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1.
分析了浙闽粤中生代火山岩型金银矿的硫同位素组成特征,认为对应三种不同类型矿床的硫源存在变质基底和火山岩浆,火山岩浆,火山岩浆和海水三种来源。 相似文献
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浙江东坞山银矿床的锶、铅、硫同位素研究表明,成矿与燕山早期较深源的中酸性岩浆喷发-侵入活动密切相关,东坞山次火山岩体属于幔壳同熔花岗岩系列,成矿物质主要来自火山-次火山岩浆。本区不同的火山岩、次火山岩及矿化蚀变带稀土分配型式基本相似,揭示了各带成矿流体成因上的继承性和来源的一致性。 相似文献
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浙江东部火山岩型银矿床地球化学特征 总被引:1,自引:1,他引:1
浙东火山岩型银矿床属浅成中-低温火山热液成因。与成矿有关的火山岩、次火山岩具有富硅、贫铁、高钾、低钠特点。稀土元素表明,成矿火山岩与次火山岩是由地壳部分熔融形成的。同位素组成具岩浆成因特征。 相似文献
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闹牛山铜矿床次火山岩及与成矿的关系 总被引:4,自引:0,他引:4
论述了闹牛山铜矿床的地质特征,着重阐明铜矿床受火山机构、次火山岩,隐爆角砾岩控制,并将隐爆系统角砾岩划分为隐爆角砾岩,隐爆震碎热液角砾岩和隐爆破裂隙带三种类型。讨论了火山岩岩石化学、稀土元素特征;次火山岩,隐爆系统然砾岩与成矿关系,硫同位素特征,爆裂温度特征,并提出了闹牛山铜矿为与次火山岩有关的浅成中低温热液矿术。 相似文献
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对福建紫金山地区中生代岩浆岩进行了锆石Hf同位素分析,结果表明中-晚侏罗世与早白垩世岩浆岩具有不同的Hf同位素组成.中-晚侏罗世花岗岩体具有低的εHf(t)值(-13.5~-2.9),Hf同位素的二阶段模式年龄(tDCM)峰值介于1.7~2.0 Ga,表明其主要来源于古元古代基底.早白垩世侵入-次火山岩分为四方花岗闪长岩体和紫金山次火山岩、悦洋次火山岩以及温屋次火山岩.四方岩体εHf(t)值介于-2.3~0.4,tDCM峰值介于1.3~1.4Ga;紫金山次火山岩εHf(t)值变化范围大(-8.9~5.6),tDCM峰值介于1.1~~1.5 Ga,表明两者均形成于中元古代基底和地幔物质混合作用的环境;悦洋和温屋次火山岩具有相对较低的εHf(t)(-2.7~-9.6)和较高的tDCM(峰值为1.4~1.7 Ga),表明二者来源于中-古元古代基底和少量幔源物质的混合物.早白垩世岩浆岩Hf同位素特征显示,紫金山地区的侵入-次火山岩体形成于同一岩浆源区,但岩浆源区随着时间的演化各组分及组分含量在不断变化,显示了该时期复杂的壳幔作用过程.紫金山地区中生代岩浆岩中锆石Hf同位素特征表明,中-晚侏罗世岩体与早白垩世侵入-火山岩来源于不同源区,为古太平洋板块俯冲作用不同阶段的产物. 相似文献
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The strata-bound Cu−Pb−Zn polymetallic sulfide deposits occur in metamorphic rocks of greenschist phase of the middle-upper
Proterozoic Langshan Group in central Inner Mongolia. δ34S values for sulfides range from −3.1‰ to +37.3‰, and an apparent difference is noticed between vein sulfides and those in
bedded rocks. For example, δ34S values for bedded pyrite range from +10.6‰ to +20.0‰, while those for vein pyrite vary from −3.1‰ to +14.1‰. δ34S of bedded pyrrhotite is in the range +7.9‰–+23.5‰ in comparison with +6.5‰–+17.1‰ for vein pyrrhotite. The wide scatter
of δ34S and the enrichment of heavier sulfur indicate that sulfur may have been derived from H2S as a result of bacterial reduction of sulfates in the sea water. Sulfur isotopic composition also differs from deposit to
deposit in this area because of the difference in environment in which they were formed. The mobilization of bedded sulfides
in response to regional metamorphism and magmatic intrusion led to the formation of vein sulfides.
