The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related...The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related to the early tectonic evolution of the Earth.However,its formation era,sedimentary filling sequence,and geotectonic characteristics have always been in dispute.In this study,several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone.This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village,Tongchang Township,Yimen County.LA-ICP-MS zircon dating was conducted,achieving the crystallization age of magma of 2491±15 Ma and the metamorphic ages of about 2.3 Ga,2.0 Ga,and 1.8 Ga for the first time.Meanwhile,according to in-situ Hf isotope analysis,the zirconεHf(t)values were determined to range from−3.0 to 7.6,with an average of 2.7.Furthermore,the first-stage Hf model age(TDM1)was determined to be 2513−2916 Ma,indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean.Therefore,it is believed that the strata of the slate were deposited in the Late Neoarchean,instead of the Mesoproterozoic as determined by previous researchers.Accordingly,it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group.Instead,they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information.Furthermore,the magma ages of 2491±15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton,and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic.The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland.Meanwhile,the metamorphic ages of 2.3 Ga,2.0 Ga,and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga,1.95 Ga,and 1.85 Ga of the northern margin of the Yangtze Craton,indicating that the strata experienced Paleoproterozoic tectonic-thermal events.The study area is located on the eastern margin of Qinghai-Tibet Plateau,and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous.The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.展开更多
The Beiya porphyry-skarn Au deposit is one of the largest gold deposits in China,temporally and spatially associated with Eocene intrusions in a post-collisional setting in western Yunnan,China.In this study,we report...The Beiya porphyry-skarn Au deposit is one of the largest gold deposits in China,temporally and spatially associated with Eocene intrusions in a post-collisional setting in western Yunnan,China.In this study,we report new whole-rock geochemistry,Sr-Nd isotope,zircon U-Pb geochronology and in situ zircon Hf-O isotopes of quartz-monzonite and biotite-monzonite porphyries from the Beiya deposit.The porphyry-skarn mineralization at the Beiya deposit is mainly associated with the quartz monzonite porphyry(35.8±0.6 Ma),while the biotite-monzonite porphyry(34.3±0.5 Ma)represents a post-mineralization intrusion crosscutting the main orebodies and the quartz-monzonite porphyry.Both intrusions have high-K and adakitic composition and are characterized by high Sr/Y ratios,high SiO_(2)and Al_(2)O_(3)concentrations(SiO_(2)=69.80-73.86 wt%;Al_(2)O_(3)=14.11-15.19 wt%),and low MgO,Cr,and Ni concentrations(MgO=0.2-1.0 wt%;Cr=1.76-11.13 ppm;Ni=2.52-11.72 ppm).Their Sr-Nd isotope compositions(^(87)Sr/^(86)Sr=0.7066-0.7077;εNd(t)=−5.3 to−1.5)are consistent with the lower crustal-derived amphibolite xenoliths(^(87)Sr/^(86)Sr=0.7060-0.7100;εNd(t)=−10.0 to 0.0),indicating that they might be derived from a thickened juvenile lower crust beneath the Yangtze Craton.The biotite-monzonite porphyry has lower zirconδ^(18)O values of+5.3‰to+6.8‰and higherεHf(t)values of−2.3 to+5.5 than those of the quartz-monzonite porphyry withδ^(18)O values of+7.1‰to+8.2‰andεHf(t)values of−3.8 to+1.5,implying that they were derived from different parts of the lower crust.High Ba/La and Pb/Ce ratios suggest that the quartz-monzonite porphyry is derived from a volatiles-rich reservoir.Relatively higher La/Yb,Sm/Yb and Dy/Yb ratios of the biotite-monzonite porphyry indicate residual garnet in the source,indicating a deeper source than that of the quartz-monzonite porphyry.The hydrous components should be represented by the amphibole-rich lithologies,which has relatively shallower depth than that of the garnet-bearing mafic thickened lower crust.Our data suggest that the mineralized quartz-monzonite porphyry at the Beiya deposit is derived from partial melting of amphibole-rich lithologies in the upper part of the thickened juvenile lower crust beneath the Yangtze Craton,while the post-mineralization biotite-monzonite porphyry is derived from the basal,and volatiles-poor,part of the juvenile lower crust.展开更多
Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zh...Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zhao and Cawood, 2012）. A ca. 2.15 Ga suprasubduction zone ophiolitic melange was recongized in the Archean- Paleoproterozoic Kongling Complex of the northern Yangtze craton （Han et al., 2017）. However, the tectonic evolution in early Paleoproterozoic from 2.4 Ga to 2.2 Ga remains unclear. We report here the presence of a suite of Paleoproterozoic （2.2 Ga） granites in the Huangling dome, northern Yangtze craton, which may provide important insights into crustal growth processes in the craton prior to the assembly of Columbia.展开更多
Objective The Beiya super-large Au-rich porphyry deposit(304 t Au,2.4 g/t Au)is located within the western Yangtze craton,to the southeast of the Sanjiang Tethyan Orogen(Fig.1).The ore-forming porphyry is adakitic,cha...Objective The Beiya super-large Au-rich porphyry deposit(304 t Au,2.4 g/t Au)is located within the western Yangtze craton,to the southeast of the Sanjiang Tethyan Orogen(Fig.1).The ore-forming porphyry is adakitic,characterized by high Sr/Y and La/Yb ratios coupled with low Y and Yb contents,and is generally thought to be derived from partial melting of thickened mafic lower crust.The lower crust underneath the western Yangtze craton is mainly composed of ancient crust with Archean ages,juvenile crust resulting from the Neoproterozoic subduction(740–1000 Ma),and late Permian juvenile crust related to the Emeishan mantle plume.Which lower crustal end-member has played a critical role in genesis of the Beiya ore-forming porphyry can be constrained by zircon U-Pb ages of amphibolite xenoliths hosted in the ore-forming porphyry,because these xenoliths represent direct samples of the source.In this study,we present new zircon U-Pb ages of these amphibolite xenoliths to have insight into the nature of the Beiya adakitic porphyry source.展开更多
The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has bee...The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.展开更多
Mesoproterozoic Shennongjia Group in Shennongjia Area can be divided into three subgroups in ascender order. Of which the lower subgroup includes Yingwodong, Dayanping, Macaoyuan, Luanshigou, Dawokeng and Kuangshishan...Mesoproterozoic Shennongjia Group in Shennongjia Area can be divided into three subgroups in ascender order. Of which the lower subgroup includes Yingwodong, Dayanping, Macaoyuan, Luanshigou, Dawokeng and Kuangshishan formations;the middle subgroup is formed by Yemahe, Wenshuihe and Shicaohe formations;the upper subgroup consists of Songziyuan and Wagangxi formations. Stromatolites developed very well in the carbonate rocks of each subgroup in Shennongjia Group. Based on descriptions of stromatolites macrotypes and their characteristics, this paper studied the formation environments, discussed the relationship among types, sizes, abundance of stromatolites and sedimentary environment, and established the formation and development pattern of stromatolites. As a result, this research also reveals the paleoenvironment and paleoclimate during the period of the Shennongjia Group deposited, which is beneficial to the study of paleoenvironment, paleogeography and paleoclimate, stratigraphic succession and regional correlation of the northern edge of Yangtze block. Stromatolites of Shennongjia Group are mainly conical, columnar, domal, wavy, stratiform and stromatolite reefs. The columnar and conical stromatolites are well developed. Conical stromatolites are mainly monomers, with a variety of pyramidal types, ranging in diameter from a few millimeters to several meters and formed in the high energy subtidal zone and tidal lagoon environment. Most of the columnar stromatolites are medium to small sizes implied a wide and gentle slope environment at that time. Stratiform (including wavy) stromatolites are larger scales and extends far away and distributed most widely in almost every horizon in the carbonate rocks. Stratiform stromatolites can be formed in low energy environments such as subtidal and intertidal zones and supratidal belts. Wavy stromatolites often developed in the hydrodynamic energy condition from weak energy intertidal zone gradually strengthened to the below of the high energy supratidal. Although stromatolite reefs can be a single or multiform combination, they developed mainly consisted of laminar or small walled columnar and large domal stromatolites. Shicaohe Formation also partially developed large domical stromatolites, the depositional environment is from the upper intertidal to supratidal zone. Stromatolite in Shennongjia Group usually appears as a combination of “Stratiform (wavy)-dome-columnar-coniform ” or “stratiform-dome-coniform-columnar-dome-stratiform ” vertieally, which represents the seawater depth from shallower to deeper or from shallow to deep and then to shallow again. These phenomenons generally reflected a stable sea level and companied with a high frequency oscillation. Comprehensive researches on the stratigraphy, sedimentary facies, sedimentary environment and the stromatolite types and their characteristics in the Shennongjia Group indicated that the Shennongjia Area is located on a gentle slope of carbonate platform in the passive continental edge, generally, i.e., one of warm and humid climate shallow water zone or/and a cold-drought climate, and had been experienced with eustatic cycles during the Shennongjia Group deposited.展开更多
