δ34S values of 5.0–11.7‰ with a pronounced mode at 5.0 to 6.1‰ for the ores probably represent the sulfur incorporation of a typical magmatic hydrothermal fluid contaminated by heavy sulfur of Devonian sediments. The granite yielded the zircon U–Pb ages of 218 ± 2.4 Ma and 221 ± 1.3 Ma, as the same as the ages of 217 ± 2.0 Ma and 218 ± 2.5 Ma obtained for the MMEs. These ages are indistinguishable with the molybdenite Re–Os isochron age of 219 ± 5.2 Ma which is the timing for the Mo mineralization. Tectonically, the magmatic mixture processes of the Wenquan granite and the Mo mineralization to form the Wenquan Mo deposit contemporaneously occurred during the transition of tectonic regime from syn- to post-collision orogeny in the Qinling Orogen in the Late Triassic. 相似文献
18.
Fulai Liu Paul T. Robinson Axel Gerdes Huaimin Xue Pinghua Liu Juhn G. Liou 《Lithos》2010,117(1-4):247-268
Granitic leucosome and pegmatite are widely distributed within biotite-bearing orthogneiss in the northern part of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. A combined study of mineral inclusions, cathodoluminescence (CL) images, U–Pb SHRIMP dates, and in situ trace element and Lu–Hf isotope analyses of zircons provided insight into the nature and timing of partial melting in these rocks. Zircon grains separated from biotite-bearing orthogneiss typically have three distinct domains: (1) pre-metamorphic (magmatic) cores with Qtz + Kfs + Pl + Ap inclusions, which record a Neoproterozoic protolith age of ～ 790 Ma, (2) mantles with Coe + Phe + Ap inclusions that record Triassic UHP age at 227 ± 3 Ma, and (3) narrow rims with quartz inclusions that record HP granulite-facies retrograde metamorphism at ～ 210 ± 3 Ma. In contrast, zircons separated from granitic leucosome have only two distinct domains: (1) the central UHP areas with Coe + Phe + Ap inclusions record Triassic UHP age of 227 ± 3 Ma, and (2) outer magmatic areas with Qtz + Kfs + Ab + Ap inclusions that record partial melting time of 212 ± 2 Ma. Zircons separated from pegmatite contain mineral inclusions of Qtz + Kfs + Ap and show regular magmatic zoning from centre to edge. The centres record partial melting time of 212 ± 2 Ma in line with the outer domains of granitic leucosome, whereas the edges give a younger age of 201 ± 2 Ma related to Pb loss and partial recrystallization during late Triassic regional amphibolite-facies retrogression. These data indicate that partial melting in the north Sulu UHP gneissic rocks took place during post-UHP, retrograde HP granulite-facies metamorphism.Pre-metamorphic (magmatic) zircon cores from biotite-bearing orthogneiss give uniform 176Hf/177Hf of 0.28187 ± 0.00003 (2 SD; standard deviation) corresponding to εHf(790) and Hf model ages (TDM2) of about ? 16.3 and 2.41 Ga, respectively. This is consistent with the generation of its protolith by reworking of Paleoproterozoic to late Archean crust. In contrast, UHP zircon domains from biotite-bearing orthogneiss and granitic leucosome are characterized by distinct trace element composition with low Lu/Hf (< 0.006), low Th/U (< 0.1) and considerably higher, 176Hf/177Hf (0.28233 ± 0.00002; 2 SD) than the pre-metamorphic cores. The uniform but significantly different Hf isotope composition between the UHP (εHf(227) = ? 14.6 ± 0.8; 2 SD) and pre-metamorphic (εHf(227) = ? 27.7) domains indicates equilibration of the Lu–Hf isotope system only within the UHP metamorphic mineral assemblage. The disequilibrium between whole rock and UHP zircon suggests that about two thirds of the whole rock Hf retained in the pre-metamorphic zircon domains. Zircon domains crystallized during partial melting at 212 Ma in granitic leucosome and pegmatites have a Hf isotope composition indistinguishable from that of the UHP zircon domains. This suggests that only Hf (and Zr) equilibrated during UHP metamorphism was remobilized during partial melting while pre-metamorphic zircon remained stable or was not accessible. In contrast, the magmatic zircon edges from pegmatite have somewhat lower 176Hf/177Hf (～ 0.28216) and εHf(t) (? 17.6 ± 1.2; 2 SD) indicating some release of less radiogenic Hf for instance by dissolution of pre-metamorphic zircon during late regional amphibolite-facies retrogression. 相似文献
19.