δ18O and δ13C of ore-bearing rocks and wall rocks are within the range typical of ordinary marine facies, with the exception of lower
values for ore-bearing marble at Huogeqi probably due to diopsidization and tremalitization of carbonate rocks.
Pb isotopic composition is relatively stable and characterized by lower radio-genetic lead. The age of basement rocks was
calculated to be about 23.9 Ma and ore-forming age 7.8 Ma.207Pb/204Pb−206Pb/204Pb and208Pb/204Pb−206Pb/204Pb plots indicate that Pb may probably be derived from the lower crust or upper mantle.
It is believed that the deposits in this region are related to submarine volcanic exhalation superimposed by later regional
metamorphism and magmatic intrusion. 相似文献
12.
The western Anatolian volcanic province formed during Eocene to Recent times is one of the major volcanic belts in the Aegean–western
Anatolian region. We present new chemical (whole-rock major and trace elements, and Sr, Nd, Pb and O isotopes) and new Ar/Ar
age data from the Miocene volcanic rocks in the NE–SW-trending Neogene basins that formed on the northern part of the Menderes
Massif during its exhumation as a core complex. The early-middle Miocene volcanic rocks are classified as high-K calc-alkaline
(HKVR), shoshonitic (SHVR) and ultrapotassic (UKVR), with the Late Miocene basalts being transitional between the early-middle
Miocene volcanics and the Na-alkaline Quaternary Kula volcanics (QKV). The early-middle Miocene volcanic rocks are strongly
enriched in large ion lithophile elements (LILE), have high 87Sr/86Sr(i) (0.70631–0.71001), low 143Nd/144Nd(i) (0.512145–0.512488) and high Pb isotope ratios (206Pb/204Pb = 18.838–19.148; 207Pb/204Pb = 15.672–15.725; 208Pb/204Pb = 38.904–39.172). The high field strength element (HFSE) ratios of the most primitive early-middle Miocene volcanic rocks
indicate that they were derived from a mantle source with a primitive mantle (PM)-like composition. The HFSE ratios of the
late Miocene basalts and QKV, on the other hand, indicate an OIB-like mantle origin—a hypothesis that is supported by their
trace element patterns and isotopic compositions. The HFSE ratios of the early-middle Miocene volcanic rocks also indicate
that their mantle source was distinct from those of the Eocene volcanic rocks located further north, and of the other volcanic
provinces in the region. The mantle source of the SHVR and UKVR was influenced by (1) trace element and isotopic enrichment
by subduction-related metasomatic events and (2) trace element enrichment by “multi-stage melting and melt percolation” processes
in the lithospheric mantle. The contemporaneous SHVR and UKVR show little effect of upper crustal contamination. Trace element
ratios of the HKVR indicate that they were derived mainly from lower continental crustal melts which then mixed with mantle-derived
lavas (~20–40%). The HKVR then underwent differentiation from andesites to rhyolites via nearly pure fractional crystallization
processes in the upper crust, such that have undergone a two-stage petrogenetic evolution. 相似文献
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Jin‐Xiang Li Ke‐Zhang Qin Guang‐Ming Li Bo Xiao Jun‐Xing Zhao Lei Chen 《Geological Journal》2016,51(2):285-307
The Duolong porphyry Cu–Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole‐rock elemental and Sr–Nd–Pb isotope and zircon Hf isotopic data of syn‐ and post‐ore volcanic rocks and barren and ore‐bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu–Au mineralization. LA–ICP–MS zircon U–Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore‐bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post‐ore basaltic andesite. All the samples show high‐K calc‐alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc‐type magmas. Syn‐ and post‐ore volcanic rocks show initial Sr ratios of 0.7045–0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408–18.642, (207Pb/204Pb)t of 15.584–15.672 and positive zircon εHf(t) values of 1.3–10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore‐bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054–0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5–9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong–Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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《International Geology Review》2012,54(7):904-916
