Zircon U-Pb ages, Hf isotope data and whole-rock major and trace element data for the Middle to Late Ordovician gabbros and granites in the Erguna Massif, NE China were presented in this paper. The petrogenesis of the...Zircon U-Pb ages, Hf isotope data and whole-rock major and trace element data for the Middle to Late Ordovician gabbros and granites in the Erguna Massif, NE China were presented in this paper. The petrogenesis of these rocks and the Early Paleozoic tectonic evolution of the massif were discussed. Zircons from the granites and gabbros are of magmatic origin based on their cathodoluminescence（CL） images. The 206Pb/238 U ages obtained from 20 spots on zircons from the granites range from 446±9 to 464±10 Ma, yielding a weighted mean age of 455±10 Ma; and 16 spots on zircons from the gabbros range from 465±10 to 466±7 Ma, yielding a weighted mean age of 465±2 Ma. Chemically, the Late Ordovician granites in the Erguna Massif are weakly peraluminous and similar to A-type granites. The granites and gabbros are all enriched in light rare earth elements and large ion lithophile elements（e.g., Rb, K）, and depleted in heavy rare earth elements and high field strength elements（e.g., Nb, Ta, and Ti）; they all exhibit marked negative Eu anomalies. Their zircon εHf（t） values range mainly from ＋1.86 to ＋6.21（for the granites） and ＋1.39 to ＋3.89（for the gabbros）, except for one spot with a value of-0.27（for a gabbro）. The TDM1 ages for the gabbros and TDM2 ages for the granites vary from 928 to 1 091 Ma and from 1 287 to 1 675 Ma, respectively. It is concluded that the primary magma of the granites could have been derived by partial melting of Mesoproterozoic newly accreted crustal material, whereas the primary magma of the gabbros originated by partial melting of a depleted mantle wedge that had been metasomatized by fluids derived from a subducted slab. These Middle-Late Ordovician granites and gabbros constitute a typical bimodal igneous rock association, implying an extensional environment that was probably related to the post-collisional development of the Erguna and Xing＇an massifs in the early Early Paleozoic.展开更多
This paper summarizes the geochronological, geochemical and zircon Hf isotopic data for Mesozoic granitoids within the Erguna Massif, NE China, and discusses the spatial-temporal variation of zircon Hf isotopic compos...This paper summarizes the geochronological, geochemical and zircon Hf isotopic data for Mesozoic granitoids within the Erguna Massif, NE China, and discusses the spatial-temporal variation of zircon Hf isotopic compositions, with the aim of constraining the accretion and reworking processes of continental crust within the Erguna Massif, and shedding light on the crustal evolution of the eastern segment of the Central Asian Orogenic Belt. Based on the zircon U-Pb dating results, the Mesozoic granitic magmatisms within the Erguna Massif can be subdivided into five stages: Early-Middle Triassic(249–237 Ma), Late Triassic(229–201 Ma), Early-Middle Jurassic(199–171 Ma), Late Jurassic(155–149 Ma), and Early Cretaceous(145–125 Ma).The Triassic to Early-Middle Jurassic granitoids are mainly I-type granites and minor adakitic rocks, whereas the Late Jurassic to Early Cretaceous granitoids are mainly A-type granites. This change in magmatism is consistent with the southward subduction of the Mongol-Okhotsk oceanic plate and subsequent collision and crustal thickening, followed by post-collision extension. Zircon Hf isotopic data indicate that crustal accretion of the Erguna Massif occurred in the Mesoproterozoic and Neoproterozoic. ZirconεHf(t) values increase gradually over time, whereas two-stage model(TDM2) ages decrease throughout the Mesozoic. The latter result indicates a change in the source of granitic magmas from the melting of ancient crust to more juvenile crust. Zircon εHf(t)values also exhibit spatial variations, with values decreasing northwards, whereas TDM2 ages increase. This pattern suggests that,moving from south to north, there is an increasing component of ancient crustal material within the lower continental crust of the Erguna Massif. Even if at the same latitude, the zircon Hf isotopic compositions are also inconsistent. These results reveal lateral and vertical heterogeneities in the lower continental crust of the Erguna Massif during the Mesozoic, which we use as the basis of a structural and tectonic model for this region.展开更多
