The Dupal anomaly has attracted widespread attention since being discovered and is regarded as the most direct manifestation of mantle inhomogeneity at present. From the initially defined anomalies limited to the sout...The Dupal anomaly has attracted widespread attention since being discovered and is regarded as the most direct manifestation of mantle inhomogeneity at present. From the initially defined anomalies limited to the southern hemisphere to the global scale, the criteria for identifying anomalies defined by Pb isotopes have also been adjusted, providing an important method and reference for the study of the mantle evolution. Pearce and Peate(1995) proposed the method of NdHf isotope and element ratio to identify the Dupal anomaly. The Nd-Hf method also offers a possible way to discriminate the mantle region of arc magmatism through the correction of Nd in the subduction process. This paper introduces the concepts and determination methods of the Dupal anomaly, and reports new Hf isotopic data of MORB-type rocks with Dupal signature in the several Tethys ophiolites. Our results of Nd-Hf method are in good agreement with those of previous Pb isotope identification. Moreover, origins and their controversy of Dupal anomaly are reviewed, and possible internal connections between Dupal anomalies and the two Large Low Shear Velocity Provinces(LLSVPs) in the lower mantle are discussed in depth. Further studies on origin and evolution of the Dupal anomaly are suggested, especially using integrated approach of Hf-Nd and Pb isotopes.展开更多
It has long been debated that the Dabie orogenic belt belongs to the North China or Yangtze craton. In recent years, eastern China has been suggested, based on the Pb isotopic compositions of Phanerozoic ore and Mesoz...It has long been debated that the Dabie orogenic belt belongs to the North China or Yangtze craton. In recent years, eastern China has been suggested, based on the Pb isotopic compositions of Phanerozoic ore and Mesozoic granitoid K-feldspar (revealing the crust Pb) in combination with Meso-Cenozoic basalts (revealing the mantle Pb), being divided into the North China and Yangtze Pb isotopic provinces, where the crust and mantle of the Yangtze craton are characterized by more radiogenic Pb. In this sense, previous researchers suggested that the pro-EW-trending Dabie orogenic belt with less radiogenic Pb in the crust was part of the North China craton. In this paper, however, the Late Cretaceous basalts in the central and southern parts of the Dabie orogenic belt are characterized by some more radiogenic Pb (\{\{\}\+\{206\}Pb\}/\{\{\}\+\{204\}Pb\}=\{17.936\}-\{18.349\}, \{\{\}\+\{207\}Pb\}/\{\{\}\+\{204\}Pb\}=\{15.500\}-\{15.688\}, \{\{\}\+\{208\}Pb\}/\{\{\}\+\{204\}Pb\}=\{38.399\}-\{38.775\}) and a unique U-Th-Pb trace element system similar to those of the Yangtze craton, showing that the Mesozoic mantle is of the Yangtze type. In addition, the decoupled Pb isotopic compositions between crust and mantle were considerably derived from their rheological inhomogeneity, implying a complicated evolution of the Dabie orogenic belt.展开更多
Voluminous Silurian–Devonian granitoids intruded a greywacke-dominated Ordovician accretionary wedge in the Chinese Altai. These granitoids are characterized by significant Nd-Hf isotopic decoupling, the underlying m...Voluminous Silurian–Devonian granitoids intruded a greywacke-dominated Ordovician accretionary wedge in the Chinese Altai. These granitoids are characterized by significant Nd-Hf isotopic decoupling, the underlying mechanism of which, so far, has been poorly understood. This issue is addressed in this study by the integration of our new and regional published geological and geochemical data. Geological studies indicated a close spatial relationship between the regional anatexis of the Ordovician wedge and the formation of the granitoids, which is characterized by a gradual textural evolution from the partial molten Ordovician wedge sedimentary rocks(the Habahe Group) to the granitoid bodies. Compositionally, these granitoids and the Ordovician Habahe Group rocks displayed close geochemical similarities, in the form of arclike trace elemental signatures as well as comparable Nd isotopic characteristics. Combined with regional available data, we suggest that the Silurian–Devonian granitoids originated from the immature and chemically primitive Habahe Group rocks. Since Nd and Hf isotopic data for the Habahe Group rocks show significant Nd-Hf isotopic decoupling, we propose that the Silurian–Devonian granitoids inherited the Nd and Hf isotopic signatures from their sources, i.e., the Habahe Group rocks. In other words, the Nd-Hf decoupling in the Habahe Group rocks is the primary causative factor leading to the prevailing Nd-Hf isotopic decoupling of the Silurian–Devonian granitoids in the Chinese Altai.展开更多