Located in the western Yangtze Block, the Qingshan Pb–Zn deposit, part of the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province, contains 0.3 million tonnes of 9.86 wt.% Pb and 22.27 wt.% Zn. Ore bodies are hosted in Carboniferous and Permian carbonate rocks, structurally controlled by the Weining–Shuicheng anticline and its intraformational faults. Ores composed of sphalerite, galena, pyrite, dolomite, and calcite occur as massive, brecciated, veinlets, and disseminations in dolomitic limestones. The C–O isotope compositions of hydrothermal calcite and S–Pb–Sr isotope compositions of Qingshan sulphide minerals were analysed in order to trace the sources of reduced sulphur and metals for the Pb–Zn deposit. δ13CPDB and δ18OSMOW values of calcite range from –5.0‰ to –3.4‰ and +18.9‰ to +19.6‰, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO2 in the hydrothermal fluid had a mixed origin of mantle, marine carbonate rocks, and sedimentary organic matter. δ34S values of sulphide minerals range from +10.7‰ to +19.6‰, similar to Devonian-to-Permian seawater sulphate (+20‰ to +35‰) and evaporite rocks (+23‰ to +28‰) in Carboniferous-to-Permian strata, suggesting that the reduced sulphur in hydrothermal fluids was derived from host-strata evaporites. Ores and sulphide minerals have homogeneous and low radiogenic Pb isotope compositions (206Pb/204Pb = 18.561 to 18.768, 207Pb/204Pb = 15.701 to 15.920, and 208Pb/204Pb = 38.831 to 39.641) that plot in the upper crust Pb evolution curve, and are similar to those of Devonian-to-Permian carbonate rocks. Pb isotope compositions suggest derivation of Pb metal from the host rocks. 87Sr/86Sr ratios of sphalerite range from 0.7107 to 0.7136 and (87Sr/86Sr)200Ma ratios range from 0.7099 to 0.7126, higher than Sinian-to-Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than Proterozoic basement rocks. This indicates that the ore strontium has a mixture source of the older basement rocks and the younger cover sequence. C–O–S–Pb–Sr isotope compositions of the Qingshan Pb–Zn deposit indicate a mixed origin of the ore-forming fluids and metals. 相似文献
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Friedrich Lucassen Wolfgang Kramer Viola Bartsch Hans-Gerhard Wilke Gerhard Franz Rolf L. Romer Peter Dulski 《Contributions to Mineralogy and Petrology》2006,152(5):571-589
The Jurassic to Early Cretaceous magmatic arc of the Andes in northern Chile was a site of major additions of juvenile magmas from the subarc mantle to the continental crust. The combined effect of extension and a near stationary position of the Jurassic to lower Cretaceous arc favoured the emplacement and preservation of juvenile magmatic rocks on a large vertical and horizontal scale. Chemical and Sr, Nd, and Pb isotopic compositions of mainly mafic to intermediate volcanic and intrusive rock units coherently indicate the generation of the magmas in a subduction regime and the dominance of a depleted subarc mantle source over contributions of the ambient Palaeozoic crust. The isotopic composition of the Jurassic (206Pb/204Pb: ∼ 18.2; 207Pb/204Pb: ∼ 15.55; 143Nd/144Nd: ∼ 0.51277; 87Sr/86Sr: ∼ 0.703–0.704) and Present (206Pb/204Pb: ∼ 18.5; 207Pb/204Pb: ∼ 15.57; 143Nd/144Nd: ∼ 0.51288; 87Sr/86Sr: ∼ 0.703–0.704) depleted subarc mantle beneath the Central and Southern Andes (18°–40°S) was likely uniform over the entire region. Small differences of isotope ratios between Jurassic and Cenozoic to Recent of subarc mantle-derived could be explained by radiogenic growth in a still uniform mantle source.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . 相似文献
16.