The Luoguhe intrusion, located in MoheCounty, Heilongjiang Province, is mainly composed of mon-zogranite, quartz diorite and granodiorite, with minor dio-rite, tonalite, quartz monzodiorite, quartz monzonite, syeno-gr...The Luoguhe intrusion, located in MoheCounty, Heilongjiang Province, is mainly composed of mon-zogranite, quartz diorite and granodiorite, with minor dio-rite, tonalite, quartz monzodiorite, quartz monzonite, syeno-granite and alkali-feldspar granite. The intrusion can bedivided into two lithological units, i.e. quartz diorite andmonzogranite units, with affinities to high-K calc-alkalineseries. The quartz diorite unit (SiO2: 54.79%―58.30%Na2O/CaO: 0.79―1.53 and Shand index: 0.77―0.82) belongsto metaluminous rocks. And the monzogranite unit (SiO2:65.29%―66.45%, Na2O/CaO: 1.73―3.43 and Shand index<1.05) can be considered as weakly peraluminous rocks. Theintrusion is characterized by high REE abundance (∑REE =180.2―344.3 μg/g), medium-strong negative Eu anomalies(δ Eu = 0.33―0.82), weak REE fractionation [(La/Yb)N =4.12―10.45], enrichments in Rb, Th, U, K, La, Ce, Nd, HfZr and Sm, but strong depletions of Ba, Nb, Ta, Sr, P and TiThese characteristics of major, REE and trace elements in-dicate that the intrusion was formed in a transitional tectonicsetting from compressional to extensional regime, which canbe classified as post-collisional granitoids. SHRIMP U-Pbzircon analyses yield ages of 517±9 and 504±8 Ma for thequartz diorite and monzogranite units, respectively. The dis-covery of Early Paleozoic post-collisional granites in thenorthern margin of the Erguna massif indicates that thenorthern branch of Paleo-Asian Ocean between Siberianplate and Erguna massif was closed in the Early Paleozoicand the Salair orogeny ended ca. 500 Ma ago.展开更多
基金financially supported by the National Key Basic Research Program of China (Nos. 2013CB429802 and 2013CB429803)the National Natural Science Foundation of China (No. 41272077)by the Opening Foundation of the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan (No. GPMR201104)
文摘Zircon U-Pb ages, Hf isotope data and whole-rock major and trace element data for the Middle to Late Ordovician gabbros and granites in the Erguna Massif, NE China were presented in this paper. The petrogenesis of these rocks and the Early Paleozoic tectonic evolution of the massif were discussed. Zircons from the granites and gabbros are of magmatic origin based on their cathodoluminescence（CL） images. The 206Pb/238 U ages obtained from 20 spots on zircons from the granites range from 446±9 to 464±10 Ma, yielding a weighted mean age of 455±10 Ma; and 16 spots on zircons from the gabbros range from 465±10 to 466±7 Ma, yielding a weighted mean age of 465±2 Ma. Chemically, the Late Ordovician granites in the Erguna Massif are weakly peraluminous and similar to A-type granites. The granites and gabbros are all enriched in light rare earth elements and large ion lithophile elements（e.g., Rb, K）, and depleted in heavy rare earth elements and high field strength elements（e.g., Nb, Ta, and Ti）; they all exhibit marked negative Eu anomalies. Their zircon εHf（t） values range mainly from ＋1.86 to ＋6.21（for the granites） and ＋1.39 to ＋3.89（for the gabbros）, except for one spot with a value of-0.27（for a gabbro）. The TDM1 ages for the gabbros and TDM2 ages for the granites vary from 928 to 1 091 Ma and from 1 287 to 1 675 Ma, respectively. It is concluded that the primary magma of the granites could have been derived by partial melting of Mesoproterozoic newly accreted crustal material, whereas the primary magma of the gabbros originated by partial melting of a depleted mantle wedge that had been metasomatized by fluids derived from a subducted slab. These Middle-Late Ordovician granites and gabbros constitute a typical bimodal igneous rock association, implying an extensional environment that was probably related to the post-collisional development of the Erguna and Xing＇an massifs in the early Early Paleozoic.
