Mesozoic magmatism is widespread in the eastern South China Block and has a close genetic relationship with intensive polymetallic mineralization. However, proper tectonic driver remains elusive to reconcile the broad...Mesozoic magmatism is widespread in the eastern South China Block and has a close genetic relationship with intensive polymetallic mineralization. However, proper tectonic driver remains elusive to reconcile the broad intracontinental magmatic province. This study presents integrated zircon U-Pb dating, Hf isotopes and whole-rock geochemistry of the Xiwan dioritic porphyry in the NE Jiangxi ophiolitic mélange. Zircon U-Pb dating by SIMS and LA-ICP-MS methods yielded an emplacement age of ～160 Ma for the Xiwan diorite, confirming its inclusion into the Mesozoic magmatic province in SE China, instead of a component of the Neoproterozoic ophiolitic mélange genetically. The dioritic rocks have low Si02(58.08 wt%-59.15 wt%), and high NaO(5.00 wt%-5.21 wt%) and MgO(4.60 wt%-5.24 wt%) contents with low TFeO/MgO ratios(1.02-1.09). They show an adakitic geochemical affinity but exhibit relatively low Sr/Y ratios(24.8-31.1) and high Y contents(14.6-18.3 ppm) compared to the Dexing adakitic porphyries. In addition, the Xiwan diorites have moderately evolved zircon Hf isotopic compositions(ε(t)=-6.1--0.1; T=1597-1219 Ma). These elemental and isotopic signatures suggest that the Xiwan diorite formed through partial melting of a remnant arc lower crust(i.e., early Neoproterozoic mafic arc-related rocks) in response to the underplating of coeval mafic magmas. In conjunction with the temporal-spatial distribution and complex geochemical characteristics of the Mesozoic magmatism, our case study attests to the feasibility of a flat-slab subduction model in developing the broad intracontinental magmatic province in SE China. The flat-slab delamination tends to trigger an asthenospheric upwelling and thus results in extensive partial melting of the overlying lithospheric mantle and lower crustal materials in an extensional setting during the Mesozoic.展开更多
A suite of the fossil-rich marine-land interbedded strata(Nanshuangyashan Formation) is distributed at the eastern margin of the Jiamusi massif in the eastern Heilongjiang Province, NE China. The authors had recently ...A suite of the fossil-rich marine-land interbedded strata(Nanshuangyashan Formation) is distributed at the eastern margin of the Jiamusi massif in the eastern Heilongjiang Province, NE China. The authors had recently discovered a suite of arkose beneath the marine-land interbedded strata, which overlays unconformably on the Permain granite in the eastern margin of the Jiamusi massif. The LA-ICP-MS zircon U-Pb dating indicate that all detrital zircons from the analysed four arkose samples show the four population ages of >800 Ma, 538-481 Ma, 269-250 Ma and 223-215 Ma. The former three population ages are widely recorded in the Jiamusi-Khanka massif and the Songnen massif. The later group is the minimal age population in the analyzed samples, limiting the sedimentation time of the arkoses occurred after the Late Triassic. At present, the minimal age population is not recorded in the Jiamusi massif, but the granites with the ages of 228-210 Ma are widely distributed in the Songnen-Zhangguangcai Range massif and the Khanka massif. The predominantly Permian zircons are characterized by oscillatory zoning and euhedral shapes, with variable zircon εHf(t) values(-5.5 to +11.2), indicating that they were derived from mixture sources, possibly mixed with components of the Songnen-Zhangguangcai Range massif and the Jiamusi-Khanka massif. These results, combined with regional analyses, indicate that the closing of Mudanjiang ocean and Panthalassa ocean possibly existed from Early Permian to Late Triassic.展开更多
There is a controversy regarding the amalgamation of Xing’an and Songnen Blocks along the Hegenshan-Heihe Suture(HHS)in the eastern Central Asian Orogenic Belt(CAOB).To solve this problem,we performed detailed study ...There is a controversy regarding the amalgamation of Xing’an and Songnen Blocks along the Hegenshan-Heihe Suture(HHS)in the eastern Central Asian Orogenic Belt(CAOB).To solve this problem,we performed detailed study on the granites from the Zhangdaqi area,adjacent to the north of the HHS in the northern part of the Great Xing’an Range,NE China.Geochemically,the granites in the study area are metaluminous-weak peraluminous and high-K calc-alkaline series.Trace elements of the granites show that LREEs are relatively enriched,while HREEs are relatively deficient and obvious REE fractionation.The granites are characterized by obvious negative Eu anomalies,meanwhile,they are relatively enriched in Rb,K,Th and depleted in Ba,Nb,Sr,P,Ti.All the geochemical features suggest that the granites in the Zhangdaqi area are aluminum A-type granites.The zircon LA-ICP-MS U-Pb ages of these granites are 294-298 Ma,indicating that they formed in the Early Permian.These granites also have positiveεHf(t)values(8.4-14.2)and a relatively young two-stage model age between 449 Ma and 977 Ma,implying that the magma was derived from the re-melting of the Early Paleozoic-Neoproterozoic juvenile crust.Combined with geochemical characteristics(Nb/Ta ratios of 9.0-22.2,and Zr/Hf ratios of 52.3-152.0),we believe that the magmatic source area is a mixture of partial melting of the lower crust and depleted mantle.A-type granites and bimodal volcanic rocks along the Hegenshan-Heihe Suture formed during the Late Carboniferous-Early Permian,indicating that the HHS between Xing’an and Songnen Blocks closed in the late EarlyCarboniferous.Subsequently,the Zhangdaqi area was in a post-orogenic extensional environment from Late Carboniferous to Early Permian and resulted in the formation of the A-type granites.展开更多
Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during ...Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding downstream.展开更多