Peter Sprung Stephan Schuth Carsten Münker Leonore Hoke 《Contributions to Mineralogy and Petrology》2007,153(6):669-687
The geologic evolution of the New Zealand microcontinent was characterised by intermittent Cretaceous to Quaternary episodes
of intraplate volcanism. To evaluate the corresponding mantle evolution beneath New Zealand with a specific focus on the tectonic
evolution, we performed a combined major and trace element and Hf, Nd, Pb, Sr isotope investigation on a suite of representative
intraplate volcanic rocks from both main islands and the Chatham Islands. Isotopically, the data set covers a range between
“HIMU-like” end member compositions (206Pb/204Pb: 20.57, 207Pb/204Pb: 15.77, 87Sr/86Sr: 0.7030, εHf: + 3.8, εNd: + 4.2), compositions tending towards MORB (206Pb/204Pb: 19.01, 207Pb/204Pb: 15.62, 87Sr/86Sr: 0.7028, εHf: + 9.9, εNd: + 7.0) and compositions reflecting the influence of subducted sediments (206Pb/204Pb: 18.99, 207Pb/204Pb: 15.67, 87Sr/86Sr: 0.7037, εHf: + 4.4, εNd: + 3.9). Whereas volcanism on the Chatham Islands constitutes the HIMU end member of our data
set, intraplate volcanic rocks from the North Island are dominated by MORB-like compositions with relatively radiogenic 206Pb/204Pb signatures. Volcanic rocks from the South Island form a trend between the three end members. Assuming a polybaric melting
column model, the primary melt compositions reflect variations in the degree of melting, coupled to variable average melting
depths. As the three isotope and trace element end members occur throughout the volcanic episodes, the “HIMU-like” and the
sediment influenced signatures most likely originate from a heterogeneous subcontinental lithospheric mantle, whereas an asthenospheric
origin is inferred for the MORB-like component. For the South Island, affinities to HIMU wane with decreasing average melting
depths whereas MORB and sediment-like signatures become more distinct. We therefore propose a polybaric melting model involving
upper asthenospheric mantle and a lithospheric mantle source that has been modified by subduction components and veins of
fossil “HIMU-like” asthenospheric melts. The proportion of asthenospheric versus lithospheric source components is controlled
by variations in lithospheric thickness and heat flow, reflecting the different tectonic settings and rates of extension.
Generally, low degree melts preferentially tap enriched vein material with HIMU signatures. The widespread occurrence of old
Gondwana-derived lithospheric mantle beneath intraplate volcanic fields in East Gondwana is suggested by overall similarities
between New Zealand intraplate volcanic rocks and volcanic rocks in East Australia and Antarctica. The petrogenetic model
proposed here may therefore serve as a general model for the petrogenesis of Cretaceous to Recent intraplate volcanic rocks
in former East Gondwana.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Petrogenesis of isotopically unusual Pliocene olivine leucitites from Deep Springs Valley, California 总被引:2,自引:0,他引:2
High-K mafic alkalic lavas (5.4 to 3.2 wt% K2O) from Deep Springs Valley, California define good correlations of increasing incompatible element (e.g., Sr, Zr, Ba, LREE)
and compatible element contents (e.g., Ni, Cr) with increasing MgO. Strontium and Nd isotope compositions are also correlated
with MgO; 87Sr/86Sr ratios decrease and ɛNd values increase with decreasing MgO. The Sr and Nd isotope compositions of these lavas are extreme compared to most other
continental and oceanic rocks; 87Sr/86Sr ratios range from 0.7121 to 0.7105 and ɛNd values range from −16.9 to −15.4. Lead isotope ratios are relatively constant, 206Pb/204Pb ∼17.2, 207Pb/204Pb ∼15.5, and 208Pb/204Pb ∼38.6. Depleted mantle model ages calculated using Sr and Nd isotopes imply that the reservoir these lavas were derived
from has been distinct from the depleted mantle reservoir since the early Proterozoic. The Sr-Nd-Pb isotope variations of