There is increasing evidence indicating that melts derived from subducted oceanic crust and sediments may have played a key role in building continental crust. This mechanism predicts that juvenile arc crust should ha...There is increasing evidence indicating that melts derived from subducted oceanic crust and sediments may have played a key role in building continental crust. This mechanism predicts that juvenile arc crust should have oxygen isotope characteristics ranging from mantle-like to supracrustal, but consistent mantle-like radiogenic(Nd-Hf) isotopic signatures. Here we present in-situ zircon U-Pb dating, Hf-O isotope analyses, and whole rock major-trace element and Nd isotope analyses of a granitoid from NW India. In-situ secondary ion mass spectrometry(SIMS) zircon U-Pb dating yields a weighted mean ^(207)Pb/^(206)Pb age of 873±6 Ma for the granitoid. It displays mantle-like zircon εHf(εHf(873 Ma)= +9.3 to +10.9) and whole-rock Nd(εNd(873 Ma)= +3.5) values but supracrustal δ^(18)O values, the latter mostly varying between 9‰ and 10‰. The calculated whole-rock δ^(18)O value of 11.3‰±0.6‰ matches well with those of hydrothermally-altered pillow lavas and sheeted dykes from ophiolites. The major and trace element composition of the granitoid is similar to petrological experimental melts derived from a mixture of MORB+sediments. Thus, the granitoid most likely represents the product of partial melting of the uppermost oceanic crust(MORB+sediments). We propose that the decoupling between Hf-Nd and O isotopes as observed in this granitoid can be used as a powerful tool for the identification of slab melting contributing to juvenile continental crustal growth. Such isotopic decoupling can also account for high δ^(18)O values observed in ancient juvenile continental crust, such as Archean tonalitetrondhjemite-granodiorite suites.展开更多
We present in situ trace element and Nd isotopic data of apatites from metamorphosed and metasomatized(i.e.,altered)and unaltered granitoids in the Songnen and Jiamusi massifs in the eastern Central Asian Orogenic Bel...We present in situ trace element and Nd isotopic data of apatites from metamorphosed and metasomatized(i.e.,altered)and unaltered granitoids in the Songnen and Jiamusi massifs in the eastern Central Asian Orogenic Belt,with the aim of fingerprinting granitoid petrogenesis,including both the magmatic and post-magmatic evolution processes.Apatites from altered granitoids(AG)and unaltered granitoids(UG)are characterized by distinct textures and geochemical compositions.Apatites from AG have irregular rim overgrowths and complex internal textures,along with low contents of rare earth elements(REEs),suggesting the re-precipitation of apatite during epidote crystallization and/or leaching of REEs from apatite by metasomatic fluids.eNd(t)values of the these apatites are decoupled from zircon eHf(t)values for most samples,which can be attributed to the higher mobility of Nd as compared to Sm in certain fluids.Apatites from UG are of igneous origin based on their homogeneous or concentric zoned textures and coupled Nd-Hf isotopic compositions.Trace element variations in igneous apatite are controlled primarily by the geochemical composition of the parental melt,fractional crystallization of other REEbearing minerals,and changes in partition coefficients.Sr contents and Eu/Eu^(*) values of apatites from UG correlate with whole-rock Sr and SiO2 contents,highlighting the effects of plagioclase fractionation during magma evolution.Apatites from UG can be subdivided into four groups based on REE contents.Group 1 apatites have REE patterns similar to the host granitoids,but are slightly enriched in middle REEs,reflecting the influence of the parental melt composition and REE partitioning.Group 2 apatites exhibit strong light REE depletions,whereas Group 3 apatites are depleted in middle and heavy REEs,indicative of the crystallization of epidote-group minerals and hornblende before and/or during apatite crystallization,respectively.Group 4 apatites are depleted in heavy REEs,but enriched in Sr,which are features of adakites.Some unusual geochemical features of the apatites,including the REE patterns,Sr contents,Eu anomalies,and Nd isotopic compositions,indicate that inherited apatites are likely to retain the geochemical features of their parental magmas,and thus provide a record of small-scale crustal assimilation during magma evolution that is not evident from the whole-rock geochemistry.展开更多
The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd...The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd-Hf isotopic compositions to discuss its genesis, source, and tectonic setting. LA-ICP-MS zircon U-Pb dating indicates that the granite crystallized in the late Indosinian（224.8±1.6 Ma）. The granite is enriched in SiO2 and K2 O and low in CaO and Na2 O. It is strongly peraluminous with the A/CNK values of 1.09–1.20 and 1.4 vol%–2.7 vol% normal corundum. Chondrite-normalized REE patterns show slightly right-dipping shape with strongly negative Eu anomalies（δEu =0.08–0.17）. All samples show enrichment of LILEs（Cs, Rb and K） and HFSEs（U, Pb, Ce and Hf）, but have relatively low contents of Ba, Sr and Ti. The zircon saturation temperatures（Tzr） are from 711 to 740°C, which are slightly lower than the average value of typical S-type granite（764°C）. The granite has negative εNd（t） and εHf（t） values, which change from ？9.1 to ？10.1 with the peak values of ？9.2 to ？9.0 and from ？3.7 to ？12.6 with the peak values of ？6 to ？