The western margin of Yangtze block and southwestern Sanjiang region absorbed much attention from geologists. It has been proved that there occurred a series of plate subduction, collision, assembly, rifting and break...The western margin of Yangtze block and southwestern Sanjiang region absorbed much attention from geologists. It has been proved that there occurred a series of plate subduction, collision, assembly, rifting and breakup processes between them since Palaeozoic and the tectonic evolutionary relationship between them is clear. But in Proterozoic this kind of links between them became unclear. Did they undergo the assembly and breakup processes of the Rodinia super continent? This paper will take a primary discussion on this question on the basis of basement component, structure characteristics and magmatic activities.1\ Basement features\;(1) In western margin of Yangtze block its basement is composed of crystalline basement and folded basement, a so\|called double\|layer structure. The crystalline basement is made up of Kangding group, Pudeng Formation and Dibadu Formation, among them Kangding group is a representative and composed mainly of migmatite, compositing gneiss, hornblende schist and granulitite. The isotopic age of crystalline basement is older than 1900Ma, so its geological time is late Archaean to early Proterozoic. The folded basement is composed of Dahongshan group, Hekou group, Kunyang group, Huili group and Yanbian group. Their rock associations are made up mainly of spilite\|keratophyre formation, carbonate formation, clastic rock and clastic rock formation with some basic volcanic rocks. The folded basement is assigned to be early and middle Proterozoic (1000～1700M a).展开更多
Based on outcrop, drilling, logging and seismic data, the reservoir forming conditions, reservoir forming model and exploration potential of the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze ...Based on outcrop, drilling, logging and seismic data, the reservoir forming conditions, reservoir forming model and exploration potential of the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze craton region were examined.(1) This area is in craton rifting stage from Sinian to Early Cambrian, characterized by syn-sedimentary faults and rapid subsidence, significant sedimentary differences, and development of Dengying Formation platform margins on both sides of the rift.(2) The Sinian–Cambrian in this area has two sets of high-quality source rocks, Doushantuo Formation and Maidiping-Qiongzhusi Formation;of which, the latter has a thickness of 150–600 m and hydrocarbon generation intensity of(100-200)×10;m;/km;.(3) The mounds and shoals in the platform margin of Sinian Dengying Formation controlled by faults are thick and distributed in rows and zones;they are reformed by contemporaneous–quasi-contemporaneous and supergene karstification jointly, forming pore-type reservoirs with a thickness of 200-400 m.(4) The two sets of source rocks enter oil generation windows from Permian to Early Triassic, and the oil migrates a short distance to the lithologic traps of mounds and shoals to form a huge scale paleo-oil reservoir group;from Late Triassic to Jurassic, the oil in the paleo-oil reservoirs is cracked into gas, laying the foundation of present natural gas reservoirs.(5) The mound-shoal body at the platform margin of Dengying Formation and the two sets of high-quality source rocks combine into several types of favorable source-reservoir combinations, which, with the advantage of near-source and high-efficiency reservoir formation, and can form large lithologic gas reservoirs. The Mianyang-Jiange area is a potential large gas field with trillion cubic meters of reserves. According to seismic prediction, the Laoguanmiao structure in this area has the Deng-2 Member mound-shoal reservoir of about 1300 km^(2), making it a ultra-deep target worthy of exploration in the near future.展开更多
Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate s...Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.展开更多
