Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history...Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period. Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma＇anshan area. Different samples within one eruption show relative identical lithologies, chemical and isotopic compositions. However, the geochemical features for the five eruptions are distinct from each other. These volcanic rocks show low Mg# values （〈45）, moderate to high fractionation of LREEs and HREEs, and enrichment of Pb and Ba and depletion of Nb. Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies. And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks. Segregated primitive magma pulsating injected into magma chamber, fractional crystallized and contaminated with crust component. Finally, magmas with distinct chemical and isotopic compositions for each eruption formed. The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.展开更多
Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd...Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd-87Sr/86Sr, 87Sr/86Sr-Sr and 87Sr/86Sr-K2O/(K2O+Na2O) indicated that the volcanic rocks were chiefly derived from the depleted mantle source and generally were not mixed crust materials. Of the samples 6 were given the mean Sm -Nd model age (TDM) of 443. 3±20. 6 Ma possibly indicating the age of chemical variation event in the magma source of the study area. Features of the trace elements indicated that the rocks from the Half Three Point Formation are of typical calc-alkaline volcanic suite and similar to those from the Tertiary volcanic rocks of the Fildes Peninsula, being the same products of the island-arc volcanic activity.展开更多
Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, Chi...Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr),=0.70895-0.71140) and low (143Nd/144Nd)1 ratios (varying from 0.51135 to 0.51231); and its δ18Osmow, whole rock values vary from +5.8%c to +10.6%c with a mean of +7.1%c. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced metasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enriched mantle in its mature stage in the back-arc spreading environment. The evolution of magmas is associated with two trends, i.e., fractional crystallization and mixing with or intensive contamination by palaeo-crust materials or metamorphic rocks. The former process is evident in the gold field system of quartz-vein type, whereas the latter is dominated in the gold field system of the altered-rock type. This conclusion is very important for more detailed study of petrogenesis and mineralization through the crust-mantle interaction (exchange) in the Mesozoic in this region.展开更多
The isotopic signature of mid\|ocean ridge basalts (MORB) from the Indian Ocean is different from that of MORB from the Pacific and North\|Atlantic oceans.. The Indian MORB is characterized by lower 206 Pb/ 204 Pb, hi...The isotopic signature of mid\|ocean ridge basalts (MORB) from the Indian Ocean is different from that of MORB from the Pacific and North\|Atlantic oceans.. The Indian MORB is characterized by lower 206 Pb/ 204 Pb, hi gher 87 Sr/ 86 Sr, and lower 206 Pb/ 204 Pb for given 143 Nd/ 144 Nd than the latter (Hart, 1984; Castillo, 1988; Mahoney et al., 1998). Why the Indian Ocean mantle domain is different from the Pacific and North\|Atlantic ocean mantle domain is still unclear. Two general classes of hypotheses have been proposed to explain the origin of Indian mantle (Mahoney et al., 1998). The first one is that the components of the Indian Ocean mantle domain are a fairly young mantle end\|member created during the processes of breakup of the Gondwana continent to form the Indian Ocean. The second hypothesis posits that the Indian MORB\|type isotopic signature is a long\|lived mantle domain that existed prior to the formation of the present Indian Ocean. Thus it appears that one of the keys to a better understanding of origin of the Indian Ocean\|type isotopic signature depends on its age. Although some studies (Mahoney et al., 1998; Weis and Frey, 1997) showed that the isotopic signature was as old as the Indian ocean crust (140Ma), basalts investigated in the Indian Ocean region do not prove or disprove the existence of the Indian MORB\|type isotopic signature prior to the Indian Ocean because they were taken from the Indian ocean basin itself.展开更多