5, respectively. The C DMT（Nd） and C DMT（Hf） values are 1.74–1.82 Ga with the peak values of 1.73–1.75 Ga and 1.49–2.04 Ga with the peak values of 1.5–1.6 Ga, respectively. These characteristics reveal that the source region of the granite is dominantly late Paleoproterozoic to early Mesoproterozoic crustal materials. Seven inherited magmatic zircons are dated at the age of 248.6±4.3 Ma, which suggests the existence of the early Indosinian granite in Limu area. These zircons have the εHf（t） values of ？6.7– ？2.3, similar to those of the Daqiling granite, implying the involvement of the early Indosinian granite during the formation of the Daqiling granite. Inherited zircon of 945±11 Ma has the εHf（t） and TDM（Hf） values of 8.7 and 1.14 Ga, respectively, compatible with those of the Neoproterozoic arc magmatic rocks in the eastern Jiangnan orogenic belt. Therefore we inferred that Neoproterozoic arc magma might have been involved in the formation of the Daqiling granite, and that the Neoproterozoic arc magma belt and continent-arc collision belt between the Yangtze and Cathaysia Blocks might have extended westsouthward to Limu region. It is proposed that the underplating of mantle materials triggered by crustal extension and thinning resulted in partial melting of crustal materials to form the Daqiling granite in the late Indosinian under post-collisional tectonic setting.展开更多
The mainland of China is composed of the North China Craton,the South China Craton,the Tarim Craton and other young orogehie belts.Amongst the three cratons,the North China Craton has been studied most and noted for i...The mainland of China is composed of the North China Craton,the South China Craton,the Tarim Craton and other young orogehie belts.Amongst the three cratons,the North China Craton has been studied most and noted for its widely-distributed Archean basement rocks.In this paper,we assess and compare the geology,rock types,formation age and geochemical composition features of the Archean basements of the three cratons.They have some common characteristics,including the fact that the crustal rocks prior to the Paleoarchean and the supracrustal rocks of the Neoarehean were preserved,and Tonalite-Trondhjemtite- Granodiorite (TTG)magmatism and tectono-magmatism occurred at about 2.7 Ga and about 2.5 Ga respectively.The Tarim Craton and the North China Craton show more similarities in their early Precambrian crustal evolution.Significant findings on the Archean basement of the North China Craton are coneluded to be:(1)the tectonic regime in the early stage (>3.1 Ga)is distinct from modem plate tectonics;(2)the continental crust accretion occurred mostly from the late Mesoarchean to the early Neoarehean period;(3)a huge linear tectonic belt already existed in the late Neoarchean period,suggesting the beginning of plate tectonics;and (4)the preliminary cratonization had already been completed by about 2.5 Ga. Hadean detrital zircons were found at a total of nine locations within China.Most of them show clear oscillatory zoning,sharing similar textures with magmatic zircons from interrnediate-felsic magmatic rocks. This indicates that a fair quantity of continental material had already developed on Earth at that time.展开更多
Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear e...Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear earth elements, and thus may provide specific insight into the geological processes associated with marked redoxomorphism. Multiple geochemical tracing of Sr-Nd-Ce isotopes are performed on the felsic and mafic intrusives of the Neoproterozoic（~800 Ma） Huangling complex located at the eastern Three Gorges, South China. The intrusive rocks exclusively show various extents of negative Ce anomalies. On the εCe-εNd plot, most samples from the mafic intrusions scatter within the second quadrant, whereas those from the felsic intrusions within the fourth Quadrant. Both of the two groups exhibit relatively large range of ？Ce（t） variation but limited ？Nd（t） range, which cause a deviation from the ＂crustal array＂ and reveal a decoupled Nd-Ce isotope correlation. The intermediate-felsic suite have varied Ce/Ce＊ ratios but broadly proximate εCe（t） values, indicating that their negative Ce anomalies were generated during the magmatism; on the contrary, a positive correlation between εCe（t） and Ce/Ce＊ is observed for the intermediate-mafic suite, an indication of an origin of post-magmatic alteration or metamorphism for their Ce anomalies. Calculation of model age, the occurrence age of negative Ce anomalies（TCe） for the intermediate-mafic samples infers that the alteration events took place 〉350 Ma. Data showed that negative Ce anomalies of the felsic intrusions may reflect an increase of oxygen fugacity during magma ascending, rather than an inheritance from their source rocks. This explanation implies that the Neoproterozoic magmatism occurred at the continental nucleus of the Yangtze block were developing at a geodynamic context of rapidly regional uplifting.展开更多
The Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(20000 t Sn at 0.27%,236 t Ag at 122.89 g/t,15000 t Pb at 0.84%,and 38000 t Zn at 1.43%)is located in the Wandashan Terrane of the easternmost segment of the Central A...The Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(20000 t Sn at 0.27%,236 t Ag at 122.89 g/t,15000 t Pb at 0.84%,and 38000 t Zn at 1.43%)is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt.The timing of Sn-Pb-Zn-Ag polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals.The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma,respectively,indicating that Sn mineralization and magmatism occurred during the Early Cretaceous.The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb,Ta,and Ti and enriched in Rb,Th,U,and Pb.TheεHf(t)values of the granite porphyry range from 0.9 to 7.4,with an average of about 5.6 and two-stage model ages(T_(DM2))of 705–1116 Ma,with an average age of 819 Ma.The ε_(Nd)(t)values of the apatites are–1.60–0.45,with an average of–0.9,and two-stage model ages(T_(DM2))of 872–1040 Ma,with an average age of 983 Ma.The Nd-Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.展开更多
Revealing deep composition information is crucial for systematic understanding of continental crust architecture.Deep exploration has become an important trend in the development of geoscience,and using magmatic rocks...Revealing deep composition information is crucial for systematic understanding of continental crust architecture.Deep exploration has become an important trend in the development of geoscience,and using magmatic rocks and their deep-source rock inclusions as‘rock probes’to trace the earth’s deep material information has been an effective way in recent years(e.g.,Mo,2011).展开更多
The Spanish Central System(SCS)contains several suites of Palaeozoic mafic igneous intrusions with contrasting geochemical affinity:Ordovician tholeiitic metabasites,Variscan calc-alkaline gabbros(Gb1)and microdiorite...The Spanish Central System(SCS)contains several suites of Palaeozoic mafic igneous intrusions with contrasting geochemical affinity:Ordovician tholeiitic metabasites,Variscan calc-alkaline gabbros(Gb1)and microdiorites(Gb2),shoshonitic monzogabbros(Gb3)and alkaline diabases and lamprophyres(Gb4).Not all of these rocks are accurately dated,and several aspects of their genesis are still poorly understood.We present new whole-rock geochemical data(major and trace elements,and Sr-Nd isotopes),U-Pb and Lu-Hf isotopic ratios on magmatic zircons and 40 Ar/39Ar amphibole geochronology results in order to establish a precise chronology for the successive events of magmatism in the SCS,and discuss the nature of their mantle sources.Accurate ages have been determined for the Variscan gabbros(305-294 Ma),the microdiorites(299 Ma)and the accompanying felsic porphyries(292 Ma),the shoshonitic monzogabbros(285 Ma),and the alkaline diabases(274 Ma)and monzosyenites(271-264 Ma).According to this information,the Variscan mafic magmatism would be mainly concentrated in the range of 305-294 Ma,with a final manifestation represented by the minor shoshonitic dykes.The alkaline magmatism proved to be slightly older than previously thought and yielded at least two distinct pulses:diabases and lamprophyres-monzosyenites.Zircon Hf isotopes evidence the involvement of depleted and slightly enriched mantle sources.The bulk of the eHf values are in the broad range of-8 to+11,indicative of melting both depleted and enriched mantle regions.The high within-sample Hf isotope variation(up to-11 epsilon units)shown by samples from the Variscan series(gabbros,microdiorites and monzogabbros)could be explained mainly by hybridisation of magmas derived from heterogeneous lithospheric mantle sources.Pressure estimates indicate that the Variscan mafic magmas were extracted from the lithosphere.The Nd-Hf isotopic composition of these suites of rocks suggests the recycling of pelitic sediments during the Cadomian orogeny.Deeper(asthenospheric)mantle levels were involved in the generation of the alkaline suite,whose anomalous negative eHf values(moderately decoupled with respect to radiogenic Nd)could be associated with subducted oceanic components raised by mantle upwelling associated with lithosphere thinning and extension during the Permian.展开更多
基金funded by the National Key Research and Development Project of China (Project 2020YFA0714800)。
文摘The Dupal anomaly has attracted widespread attention since being discovered and is regarded as the most direct manifestation of mantle inhomogeneity at present. From the initially defined anomalies limited to the southern hemisphere to the global scale, the criteria for identifying anomalies defined by Pb isotopes have also been adjusted, providing an important method and reference for the study of the mantle evolution. Pearce and Peate(1995) proposed the method of NdHf isotope and element ratio to identify the Dupal anomaly. The Nd-Hf method also offers a possible way to discriminate the mantle region of arc magmatism through the correction of Nd in the subduction process. This paper introduces the concepts and determination methods of the Dupal anomaly, and reports new Hf isotopic data of MORB-type rocks with Dupal signature in the several Tethys ophiolites. Our results of Nd-Hf method are in good agreement with those of previous Pb isotope identification. Moreover, origins and their controversy of Dupal anomaly are reviewed, and possible internal connections between Dupal anomalies and the two Large Low Shear Velocity Provinces(LLSVPs) in the lower mantle are discussed in depth. Further studies on origin and evolution of the Dupal anomaly are suggested, especially using integrated approach of Hf-Nd and Pb isotopes.