基金funded by National Natural Science Foundation of China (41172200)China Geological Survey(12120113093900)
文摘Mesozoic magmatism is widespread in the eastern South China Block and has a close genetic relationship with intensive polymetallic mineralization. However, proper tectonic driver remains elusive to reconcile the broad intracontinental magmatic province. This study presents integrated zircon U-Pb dating, Hf isotopes and whole-rock geochemistry of the Xiwan dioritic porphyry in the NE Jiangxi ophiolitic mélange. Zircon U-Pb dating by SIMS and LA-ICP-MS methods yielded an emplacement age of ～160 Ma for the Xiwan diorite, confirming its inclusion into the Mesozoic magmatic province in SE China, instead of a component of the Neoproterozoic ophiolitic mélange genetically. The dioritic rocks have low Si02(58.08 wt%-59.15 wt%), and high NaO(5.00 wt%-5.21 wt%) and MgO(4.60 wt%-5.24 wt%) contents with low TFeO/MgO ratios(1.02-1.09). They show an adakitic geochemical affinity but exhibit relatively low Sr/Y ratios(24.8-31.1) and high Y contents(14.6-18.3 ppm) compared to the Dexing adakitic porphyries. In addition, the Xiwan diorites have moderately evolved zircon Hf isotopic compositions(ε(t)=-6.1--0.1; T=1597-1219 Ma). These elemental and isotopic signatures suggest that the Xiwan diorite formed through partial melting of a remnant arc lower crust(i.e., early Neoproterozoic mafic arc-related rocks) in response to the underplating of coeval mafic magmas. In conjunction with the temporal-spatial distribution and complex geochemical characteristics of the Mesozoic magmatism, our case study attests to the feasibility of a flat-slab subduction model in developing the broad intracontinental magmatic province in SE China. The flat-slab delamination tends to trigger an asthenospheric upwelling and thus results in extensive partial melting of the overlying lithospheric mantle and lower crustal materials in an extensional setting during the Mesozoic.
基金financially supported by National Natural Science Foundation of China (Grant No. 41474081)the projects from China Geological Survey(Grant No. 1212011120973)
文摘A suite of the fossil-rich marine-land interbedded strata(Nanshuangyashan Formation) is distributed at the eastern margin of the Jiamusi massif in the eastern Heilongjiang Province, NE China. The authors had recently discovered a suite of arkose beneath the marine-land interbedded strata, which overlays unconformably on the Permain granite in the eastern margin of the Jiamusi massif. The LA-ICP-MS zircon U-Pb dating indicate that all detrital zircons from the analysed four arkose samples show the four population ages of >800 Ma, 538-481 Ma, 269-250 Ma and 223-215 Ma. The former three population ages are widely recorded in the Jiamusi-Khanka massif and the Songnen massif. The later group is the minimal age population in the analyzed samples, limiting the sedimentation time of the arkoses occurred after the Late Triassic. At present, the minimal age population is not recorded in the Jiamusi massif, but the granites with the ages of 228-210 Ma are widely distributed in the Songnen-Zhangguangcai Range massif and the Khanka massif. The predominantly Permian zircons are characterized by oscillatory zoning and euhedral shapes, with variable zircon εHf(t) values(-5.5 to +11.2), indicating that they were derived from mixture sources, possibly mixed with components of the Songnen-Zhangguangcai Range massif and the Jiamusi-Khanka massif. These results, combined with regional analyses, indicate that the closing of Mudanjiang ocean and Panthalassa ocean possibly existed from Early Permian to Late Triassic.
基金supported by China Geological Survey Project (Grant NO. DD20160047-02, DD20190042-03)National Key Research and Development Program (Grant NO. 2017YFC0601300-01, 2017YFC0601401, 2017YFC 0601305-02)Qingdao Leading innovation talents project (19–3–2–19–zhc)
文摘There is a controversy regarding the amalgamation of Xing’an and Songnen Blocks along the Hegenshan-Heihe Suture(HHS)in the eastern Central Asian Orogenic Belt(CAOB).To solve this problem,we performed detailed study on the granites from the Zhangdaqi area,adjacent to the north of the HHS in the northern part of the Great Xing’an Range,NE China.Geochemically,the granites in the study area are metaluminous-weak peraluminous and high-K calc-alkaline series.Trace elements of the granites show that LREEs are relatively enriched,while HREEs are relatively deficient and obvious REE fractionation.The granites are characterized by obvious negative Eu anomalies,meanwhile,they are relatively enriched in Rb,K,Th and depleted in Ba,Nb,Sr,P,Ti.All the geochemical features suggest that the granites in the Zhangdaqi area are aluminum A-type granites.The zircon LA-ICP-MS U-Pb ages of these granites are 294-298 Ma,indicating that they formed in the Early Permian.These granites also have positiveεHf(t)values(8.4-14.2)and a relatively young two-stage model age between 449 Ma and 977 Ma,implying that the magma was derived from the re-melting of the Early Paleozoic-Neoproterozoic juvenile crust.Combined with geochemical characteristics(Nb/Ta ratios of 9.0-22.2,and Zr/Hf ratios of 52.3-152.0),we believe that the magmatic source area is a mixture of partial melting of the lower crust and depleted mantle.A-type granites and bimodal volcanic rocks along the Hegenshan-Heihe Suture formed during the Late Carboniferous-Early Permian,indicating that the HHS between Xing’an and Songnen Blocks closed in the late EarlyCarboniferous.Subsequently,the Zhangdaqi area was in a post-orogenic extensional environment from Late Carboniferous to Early Permian and resulted in the formation of the A-type granites.
基金The research was funded by the Natural Science Foundation of China(40172033)and the state volcano program of the tenth Five-Year Plan period(2001BA601B06-01-4).
文摘Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding downstream.