The Luming porphyry Mo deposit and the Xulaojiugou skarn Pb–Zn deposit are located in the southeast Lesser Xing’an Range, NE China. They are about 15 km apart, and are both related to monzogranite. Mo orebodies in the Luming deposit are hosted within the medium- to fine-grained monzogranite, while Pb–Zn orebodies in the Xulaojiugou deposit are hosted by the contact zone between the medium-grained monzogranite and the marbles of the early Cambrian Qianshan Formation.LA-ICP-MS zircon U–Pb dating of the ore-related monzogranite in the Luming deposit yields crystallization age of 180.7 ± 1.6 Ma, and the medium-grained and porphyritic monzogranites from the Xulaojiugou deposit yield crystallization ages of 181.2 ± 1.1 Ma and 179.9 ± 1.0 Ma, respectively. Analyses of seven molybdenite samples from the Luming deposit display Re–Os isochron age of 177.9 ± 2.6 Ma. These results indicate that the mineralization in the Luming and Xulaojiugou deposits occurred at about 181–178 Ma. These two deposits are genetically linked and belong to a porphyry-skarn metallogenic system. Combined with the previously reported geochronological data for ore deposits in adjacent areas, we consider that the early Jurassic is an important epoch for Mo and Pb–Zn mineralization in the Lesser Xing’an Range.The monzogranites from the Luming and Xulaojiugou deposits are enriched in and Rb, Th, U, Pb and light rare earth elements (LREEs), and are depleted in Ba, Nb, Ta, P, Ti and Eu. They have positive εHf(t) values of 1.0–4.0 with two-stage Hf model ages (TDM2) of 868–1033 Ma. Whole-rock Sr and Nd isotopes show restricted ranges of initial compositions, with (87Sr/86Sr)i between 0.706346 and 0.707384 and εNd(t) between −3.5 and −1.8. These data indicate that their primary magmas originated from the partial melting of a depleted lithospheric mantle which had been metasomatized by subducted slab-derived fluids/melts. The early Jurassic magmatic–metallogenic events in the Lesser Xing’an Range are interpreted as a response to the subduction of the Paleo-Pacific Plate. 相似文献
20.
《Russian Geology and Geophysics》2016,57(6):891-906
We present results of investigation of the trace-element (REE, HFSE) and Hf isotope compositions and U-Pb age of single zircons crystallized from alkaline-carbonatite magmas of the Ilmeny-Vishnevogorsky complex (IVC) (Urals, Russia). It has been established that the geochemical characteristics of the early zircon (U-Pb age of 430-410 Ma) from alkaline rocks and carbonatites of this complex are determined mainly by the magmatic evolution of parental fluid-saturated alkaline-carbonatite melts and are highly associated with the cocrystallization of zircon and uranium-containing rare-metal minerals (gatchettolite and pyrochlore) at the final stages of the magmatic-system activity. The early zircons have a moderately depleted Hf isotope composition (eHf from + 11.3 to + 4.7), confirming the mantle nature of the magma source and indicating the participation of DM-like and enriched-source (probably, lower-crust component) substances in the magma generation. The considerable variations in the initial Hf isotope composition of the early zircons testify to the multistage zircon crystallization involving new portions of melts with different isotope compositions controlled by mixing of substances at their source. Late IVC zircons (250-350 Ma) have strongly disturbed “rejuvenated” isotope systems and a geochemical composition different from that of the magmatic zircons. They formed apparently at the metamorphic stage of the IVC evolution without a significant input of additional material. 相似文献