The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable envi...The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable environment. They are termed as the Kunyang Group, the Huili Group, and the Dongchuan Group respectively in different regions. We performed zircon U-Pb da- ting of the tuff from the groups. The results, coupled with the detrital zircon U-Pb ages of clastic rocks from the Kunyang Group and the Dongchuan Group, indicate that the sedimentation ages of the Kunyang Group and the Huili Group range from 1050 to 1000 Ma and that the Kunyang Group and the Huili Group belong to a sedimentary association with contemporaneous heterotopic facies. The detrital zircon ages and Hf isotope compositions reveal that the clastic materials in the Kunyang Group and the Huili Group are derived primarily from the Cathaysia massif. Zircons of the tuff in the Dongchuan Group yields an age of ca. 1.5 Ga and all the zircon ages of clastics in the Dongchuan Group are older than 1.5 Ga, indicating that the sedimentation of the Dongchuan Group occurred during the late Mesoproterozoic Changcheng Period. Age spectra of the detrital zircons in- dicate that the clastic materials of the Dongchuan Group are derived primarily from the ancient basement of the Yangtze mas- sif. A systematic Hf isotope determination of various types of zircons in the above three stratigraphic units shows that there is a rapid elevation in the initial Hf value of zircon at -1.5 and 1.0 Ga. Previous studies on the sedimentary characteristics of the Kunyang Group and the Huili Group show that both were deposited in a foreland basin. Combining our data with previous studies, we suggest that the Kunyang Group and the Huili Group are foreland basin sedimentary successions formed along the southern side of the Yangtze massif after an amalgamation between the Yangtze massif and the Cathaysia massif during the Grenvillian. The assembly of the Yangtze massif and the Cathaysia massif developed gradually from the west to the east and was finally completed in the eastern segment of the Yangtze massif at 0.9 Ga, representing the last stage of the Rodinia super- continent assembly, Hf isotope compositions in zircon indicate that the supercontinent cycle has an intimate relation with crus- tal growth.展开更多
基金The work was financially supported by Project of 1∶50000 Regional Geological Survey of Samaki,Yinmin,Guicheng and Shugu Sheets in Yunnan Province by Land and Resources Department of Yunnan Province(D201905)Project of 1∶50000 Regional Geological Survey of Erjie,Yimen,Mingyihe and Shangpubei Sheets in Yunnan Province(DD20160017)Regional Geological Survey Area Summary and Service Product Development in Yunnan Province by China Geological Survey(121201102000150012-02).
文摘The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related to the early tectonic evolution of the Earth.However,its formation era,sedimentary filling sequence,and geotectonic characteristics have always been in dispute.In this study,several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone.This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village,Tongchang Township,Yimen County.LA-ICP-MS zircon dating was conducted,achieving the crystallization age of magma of 2491±15 Ma and the metamorphic ages of about 2.3 Ga,2.0 Ga,and 1.8 Ga for the first time.Meanwhile,according to in-situ Hf isotope analysis,the zirconεHf(t)values were determined to range from−3.0 to 7.6,with an average of 2.7.Furthermore,the first-stage Hf model age(TDM1)was determined to be 2513−2916 Ma,indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean.Therefore,it is believed that the strata of the slate were deposited in the Late Neoarchean,instead of the Mesoproterozoic as determined by previous researchers.Accordingly,it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group.Instead,they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information.Furthermore,the magma ages of 2491±15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton,and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic.The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland.Meanwhile,the metamorphic ages of 2.3 Ga,2.0 Ga,and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga,1.95 Ga,and 1.85 Ga of the northern margin of the Yangtze Craton,indicating that the strata experienced Paleoproterozoic tectonic-thermal events.The study area is located on the eastern margin of Qinghai-Tibet Plateau,and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous.The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.
基金This work was funded by the National Key Research and Development Program of China(Grant Nos.2016YFC0600310 and 2019YFA0708602)the National Natural Science Foundation of China(Grant Nos.41702091,41872083 and 42022014)+1 种基金the Program of the China Geological Survey(Grant No.DD20160024-07),the China Fundamental Research Funds for the Central Universities(Grant No.2652018133)the 111 Project of the Ministry of Science and Technology(Grant No.BP0719021).