基金ThestudywasfundedbytheNationalNaturalScienceFoundationofChina (No .497940 43)andtheOpenLaboratoryofCon stitution ,InteractionandDynamicsoftheCrust MantleSystem China .
文摘It has long been debated that the Dabie orogenic belt belongs to the North China or Yangtze craton. In recent years, eastern China has been suggested, based on the Pb isotopic compositions of Phanerozoic ore and Mesozoic granitoid K-feldspar (revealing the crust Pb) in combination with Meso-Cenozoic basalts (revealing the mantle Pb), being divided into the North China and Yangtze Pb isotopic provinces, where the crust and mantle of the Yangtze craton are characterized by more radiogenic Pb. In this sense, previous researchers suggested that the pro-EW-trending Dabie orogenic belt with less radiogenic Pb in the crust was part of the North China craton. In this paper, however, the Late Cretaceous basalts in the central and southern parts of the Dabie orogenic belt are characterized by some more radiogenic Pb (\{\{\}\+\{206\}Pb\}/\{\{\}\+\{204\}Pb\}=\{17.936\}-\{18.349\}, \{\{\}\+\{207\}Pb\}/\{\{\}\+\{204\}Pb\}=\{15.500\}-\{15.688\}, \{\{\}\+\{208\}Pb\}/\{\{\}\+\{204\}Pb\}=\{38.399\}-\{38.775\}) and a unique U-Th-Pb trace element system similar to those of the Yangtze craton, showing that the Mesozoic mantle is of the Yangtze type. In addition, the decoupled Pb isotopic compositions between crust and mantle were considerably derived from their rheological inhomogeneity, implying a complicated evolution of the Dabie orogenic belt.
基金supported by the National Key R&D Program of China(No.2017YFC0601205)the Strategic Priority Research Program(B)of the CAS(No.XDB18020203)+4 种基金the NSF China(No.41672056)the Guangdong Special Support ProgramGIG-CAS 135 Project(No.135TP201601)A 100 Talents Program of the CAS to Yingde Jianga China Postdoctoral Science Foundation to Yu Yang(No.2018M633172)
文摘Voluminous Silurian–Devonian granitoids intruded a greywacke-dominated Ordovician accretionary wedge in the Chinese Altai. These granitoids are characterized by significant Nd-Hf isotopic decoupling, the underlying mechanism of which, so far, has been poorly understood. This issue is addressed in this study by the integration of our new and regional published geological and geochemical data. Geological studies indicated a close spatial relationship between the regional anatexis of the Ordovician wedge and the formation of the granitoids, which is characterized by a gradual textural evolution from the partial molten Ordovician wedge sedimentary rocks(the Habahe Group) to the granitoid bodies. Compositionally, these granitoids and the Ordovician Habahe Group rocks displayed close geochemical similarities, in the form of arclike trace elemental signatures as well as comparable Nd isotopic characteristics. Combined with regional available data, we suggest that the Silurian–Devonian granitoids originated from the immature and chemically primitive Habahe Group rocks. Since Nd and Hf isotopic data for the Habahe Group rocks show significant Nd-Hf isotopic decoupling, we propose that the Silurian–Devonian granitoids inherited the Nd and Hf isotopic signatures from their sources, i.e., the Habahe Group rocks. In other words, the Nd-Hf decoupling in the Habahe Group rocks is the primary causative factor leading to the prevailing Nd-Hf isotopic decoupling of the Silurian–Devonian granitoids in the Chinese Altai.