Si-Fe-Mn-oxyhydroxides dredged at the PACMANUS （Papua New Guinea-Australia-Canada-Manus） hydrothermal field, Eastern Manus Basin, have 87Sr/SSSr=0.708 079-0.708 581; eNd=5.149 833-6.534 826; 208pb/204pb=38.245-38.44...Si-Fe-Mn-oxyhydroxides dredged at the PACMANUS （Papua New Guinea-Australia-Canada-Manus） hydrothermal field, Eastern Manus Basin, have 87Sr/SSSr=0.708 079-0.708 581; eNd=5.149 833-6.534 826; 208pb/204pb=38.245-38.440; 207pb/204pb=lS.503-15.560; 206pb/204pb=lS.682-18.783. s7sr/sSSr isotope ratios are relatively homogeneous and close to the value of the surrounding seawater （0.709 16）. The content of Sr in the samples contributed by seawater was estimated to be 76.7%-83.1% of total amount. The mixing temperature of hydrothermal fluids and seawater were ranging from 53.2℃ to 72.2℃ and the hydrothermal activities were unstable when the samples precipitated. The eNd values of all the samples are positive, which differ from the values of ferromanganese nodules （crusts） with hydrogenic origin. Nd was mainly derived from substrate rocks leached by hydrothermal circulation and preserved the hydrothermal signature. Ph isotopic compositions of most samples show minor variability except Sample #9-2 that has relatively high values of Pb isotopes. The Pb may be derived from the Eastern Manus Basin rocks leached by the hydrothermal fluid. The slightly lower 28pb/204pb and 207pb/204pb values of the samples indicated that the hydrothermal circulation in PACMANUS was not entire and sufficient, or that hydrothermal circulation had transient changes in the past. Si-Fe-Mn-oxyhydroxides in the samples preserved the heterogeneities of local rocks.展开更多
Uliramafie xenoliths provide an important constraint on the composition,strueture and evolution of the lithosphere mantle beneath eastern China. Most of the xenoliths entrained by the Cenzoic basalts have de pleted Sr...Uliramafie xenoliths provide an important constraint on the composition,strueture and evolution of the lithosphere mantle beneath eastern China. Most of the xenoliths entrained by the Cenzoic basalts have de pleted Sr and Nd isotopie composition. Interestingly evidences have been found for old ehriehed lithosphere mantle beneath thick Arehaean and post-Arehaean erust (＞35 km ) and for relatively homogeneous and depleted lithosphere mantle bencath thin erust (＜ 35 km ). Furthermore the chemieal composition of the lithosphere mantle is overall fertile regardless of the age of the overlying erust. The spatial variability in ehemieal and Sr and Nd isotopie eompositions of the ultramafie xenoliths in relation to the lithospherie ages and geometry implies a mixture strueture of the lithosphere mantle beheath easiern China. which consists of recently aecreted asthenospherie diapirs and old modified remnants. Isotopie eomposition of the Cenozoie basalts show obvious similarities with ocein island basalt (OIH ). We argue that enriehed lithosphere mantle delamineted during Mesozoic-Cenozoie tectonie-thermal events was generally involved in the Cenozoie basaltic voleanism.展开更多
The Mesozoic volcanic rocks in the coastal region of southeastern China were superimposed on some different basement tectonic elements. The volcanic rocks developed in these different basement tectonic elements have g...The Mesozoic volcanic rocks in the coastal region of southeastern China were superimposed on some different basement tectonic elements. The volcanic rocks developed in these different basement tectonic elements have great differences in Sr and Nd isotopic compositions. The rocks in western Zhejiang and northeastern Jiangxi Provinces which belong to the Lower Yangtze subplate have lower initial 87Sr/ 86Sr ratios, but are higher in initial Nd isotopic ratios. The initial 143Nd / 144Nd values of the volcanic rocks developed in the Cathaysian subplate increase clearly from early to late in time, and from the core of the Wuyishan uplift coastwards constantly, but the initial 87Sr/86Sr values tend to decrease. The isotopic characteristics and their spatial variations in Mesozoic volcanic rocks in the study region are, to a great extent, manifestations of the isotopic characteristics in basement metamorphic complexes, and the generation of the Mesozoic acid magma in this region is attributed to the recycling of pre-existing crustal materials.展开更多
基金supported by the Chinese Ministry of Science and Technology(Sinoprobe-05-03)Doctoral Fund of Ministry of Education of China(20110022120003)+1 种基金the Fundamental Research Funds for the Central UniversitiesOpen Fund of State Key Laboratory of Geological Processes and Mineral Resources(GPMR2011)
文摘Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period. Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma＇anshan area. Different samples within one eruption show relative identical lithologies, chemical and isotopic compositions. However, the geochemical features for the five eruptions are distinct from each other. These volcanic rocks show low Mg# values （〈45）, moderate to high fractionation of LREEs and HREEs, and enrichment of Pb and Ba and depletion of Nb. Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies. And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks. Segregated primitive magma pulsating injected into magma chamber, fractional crystallized and contaminated with crust component. Finally, magmas with distinct chemical and isotopic compositions for each eruption formed. The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.