文摘The Beiya porphyry-skarn Au deposit is one of the largest gold deposits in China,temporally and spatially associated with Eocene intrusions in a post-collisional setting in western Yunnan,China.In this study,we report new whole-rock geochemistry,Sr-Nd isotope,zircon U-Pb geochronology and in situ zircon Hf-O isotopes of quartz-monzonite and biotite-monzonite porphyries from the Beiya deposit.The porphyry-skarn mineralization at the Beiya deposit is mainly associated with the quartz monzonite porphyry(35.8±0.6 Ma),while the biotite-monzonite porphyry(34.3±0.5 Ma)represents a post-mineralization intrusion crosscutting the main orebodies and the quartz-monzonite porphyry.Both intrusions have high-K and adakitic composition and are characterized by high Sr/Y ratios,high SiO_(2)and Al_(2)O_(3)concentrations(SiO_(2)=69.80-73.86 wt%;Al_(2)O_(3)=14.11-15.19 wt%),and low MgO,Cr,and Ni concentrations(MgO=0.2-1.0 wt%;Cr=1.76-11.13 ppm;Ni=2.52-11.72 ppm).Their Sr-Nd isotope compositions(^(87)Sr/^(86)Sr=0.7066-0.7077;εNd(t)=−5.3 to−1.5)are consistent with the lower crustal-derived amphibolite xenoliths(^(87)Sr/^(86)Sr=0.7060-0.7100;εNd(t)=−10.0 to 0.0),indicating that they might be derived from a thickened juvenile lower crust beneath the Yangtze Craton.The biotite-monzonite porphyry has lower zirconδ^(18)O values of+5.3‰to+6.8‰and higherεHf(t)values of−2.3 to+5.5 than those of the quartz-monzonite porphyry withδ^(18)O values of+7.1‰to+8.2‰andεHf(t)values of−3.8 to+1.5,implying that they were derived from different parts of the lower crust.High Ba/La and Pb/Ce ratios suggest that the quartz-monzonite porphyry is derived from a volatiles-rich reservoir.Relatively higher La/Yb,Sm/Yb and Dy/Yb ratios of the biotite-monzonite porphyry indicate residual garnet in the source,indicating a deeper source than that of the quartz-monzonite porphyry.The hydrous components should be represented by the amphibole-rich lithologies,which has relatively shallower depth than that of the garnet-bearing mafic thickened lower crust.Our data suggest that the mineralized quartz-monzonite porphyry at the Beiya deposit is derived from partial melting of amphibole-rich lithologies in the upper part of the thickened juvenile lower crust beneath the Yangtze Craton,while the post-mineralization biotite-monzonite porphyry is derived from the basal,and volatiles-poor,part of the juvenile lower crust.
基金supported by the funded project of the China Geological Survey(grants No.12120113061700,121201009000150013 and DD20160029)
文摘Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zhao and Cawood, 2012）. A ca. 2.15 Ga suprasubduction zone ophiolitic melange was recongized in the Archean- Paleoproterozoic Kongling Complex of the northern Yangtze craton （Han et al., 2017）. However, the tectonic evolution in early Paleoproterozoic from 2.4 Ga to 2.2 Ga remains unclear. We report here the presence of a suite of Paleoproterozoic （2.2 Ga） granites in the Huangling dome, northern Yangtze craton, which may provide important insights into crustal growth processes in the craton prior to the assembly of Columbia.
基金financially supported by the National Key Research and Development Program of China(grant No.2016YFC0600310)the 973 Project(2015CB452600,2011CB4031006)+2 种基金the National Natural Science Foundation of China(grants No.41872083,41472076)the Program of the China Geological Survey(grants No.DD20160024–07,DD20179172)the China Fundamental Research Funds for the Central Universities(grant No.2652018133).
文摘Objective The Beiya super-large Au-rich porphyry deposit(304 t Au,2.4 g/t Au)is located within the western Yangtze craton,to the southeast of the Sanjiang Tethyan Orogen(Fig.1).The ore-forming porphyry is adakitic,characterized by high Sr/Y and La/Yb ratios coupled with low Y and Yb contents,and is generally thought to be derived from partial melting of thickened mafic lower crust.The lower crust underneath the western Yangtze craton is mainly composed of ancient crust with Archean ages,juvenile crust resulting from the Neoproterozoic subduction(740–1000 Ma),and late Permian juvenile crust related to the Emeishan mantle plume.Which lower crustal end-member has played a critical role in genesis of the Beiya ore-forming porphyry can be constrained by zircon U-Pb ages of amphibolite xenoliths hosted in the ore-forming porphyry,because these xenoliths represent direct samples of the source.In this study,we present new zircon U-Pb ages of these amphibolite xenoliths to have insight into the nature of the Beiya adakitic porphyry source.
基金funded by the Open Foundation of the Beijing SHRIMP Center (DDC15-016)the Applied Basic Research Program Youth Project of Yunnan Province (2016DF031)the National Basic Research Program of China (2015CB452605)
文摘The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.