基金This work was supported by the National Key R&D Program of China(No.2017YFC0601302)the Research Start-up Project for Introduced Talent of Yunnan University(No.20190043)the Australian Research Council grants to Zheng-Xiang Li(Nos.DP0770228,FL150100133)。
文摘There is increasing evidence indicating that melts derived from subducted oceanic crust and sediments may have played a key role in building continental crust. This mechanism predicts that juvenile arc crust should have oxygen isotope characteristics ranging from mantle-like to supracrustal, but consistent mantle-like radiogenic(Nd-Hf) isotopic signatures. Here we present in-situ zircon U-Pb dating, Hf-O isotope analyses, and whole rock major-trace element and Nd isotope analyses of a granitoid from NW India. In-situ secondary ion mass spectrometry(SIMS) zircon U-Pb dating yields a weighted mean ^(207)Pb/^(206)Pb age of 873±6 Ma for the granitoid. It displays mantle-like zircon εHf(εHf(873 Ma)= +9.3 to +10.9) and whole-rock Nd(εNd(873 Ma)= +3.5) values but supracrustal δ^(18)O values, the latter mostly varying between 9‰ and 10‰. The calculated whole-rock δ^(18)O value of 11.3‰±0.6‰ matches well with those of hydrothermally-altered pillow lavas and sheeted dykes from ophiolites. The major and trace element composition of the granitoid is similar to petrological experimental melts derived from a mixture of MORB+sediments. Thus, the granitoid most likely represents the product of partial melting of the uppermost oceanic crust(MORB+sediments). We propose that the decoupling between Hf-Nd and O isotopes as observed in this granitoid can be used as a powerful tool for the identification of slab melting contributing to juvenile continental crustal growth. Such isotopic decoupling can also account for high δ^(18)O values observed in ancient juvenile continental crust, such as Archean tonalitetrondhjemite-granodiorite suites.
基金supported by the National Natural Science Foundation of China(grant numbers 42072071,41772047).
文摘We present in situ trace element and Nd isotopic data of apatites from metamorphosed and metasomatized(i.e.,altered)and unaltered granitoids in the Songnen and Jiamusi massifs in the eastern Central Asian Orogenic Belt,with the aim of fingerprinting granitoid petrogenesis,including both the magmatic and post-magmatic evolution processes.Apatites from altered granitoids(AG)and unaltered granitoids(UG)are characterized by distinct textures and geochemical compositions.Apatites from AG have irregular rim overgrowths and complex internal textures,along with low contents of rare earth elements(REEs),suggesting the re-precipitation of apatite during epidote crystallization and/or leaching of REEs from apatite by metasomatic fluids.eNd(t)values of the these apatites are decoupled from zircon eHf(t)values for most samples,which can be attributed to the higher mobility of Nd as compared to Sm in certain fluids.Apatites from UG are of igneous origin based on their homogeneous or concentric zoned textures and coupled Nd-Hf isotopic compositions.Trace element variations in igneous apatite are controlled primarily by the geochemical composition of the parental melt,fractional crystallization of other REEbearing minerals,and changes in partition coefficients.Sr contents and Eu/Eu^(*) values of apatites from UG correlate with whole-rock Sr and SiO2 contents,highlighting the effects of plagioclase fractionation during magma evolution.Apatites from UG can be subdivided into four groups based on REE contents.Group 1 apatites have REE patterns similar to the host granitoids,but are slightly enriched in middle REEs,reflecting the influence of the parental melt composition and REE partitioning.Group 2 apatites exhibit strong light REE depletions,whereas Group 3 apatites are depleted in middle and heavy REEs,indicative of the crystallization of epidote-group minerals and hornblende before and/or during apatite crystallization,respectively.Group 4 apatites are depleted in heavy REEs,but enriched in Sr,which are features of adakites.Some unusual geochemical features of the apatites,including the REE patterns,Sr contents,Eu anomalies,and Nd isotopic compositions,indicate that inherited apatites are likely to retain the geochemical features of their parental magmas,and thus provide a record of small-scale crustal assimilation during magma evolution that is not evident from the whole-rock geochemistry.