基金The project supported by the State Antarctic Committeethe National Natural Science Foundation of China
文摘Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd-87Sr/86Sr, 87Sr/86Sr-Sr and 87Sr/86Sr-K2O/(K2O+Na2O) indicated that the volcanic rocks were chiefly derived from the depleted mantle source and generally were not mixed crust materials. Of the samples 6 were given the mean Sm -Nd model age (TDM) of 443. 3±20. 6 Ma possibly indicating the age of chemical variation event in the magma source of the study area. Features of the trace elements indicated that the rocks from the Half Three Point Formation are of typical calc-alkaline volcanic suite and similar to those from the Tertiary volcanic rocks of the Fildes Peninsula, being the same products of the island-arc volcanic activity.
文摘Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr),=0.70895-0.71140) and low (143Nd/144Nd)1 ratios (varying from 0.51135 to 0.51231); and its δ18Osmow, whole rock values vary from +5.8%c to +10.6%c with a mean of +7.1%c. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced metasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enriched mantle in its mature stage in the back-arc spreading environment. The evolution of magmas is associated with two trends, i.e., fractional crystallization and mixing with or intensive contamination by palaeo-crust materials or metamorphic rocks. The former process is evident in the gold field system of quartz-vein type, whereas the latter is dominated in the gold field system of the altered-rock type. This conclusion is very important for more detailed study of petrogenesis and mineralization through the crust-mantle interaction (exchange) in the Mesozoic in this region.
文摘The isotopic signature of mid\|ocean ridge basalts (MORB) from the Indian Ocean is different from that of MORB from the Pacific and North\|Atlantic oceans.. The Indian MORB is characterized by lower 206 Pb/ 204 Pb, hi gher 87 Sr/ 86 Sr, and lower 206 Pb/ 204 Pb for given 143 Nd/ 144 Nd than the latter (Hart, 1984; Castillo, 1988; Mahoney et al., 1998). Why the Indian Ocean mantle domain is different from the Pacific and North\|Atlantic ocean mantle domain is still unclear. Two general classes of hypotheses have been proposed to explain the origin of Indian mantle (Mahoney et al., 1998). The first one is that the components of the Indian Ocean mantle domain are a fairly young mantle end\|member created during the processes of breakup of the Gondwana continent to form the Indian Ocean. The second hypothesis posits that the Indian MORB\|type isotopic signature is a long\|lived mantle domain that existed prior to the formation of the present Indian Ocean. Thus it appears that one of the keys to a better understanding of origin of the Indian Ocean\|type isotopic signature depends on its age. Although some studies (Mahoney et al., 1998; Weis and Frey, 1997) showed that the isotopic signature was as old as the Indian ocean crust (140Ma), basalts investigated in the Indian Ocean region do not prove or disprove the existence of the Indian MORB\|type isotopic signature prior to the Indian Ocean because they were taken from the Indian ocean basin itself.