基金This research was co-supported by the National Key Research and Development Program of China (2016YFC0601001),the National Natural Science Foundation of China (41472082)China Geological Survey Projects (DD20160120-01)+1 种基金Globe Geopark of Shennongjia. We are grateful to the leaders of Shennongjia National Park and Mr. Zhixian Wang,Quan Zhong gave great assistances and warmly aidsthe field survey was under careful direction by Mr. Lesheng Qu from Hubei Geological Survey,Mr. Yuansheng Geng from Institute of Geology,CAGS. Sincere thanks are also given Mr. Zejiu Wang,Xin Shang and Mrs. Xiulan Ma from Chinese Academy of Geological Sciences (CAGS) and All China Commission of Stratigraphy.
文摘Mesoproterozoic Shennongjia Group in Shennongjia Area can be divided into three subgroups in ascender order. Of which the lower subgroup includes Yingwodong, Dayanping, Macaoyuan, Luanshigou, Dawokeng and Kuangshishan formations;the middle subgroup is formed by Yemahe, Wenshuihe and Shicaohe formations;the upper subgroup consists of Songziyuan and Wagangxi formations. Stromatolites developed very well in the carbonate rocks of each subgroup in Shennongjia Group. Based on descriptions of stromatolites macrotypes and their characteristics, this paper studied the formation environments, discussed the relationship among types, sizes, abundance of stromatolites and sedimentary environment, and established the formation and development pattern of stromatolites. As a result, this research also reveals the paleoenvironment and paleoclimate during the period of the Shennongjia Group deposited, which is beneficial to the study of paleoenvironment, paleogeography and paleoclimate, stratigraphic succession and regional correlation of the northern edge of Yangtze block. Stromatolites of Shennongjia Group are mainly conical, columnar, domal, wavy, stratiform and stromatolite reefs. The columnar and conical stromatolites are well developed. Conical stromatolites are mainly monomers, with a variety of pyramidal types, ranging in diameter from a few millimeters to several meters and formed in the high energy subtidal zone and tidal lagoon environment. Most of the columnar stromatolites are medium to small sizes implied a wide and gentle slope environment at that time. Stratiform (including wavy) stromatolites are larger scales and extends far away and distributed most widely in almost every horizon in the carbonate rocks. Stratiform stromatolites can be formed in low energy environments such as subtidal and intertidal zones and supratidal belts. Wavy stromatolites often developed in the hydrodynamic energy condition from weak energy intertidal zone gradually strengthened to the below of the high energy supratidal. Although stromatolite reefs can be a single or multiform combination, they developed mainly consisted of laminar or small walled columnar and large domal stromatolites. Shicaohe Formation also partially developed large domical stromatolites, the depositional environment is from the upper intertidal to supratidal zone. Stromatolite in Shennongjia Group usually appears as a combination of “Stratiform (wavy)-dome-columnar-coniform ” or “stratiform-dome-coniform-columnar-dome-stratiform ” vertieally, which represents the seawater depth from shallower to deeper or from shallow to deep and then to shallow again. These phenomenons generally reflected a stable sea level and companied with a high frequency oscillation. Comprehensive researches on the stratigraphy, sedimentary facies, sedimentary environment and the stromatolite types and their characteristics in the Shennongjia Group indicated that the Shennongjia Area is located on a gentle slope of carbonate platform in the passive continental edge, generally, i.e., one of warm and humid climate shallow water zone or/and a cold-drought climate, and had been experienced with eustatic cycles during the Shennongjia Group deposited.
文摘The western margin of Yangtze block and southwestern Sanjiang region absorbed much attention from geologists. It has been proved that there occurred a series of plate subduction, collision, assembly, rifting and breakup processes between them since Palaeozoic and the tectonic evolutionary relationship between them is clear. But in Proterozoic this kind of links between them became unclear. Did they undergo the assembly and breakup processes of the Rodinia super continent? This paper will take a primary discussion on this question on the basis of basement component, structure characteristics and magmatic activities.1\ Basement features\;(1) In western margin of Yangtze block its basement is composed of crystalline basement and folded basement, a so\|called double\|layer structure. The crystalline basement is made up of Kangding group, Pudeng Formation and Dibadu Formation, among them Kangding group is a representative and composed mainly of migmatite, compositing gneiss, hornblende schist and granulitite. The isotopic age of crystalline basement is older than 1900Ma, so its geological time is late Archaean to early Proterozoic. The folded basement is composed of Dahongshan group, Hekou group, Kunyang group, Huili group and Yanbian group. Their rock associations are made up mainly of spilite\|keratophyre formation, carbonate formation, clastic rock and clastic rock formation with some basic volcanic rocks. The folded basement is assigned to be early and middle Proterozoic (1000～1700M a).