基金supported by National Key Basic Research Program of China (Grant No. 2012CB416702)National Natural Science Foundation of China (Grant No. 41230315)China Geological Survey Program (Grant No. 1212011085407)
文摘The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd-Hf isotopic compositions to discuss its genesis, source, and tectonic setting. LA-ICP-MS zircon U-Pb dating indicates that the granite crystallized in the late Indosinian（224.8±1.6 Ma）. The granite is enriched in SiO2 and K2 O and low in CaO and Na2 O. It is strongly peraluminous with the A/CNK values of 1.09–1.20 and 1.4 vol%–2.7 vol% normal corundum. Chondrite-normalized REE patterns show slightly right-dipping shape with strongly negative Eu anomalies（δEu =0.08–0.17）. All samples show enrichment of LILEs（Cs, Rb and K） and HFSEs（U, Pb, Ce and Hf）, but have relatively low contents of Ba, Sr and Ti. The zircon saturation temperatures（Tzr） are from 711 to 740°C, which are slightly lower than the average value of typical S-type granite（764°C）. The granite has negative εNd（t） and εHf（t） values, which change from ？9.1 to ？10.1 with the peak values of ？9.2 to ？9.0 and from ？3.7 to ？12.6 with the peak values of ？6 to ？5, respectively. The C DMT（Nd） and C DMT（Hf） values are 1.74–1.82 Ga with the peak values of 1.73–1.75 Ga and 1.49–2.04 Ga with the peak values of 1.5–1.6 Ga, respectively. These characteristics reveal that the source region of the granite is dominantly late Paleoproterozoic to early Mesoproterozoic crustal materials. Seven inherited magmatic zircons are dated at the age of 248.6±4.3 Ma, which suggests the existence of the early Indosinian granite in Limu area. These zircons have the εHf（t） values of ？6.7– ？2.3, similar to those of the Daqiling granite, implying the involvement of the early Indosinian granite during the formation of the Daqiling granite. Inherited zircon of 945±11 Ma has the εHf（t） and TDM（Hf） values of 8.7 and 1.14 Ga, respectively, compatible with those of the Neoproterozoic arc magmatic rocks in the eastern Jiangnan orogenic belt. Therefore we inferred that Neoproterozoic arc magma might have been involved in the formation of the Daqiling granite, and that the Neoproterozoic arc magma belt and continent-arc collision belt between the Yangtze and Cathaysia Blocks might have extended westsouthward to Limu region. It is proposed that the underplating of mantle materials triggered by crustal extension and thinning resulted in partial melting of crustal materials to form the Daqiling granite in the late Indosinian under post-collisional tectonic setting.
基金the Key Program of the Ministry of Land and Resources of China (121201102000150012,DD20160121-03, 121201102000150010-04,DD20160343-01)the National Natural Science Foundation of China (41172127,41472169).
文摘The mainland of China is composed of the North China Craton,the South China Craton,the Tarim Craton and other young orogehie belts.Amongst the three cratons,the North China Craton has been studied most and noted for its widely-distributed Archean basement rocks.In this paper,we assess and compare the geology,rock types,formation age and geochemical composition features of the Archean basements of the three cratons.They have some common characteristics,including the fact that the crustal rocks prior to the Paleoarchean and the supracrustal rocks of the Neoarehean were preserved,and Tonalite-Trondhjemtite- Granodiorite (TTG)magmatism and tectono-magmatism occurred at about 2.7 Ga and about 2.5 Ga respectively.The Tarim Craton and the North China Craton show more similarities in their early Precambrian crustal evolution.Significant findings on the Archean basement of the North China Craton are coneluded to be:(1)the tectonic regime in the early stage (>3.1 Ga)is distinct from modem plate tectonics;(2)the continental crust accretion occurred mostly from the late Mesoarchean to the early Neoarehean period;(3)a huge linear tectonic belt already existed in the late Neoarchean period,suggesting the beginning of plate tectonics;and (4)the preliminary cratonization had already been completed by about 2.5 Ga. Hadean detrital zircons were found at a total of nine locations within China.Most of them show clear oscillatory zoning,sharing similar textures with magmatic zircons from interrnediate-felsic magmatic rocks. This indicates that a fair quantity of continental material had already developed on Earth at that time.
基金supported by the National Natural Science Foundation of China (Nos. 41373037, 41173048, 41503025)
文摘Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear earth elements, and thus may provide specific insight into the geological processes associated with marked redoxomorphism. Multiple geochemical tracing of Sr-Nd-Ce isotopes are performed on the felsic and mafic intrusives of the Neoproterozoic（~800 Ma） Huangling complex located at the eastern Three Gorges, South China. The intrusive rocks exclusively show various extents of negative Ce anomalies. On the εCe-εNd plot, most samples from the mafic intrusions scatter within the second quadrant, whereas those from the felsic intrusions within the fourth Quadrant. Both of the two groups exhibit relatively large range of ？Ce（t） variation but limited ？Nd（t） range, which cause a deviation from the ＂crustal array＂ and reveal a decoupled Nd-Ce isotope correlation. The intermediate-felsic suite have varied Ce/Ce＊ ratios but broadly proximate εCe（t） values, indicating that their negative Ce anomalies were generated during the magmatism; on the contrary, a positive correlation between εCe（t） and Ce/Ce＊ is observed for the intermediate-mafic suite, an indication of an origin of post-magmatic alteration or metamorphism for their Ce anomalies. Calculation of model age, the occurrence age of negative Ce anomalies（TCe） for the intermediate-mafic samples infers that the alteration events took place 〉350 Ma. Data showed that negative Ce anomalies of the felsic intrusions may reflect an increase of oxygen fugacity during magma ascending, rather than an inheritance from their source rocks. This explanation implies that the Neoproterozoic magmatism occurred at the continental nucleus of the Yangtze block were developing at a geodynamic context of rapidly regional uplifting.