the Deep Springs Valley lavas are unique because they do not plot along either the EM I or EM II arrays. For example, most
basalts that have low ɛNd values and unradiogenic 206Pb/204Pb ratios have relatively low 87Sr/86Sr ratios (the EM I array), whereas basalts with low ɛNd values and high 87Sr/86Sr ratios have radiogenic 206Pb/204Pb ratios (the EM II array). High-K lavas from Deep Springs Valley have EM II-like Sr and Nd isotope compositions, but EM
I-like Pb isotope compositions. A simple method for producing the range of isotopic and major- and trace-element variations
in the Deep Springs Valley lavas is by two-component mixing between this unusual K-rich mantle source and a more typical depleted
mantle basalt. We favor passage of MORB-like magmas that partially fused and were contaminated by potassic magmas derived
from melting high-K mantle veins that were stored in the lithospheric mantle. The origin of the anomalously high 87Sr/86Sr and 208Pb/204Pb ratios and low ɛNd values and 206Pb/204Pb ratios requires addition of an old component with high Rb/Sr and Th/Pb ratios but low Sm/Nd and U/Pb ratios into the mantle
source region from which these basalts were derived. This old component may be sediments that were introduced into the mantle,
either during Proterozoic subduction, or by foundering of Proterozoic age crust into the mantle at some time prior to eruption
of the lavas.
Received: 28 February 1997 / Accepted: 9 July 1998 相似文献
18.
Summary Two co-existing plutonic rocks (diorite and granodiorite) were studied from an intrusion of Variscan age in the Raztocna Valley
– Nízke Tatry Mountains, Western Carpathians. Geochemical analyses of major and trace elements constrain a volcanic arc as
emplacement environment and give the first hints of a mixture of two magmatic end-members: the so-called Prasivá granodiorite
and the Raztocna diorite. The 87Sr/86Sr(0) ratios vary between 0.7075 and 0.7118, the ε Nd(0) values range from −1.4 to −5.0. Common Pb isotopes reveal a dominant crustal source with minor influences from a mantle and
a lower crustal source.
Modelling based on Sr and Nd isotope data and using three component mixing calculations indicates that mixing of 2/3 of upper
mantle material with 1/3 upper crustal material can produce the isotopic composition of the Raztocna diorite. Very minor amounts
of lower crust were incorporated in the diorite. For the Prasivá granodiorite, the mixing ratio of upper mantle and upper
crust is similar, but a lower crustal reservoir contributed about 5–10% of the source material. 相似文献
19.
Clark M. Johnson Peter W. Lipman Gerald K. Czamanske 《Contributions to Mineralogy and Petrology》1990,104(1):99-124
Over 200 H, O, Sr, Nd, and Pb isotope analyses, in addition to geologic and petrologic constraints, document the magmatic evolution of the 28.5–19 Ma Latir volcanic field and associated intrusive rocks, which includes multiple stages of crustal assimilation, magma mixing, protracted crystallization, and open- and closed-system evolution in the upper crust. In contrast to data from younger volcanic centers in northern New Mexico, relatively low and restricted primary 18O values (+6.4 to +7.4) rule out assimilation of supracrustal rocks enriched in 18O. Initial 87Sr/86Sr ratios (0.705 to 0.708), 18O values (-2 to-7), and 206Pb/204Pb ratios (17.5 to 18.4) of metaluminous precaldera volcanic rocks and postcaldera plutonic rocks suggest that most Latir rocks were generated by fractional crystallization of substantial volumes of mantle-derived basaltic magma that had near-chondritic Nd isotope ratios, accompanied by assimilation of crustal material in two main stages: 1) assimilation of non-radiogenic lower crust, followed by 2) assimilation of middle and upper crust by inter-mediate-composition magmas that had been contaminated during the first stage. Magmatic evolution in the upper crust peaked with eruption of the peralkaline Amalia Tuff (26 Ma), which evolved