基金The National Key Basic Research Program of China under contract No.2013CB429700the National Special Fund for the 12th Five Year Plan of COMRA under contract No.DY125-12-R-05+3 种基金the National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02 and DY125-11-R-05the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11030302the National Natural Science Foundation of China under contract Nos 41325021,40830849 and 40976027Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract No.JQ200913
文摘Si-Fe-Mn-oxyhydroxides dredged at the PACMANUS （Papua New Guinea-Australia-Canada-Manus） hydrothermal field, Eastern Manus Basin, have 87Sr/SSSr=0.708 079-0.708 581; eNd=5.149 833-6.534 826; 208pb/204pb=38.245-38.440; 207pb/204pb=lS.503-15.560; 206pb/204pb=lS.682-18.783. s7sr/sSSr isotope ratios are relatively homogeneous and close to the value of the surrounding seawater （0.709 16）. The content of Sr in the samples contributed by seawater was estimated to be 76.7%-83.1% of total amount. The mixing temperature of hydrothermal fluids and seawater were ranging from 53.2℃ to 72.2℃ and the hydrothermal activities were unstable when the samples precipitated. The eNd values of all the samples are positive, which differ from the values of ferromanganese nodules （crusts） with hydrogenic origin. Nd was mainly derived from substrate rocks leached by hydrothermal circulation and preserved the hydrothermal signature. Ph isotopic compositions of most samples show minor variability except Sample #9-2 that has relatively high values of Pb isotopes. The Pb may be derived from the Eastern Manus Basin rocks leached by the hydrothermal fluid. The slightly lower 28pb/204pb and 207pb/204pb values of the samples indicated that the hydrothermal circulation in PACMANUS was not entire and sufficient, or that hydrothermal circulation had transient changes in the past. Si-Fe-Mn-oxyhydroxides in the samples preserved the heterogeneities of local rocks.
文摘Uliramafie xenoliths provide an important constraint on the composition,strueture and evolution of the lithosphere mantle beneath eastern China. Most of the xenoliths entrained by the Cenzoic basalts have de pleted Sr and Nd isotopie composition. Interestingly evidences have been found for old ehriehed lithosphere mantle beneath thick Arehaean and post-Arehaean erust (＞35 km ) and for relatively homogeneous and depleted lithosphere mantle bencath thin erust (＜ 35 km ). Furthermore the chemieal composition of the lithosphere mantle is overall fertile regardless of the age of the overlying erust. The spatial variability in ehemieal and Sr and Nd isotopie eompositions of the ultramafie xenoliths in relation to the lithospherie ages and geometry implies a mixture strueture of the lithosphere mantle beheath easiern China. which consists of recently aecreted asthenospherie diapirs and old modified remnants. Isotopie eomposition of the Cenozoie basalts show obvious similarities with ocein island basalt (OIH ). We argue that enriehed lithosphere mantle delamineted during Mesozoic-Cenozoie tectonie-thermal events was generally involved in the Cenozoie basaltic voleanism.
基金This paper resulted from the joint support of the National Natural Science Foundation of China (Grant No. 49070162)a key project of the Ministry of Geology and Mineral Resources for the Seventh Five-Year Plan period (Project No. 86017)
文摘The Mesozoic volcanic rocks in the coastal region of southeastern China were superimposed on some different basement tectonic elements. The volcanic rocks developed in these different basement tectonic elements have great differences in Sr and Nd isotopic compositions. The rocks in western Zhejiang and northeastern Jiangxi Provinces which belong to the Lower Yangtze subplate have lower initial 87Sr/ 86Sr ratios, but are higher in initial Nd isotopic ratios. The initial 143Nd / 144Nd values of the volcanic rocks developed in the Cathaysian subplate increase clearly from early to late in time, and from the core of the Wuyishan uplift coastwards constantly, but the initial 87Sr/86Sr values tend to decrease. The isotopic characteristics and their spatial variations in Mesozoic volcanic rocks in the study region are, to a great extent, manifestations of the isotopic characteristics in basement metamorphic complexes, and the generation of the Mesozoic acid magma in this region is attributed to the recycling of pre-existing crustal materials.