基金supported by the Chinese Central Government for Basic Scientific Research Operations in Commonwealth Research Institutes(KK 2013,KK2105)the Chinese Geological Survey Program(DD20190193,DD20211410)+1 种基金the National Key Research and Development Program of China(2017YFC0601303)the National Natural Science Foundation of China(41602075,41602066)。
文摘The Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(20000 t Sn at 0.27%,236 t Ag at 122.89 g/t,15000 t Pb at 0.84%,and 38000 t Zn at 1.43%)is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt.The timing of Sn-Pb-Zn-Ag polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals.The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma,respectively,indicating that Sn mineralization and magmatism occurred during the Early Cretaceous.The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb,Ta,and Ti and enriched in Rb,Th,U,and Pb.TheεHf(t)values of the granite porphyry range from 0.9 to 7.4,with an average of about 5.6 and two-stage model ages(T_(DM2))of 705–1116 Ma,with an average age of 819 Ma.The ε_(Nd)(t)values of the apatites are–1.60–0.45,with an average of–0.9,and two-stage model ages(T_(DM2))of 872–1040 Ma,with an average age of 983 Ma.The Nd-Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.
基金jointly supported by the National Key Technologies R&D Program of China(Grant nos.2019YFA0708600,2018YFC0603702)National Natural Science Foundation of China(Grant nos.41802074,41830216)+1 种基金China Geological Survey projects(Grant nos.DD20190001,DD20190370)a contribution to IGCP Project 662
文摘Revealing deep composition information is crucial for systematic understanding of continental crust architecture.Deep exploration has become an important trend in the development of geoscience,and using magmatic rocks and their deep-source rock inclusions as‘rock probes’to trace the earth’s deep material information has been an effective way in recent years(e.g.,Mo,2011).
基金supported by the CGL2016-78796 project of the Ministerio de Economiay Competitividad of Spain and the UCM Research Group 2018/19 n°910492。
文摘The Spanish Central System(SCS)contains several suites of Palaeozoic mafic igneous intrusions with contrasting geochemical affinity:Ordovician tholeiitic metabasites,Variscan calc-alkaline gabbros(Gb1)and microdiorites(Gb2),shoshonitic monzogabbros(Gb3)and alkaline diabases and lamprophyres(Gb4).Not all of these rocks are accurately dated,and several aspects of their genesis are still poorly understood.We present new whole-rock geochemical data(major and trace elements,and Sr-Nd isotopes),U-Pb and Lu-Hf isotopic ratios on magmatic zircons and 40 Ar/39Ar amphibole geochronology results in order to establish a precise chronology for the successive events of magmatism in the SCS,and discuss the nature of their mantle sources.Accurate ages have been determined for the Variscan gabbros(305-294 Ma),the microdiorites(299 Ma)and the accompanying felsic porphyries(292 Ma),the shoshonitic monzogabbros(285 Ma),and the alkaline diabases(274 Ma)and monzosyenites(271-264 Ma).According to this information,the Variscan mafic magmatism would be mainly concentrated in the range of 305-294 Ma,with a final manifestation represented by the minor shoshonitic dykes.The alkaline magmatism proved to be slightly older than previously thought and yielded at least two distinct pulses:diabases and lamprophyres-monzosyenites.Zircon Hf isotopes evidence the involvement of depleted and slightly enriched mantle sources.The bulk of the eHf values are in the broad range of-8 to+11,indicative of melting both depleted and enriched mantle regions.The high within-sample Hf isotope variation(up to-11 epsilon units)shown by samples from the Variscan series(gabbros,microdiorites and monzogabbros)could be explained mainly by hybridisation of magmas derived from heterogeneous lithospheric mantle sources.Pressure estimates indicate that the Variscan mafic magmas were extracted from the lithosphere.The Nd-Hf isotopic composition of these suites of rocks suggests the recycling of pelitic sediments during the Cadomian orogeny.Deeper(asthenospheric)mantle levels were involved in the generation of the alkaline suite,whose anomalous negative eHf values(moderately decoupled with respect to radiogenic Nd)could be associated with subducted oceanic components raised by mantle upwelling associated with lithosphere thinning and extension during the Permian.