基金Supported by the PetroChina Forward-looking and Fundamental Major Scientific and Technological Project (2021DJ0605)。
文摘Based on outcrop, drilling, logging and seismic data, the reservoir forming conditions, reservoir forming model and exploration potential of the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze craton region were examined.(1) This area is in craton rifting stage from Sinian to Early Cambrian, characterized by syn-sedimentary faults and rapid subsidence, significant sedimentary differences, and development of Dengying Formation platform margins on both sides of the rift.(2) The Sinian–Cambrian in this area has two sets of high-quality source rocks, Doushantuo Formation and Maidiping-Qiongzhusi Formation;of which, the latter has a thickness of 150–600 m and hydrocarbon generation intensity of(100-200)×10;m;/km;.(3) The mounds and shoals in the platform margin of Sinian Dengying Formation controlled by faults are thick and distributed in rows and zones;they are reformed by contemporaneous–quasi-contemporaneous and supergene karstification jointly, forming pore-type reservoirs with a thickness of 200-400 m.(4) The two sets of source rocks enter oil generation windows from Permian to Early Triassic, and the oil migrates a short distance to the lithologic traps of mounds and shoals to form a huge scale paleo-oil reservoir group;from Late Triassic to Jurassic, the oil in the paleo-oil reservoirs is cracked into gas, laying the foundation of present natural gas reservoirs.(5) The mound-shoal body at the platform margin of Dengying Formation and the two sets of high-quality source rocks combine into several types of favorable source-reservoir combinations, which, with the advantage of near-source and high-efficiency reservoir formation, and can form large lithologic gas reservoirs. The Mianyang-Jiange area is a potential large gas field with trillion cubic meters of reserves. According to seismic prediction, the Laoguanmiao structure in this area has the Deng-2 Member mound-shoal reservoir of about 1300 km^(2), making it a ultra-deep target worthy of exploration in the near future.
文摘Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.
基金supported by Chinese Geological Survey Projects (Grant Nos. 1212011121097, 1212011120130)
文摘The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable environment. They are termed as the Kunyang Group, the Huili Group, and the Dongchuan Group respectively in different regions. We performed zircon U-Pb da- ting of the tuff from the groups. The results, coupled with the detrital zircon U-Pb ages of clastic rocks from the Kunyang Group and the Dongchuan Group, indicate that the sedimentation ages of the Kunyang Group and the Huili Group range from 1050 to 1000 Ma and that the Kunyang Group and the Huili Group belong to a sedimentary association with contemporaneous heterotopic facies. The detrital zircon ages and Hf isotope compositions reveal that the clastic materials in the Kunyang Group and the Huili Group are derived primarily from the Cathaysia massif. Zircons of the tuff in the Dongchuan Group yields an age of ca. 1.5 Ga and all the zircon ages of clastics in the Dongchuan Group are older than 1.5 Ga, indicating that the sedimentation of the Dongchuan Group occurred during the late Mesoproterozoic Changcheng Period. Age spectra of the detrital zircons in- dicate that the clastic materials of the Dongchuan Group are derived primarily from the ancient basement of the Yangtze mas- sif. A systematic Hf isotope determination of various types of zircons in the above three stratigraphic units shows that there is a rapid elevation in the initial Hf value of zircon at -1.5 and 1.0 Ga. Previous studies on the sedimentary characteristics of the Kunyang Group and the Huili Group show that both were deposited in a foreland basin. Combining our data with previous studies, we suggest that the Kunyang Group and the Huili Group are foreland basin sedimentary successions formed along the southern side of the Yangtze massif after an amalgamation between the Yangtze massif and the Cathaysia massif during the Grenvillian. The assembly of the Yangtze massif and the Cathaysia massif developed gradually from the west to the east and was finally completed in the eastern segment of the Yangtze massif at 0.9 Ga, representing the last stage of the Rodinia super- continent assembly, Hf isotope compositions in zircon indicate that the supercontinent cycle has an intimate relation with crus- tal growth.