基金supported by the MOST of China (Grant No. 2016YFC0600403)the National Natural Science Foundation of China (Grant No. 41330206)
文摘This paper summarizes the geochronological, geochemical and zircon Hf isotopic data for Mesozoic granitoids within the Erguna Massif, NE China, and discusses the spatial-temporal variation of zircon Hf isotopic compositions, with the aim of constraining the accretion and reworking processes of continental crust within the Erguna Massif, and shedding light on the crustal evolution of the eastern segment of the Central Asian Orogenic Belt. Based on the zircon U-Pb dating results, the Mesozoic granitic magmatisms within the Erguna Massif can be subdivided into five stages: Early-Middle Triassic(249–237 Ma), Late Triassic(229–201 Ma), Early-Middle Jurassic(199–171 Ma), Late Jurassic(155–149 Ma), and Early Cretaceous(145–125 Ma).The Triassic to Early-Middle Jurassic granitoids are mainly I-type granites and minor adakitic rocks, whereas the Late Jurassic to Early Cretaceous granitoids are mainly A-type granites. This change in magmatism is consistent with the southward subduction of the Mongol-Okhotsk oceanic plate and subsequent collision and crustal thickening, followed by post-collision extension. Zircon Hf isotopic data indicate that crustal accretion of the Erguna Massif occurred in the Mesoproterozoic and Neoproterozoic. ZirconεHf(t) values increase gradually over time, whereas two-stage model(TDM2) ages decrease throughout the Mesozoic. The latter result indicates a change in the source of granitic magmas from the melting of ancient crust to more juvenile crust. Zircon εHf(t)values also exhibit spatial variations, with values decreasing northwards, whereas TDM2 ages increase. This pattern suggests that,moving from south to north, there is an increasing component of ancient crustal material within the lower continental crust of the Erguna Massif. Even if at the same latitude, the zircon Hf isotopic compositions are also inconsistent. These results reveal lateral and vertical heterogeneities in the lower continental crust of the Erguna Massif during the Mesozoic, which we use as the basis of a structural and tectonic model for this region.
基金This work was supported by the National Resources Compensation from the Ministry of Land Mineral Resources of China(Grant No.2001170191).
文摘The Luoguhe intrusion, located in MoheCounty, Heilongjiang Province, is mainly composed of mon-zogranite, quartz diorite and granodiorite, with minor dio-rite, tonalite, quartz monzodiorite, quartz monzonite, syeno-granite and alkali-feldspar granite. The intrusion can bedivided into two lithological units, i.e. quartz diorite andmonzogranite units, with affinities to high-K calc-alkalineseries. The quartz diorite unit (SiO2: 54.79%―58.30%Na2O/CaO: 0.79―1.53 and Shand index: 0.77―0.82) belongsto metaluminous rocks. And the monzogranite unit (SiO2:65.29%―66.45%, Na2O/CaO: 1.73―3.43 and Shand index<1.05) can be considered as weakly peraluminous rocks. Theintrusion is characterized by high REE abundance (∑REE =180.2―344.3 μg/g), medium-strong negative Eu anomalies(δ Eu = 0.33―0.82), weak REE fractionation [(La/Yb)N =4.12―10.45], enrichments in Rb, Th, U, K, La, Ce, Nd, HfZr and Sm, but strong depletions of Ba, Nb, Ta, Sr, P and TiThese characteristics of major, REE and trace elements in-dicate that the intrusion was formed in a transitional tectonicsetting from compressional to extensional regime, which canbe classified as post-collisional granitoids. SHRIMP U-Pbzircon analyses yield ages of 517±9 and 504±8 Ma for thequartz diorite and monzogranite units, respectively. The dis-covery of Early Paleozoic post-collisional granites in thenorthern margin of the Erguna massif indicates that thenorthern branch of Paleo-Asian Ocean between Siberianplate and Erguna massif was closed in the Early Paleozoicand the Salair orogeny ended ca. 500 Ma ago.