from metaluminous parental magmas. A third stage of late, roofward assimilation of Proterozoic rocks in the Amalia Tuff magma is indicated by trends in initial 87Sr/86Sr and 206Pb/204Pb ratios from 0.7057 to 0.7098 and 19.5 to 18.8, respectively, toward the top of the pre-eruptive magma chamber. Highly evolved postcaldera plutons are generally fine grained and are zoned in initial 87Sr/86Sr and 206Pb/204Pb ratios, varying from 0.705 to 0.709 and 17.8 to 18.6, respectively. In contrast, the coarser-grained Cabresto Lake (25 Ma) and Rio Hondo (21 Ma) plutons have relatively homogeneous initial 87Sr/86Sr and 206Pb/204Pb ratios of approximately 0.7053 and 17.94 and 17.55, respectively. 18O values for all the postcaldera plutons overlap those of the precaldera rocks and Amalia Tuff, except for those for two late-stage rhyolite dikes associated with the Rio Hondo pluton that have 18O values of-8.6 and-9.5; these dikes are the only Latir rocks which may be largely crustal melts.Chemical and isotopic data from the Latir field suggest that large fluxes of mantle-derived basaltic magma are necessary for developing and sustaining large-volume volcanic centers. Development of a detailed model suggests that 6–15 km of new crust may have been added beneath the volcanic center; such an addition may result in significant changes in the chemical and Sr and Nd isotopic compositions of the crust, although Pb isotope ratios will remain relatively unchanged. If accompanied by assimilation, crystallization of pooled basaltic magma near the MOHO may produce substantial cumulates beneath the MOHO that generate large changes in the isotopic composition of the upper mantle. The Latir field may be similar to other large-volume, long-lived intracratonal volcanic fields that fundamentally owe their origins to extensive injection of basaltic magma into the lower parts of their magmatic systems. Such fields may overlie areas of significant crustal growth and hybridization. 相似文献
20.
Paleoproterozoic volcanic rocks in the southern margin of the North China Craton,central China:Implications for the Columbia supercontinent 总被引:1,自引:0,他引:1
The volcanic rocks of the Xiong'er Group are situated in the southern margin of the North China Craton(NCC).Research on the Xiong er Group is important to understand the tectonic evolution of the NCC and the Columbia supercontinent during the Paleoproterozoic.In this study,to constrain the age of the Xiong'er volcanic rocks and identify its tectonic environment,we report zircon LA-ICP-MS data with Hf isotope,whole-rock major and trace element compositions and Sr-Nd-Pb-Hf isotopes of the volcanic rocks of the Xiong'er Group.The Xiong'er volcanic rocks mainly consist of basaltic andesite,andesite.dacite and rhyolite,with minor basalt.Our new sets of data combined with those from previous studies indicate that Xiong'er volcanism should have lasted from 1827 Ma to 1746 Ma as the major phase of the volcanism.These volcanics have extremely low MgO.Cr and Ni contents,are enriched in LREEs and LILEs but depleted in HFSEs(Nb,Ta,and Ti),similar to arc-related volcanic rocks.They are characterized by negative zircon ε_(Hf)_(t) values of-17.4 to 8.8,whole-rock initial ~(87)Sr/~(86)Sr values of 0.7023 to 0.7177 andε_(Nd)(t) values of-10.9 to 6.4.and Pb isotopes(~(206)Pb/~(204)Pb =14.366-16.431,~(207)Pb/~(204)Pb =15.106-15.371,~(208)Pb/~(204)Pb= 32.455-37.422).The available elemental and Sr-Nd-Pb-Hf isotope data suggest that the Xiong'er volcanic rocks were sourced from a mantle contaminated by continental crust.The volcanic rocks of the Xiong'er Group might have been generated by high-degree partial melting of a lithospheric mantle that was originally modified by oceanic subduction in the Archean.Thus,we suggest that the subduction-modified lithospheric mantle occurred in an extensional setting during the breakup of the Columbia supercontinent in the Late Paleoproterozoic,rather than in an arc setting. 相似文献