Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks...Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that the rocks are characterized by SiO2>59%, enrichment in A12O3(15.09-15.64%) and Na2O (>3.6%), high Sr (649-885 μg/g) and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg<0.35), weak Eu anomaly (Eu/Eu=0.84-0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd and Sr isotope data (87Sr/86Sr=0.7062-0.7079, 143Nd/144Nd=0.51166-0.51253, εNd= -18.61-0.02), show that the magma resulted from partial melting (10%-40%) of newly underplated basaltic lower crust under high pressure (1-4 GPa), and the petrogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will give an insight into the uplift mechanism of the Tibetan plateau.展开更多
The Kyaukmyet prospect lies approximately 5 km ENE of the high-sulfidation Kyisintaung copper-gold deposit,Monywa district,central Myanmar.Geologically,the research area is remarked by magmatic extrusion that occurred...The Kyaukmyet prospect lies approximately 5 km ENE of the high-sulfidation Kyisintaung copper-gold deposit,Monywa district,central Myanmar.Geologically,the research area is remarked by magmatic extrusion that occurred during the Late Oligocene to Middle Miocene of Magyigon Formation which led to the outcrops of volcanic rocks.Study detailed on petrographical and geochemical of the Kyaukmyet volcanic rocks has not been performed before the present work.The principal aim of this paper is to document the petrographical and geochemical characteristics of volcanic suite rocks exposed in the Kyaukmyet prospect.The results of this data have provided insight into the origin of the rocks and petrogenetic processes during evolution.Petrographically,all the studied volcanic rocks in the research area show that trachytic and porphyritic textures with phenocrysts of quartz,plagioclase,and K-feldspar which are embedded in a fine to medium grained groundmass.The accessory minerals of this rock consist of biotite,chlorite and opaque mineral.Geochemically,these volcanic rocks having calc-alkaline nature and classified as volcanic field(rhyolite)as well as volcanic arc setting.Based on the chondrite normalized spider diagram,LREE has enriched to HREE in this area which indicated negative Eu anomaly and subduction tectonic setting.展开更多
Our two newly obtained high-quality 40Ar/39Ar ages suggest that the high-K volcanic rocks of the Lawuxiang Formation in the Mangkang basin, Tibet were formed at 33.5 ( 0.2 Ma. The tracing of elemental and Pb-Sr-Nd iso...Our two newly obtained high-quality 40Ar/39Ar ages suggest that the high-K volcanic rocks of the Lawuxiang Formation in the Mangkang basin, Tibet were formed at 33.5 ( 0.2 Ma. The tracing of elemental and Pb-Sr-Nd isotopic geochemistry indicates that they were derived from an EM2 enriched mantle in continental subduction caused by transpression. Their evidently negative anomalies in HFSEs such as Nb and Ta make clear that there is an input of continental material into the mantle source. The high-K rocks at 33.5 ( 0.2 Ma in the Mangkang basin may temporally, spatially and compositionally compare with the early one of two-pulse high-K rocks in eastern Tibet distinguished by Wang J. H. Et al., implying that they were formed in the same tectonic setting.展开更多
基金supported jointly by"the Ninth Five-Year Plan"key basic research program(Grant No.9501101-5)the Project of Knowledge Innovation sponsored by the Chinese Academy of Scienoes(Grant No.KZCX2-102the National Outstanding Young Scientists Fund Project(Grant No.49925309)
文摘Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that the rocks are characterized by SiO2>59%, enrichment in A12O3(15.09-15.64%) and Na2O (>3.6%), high Sr (649-885 μg/g) and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg<0.35), weak Eu anomaly (Eu/Eu=0.84-0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd and Sr isotope data (87Sr/86Sr=0.7062-0.7079, 143Nd/144Nd=0.51166-0.51253, εNd= -18.61-0.02), show that the magma resulted from partial melting (10%-40%) of newly underplated basaltic lower crust under high pressure (1-4 GPa), and the petrogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will give an insight into the uplift mechanism of the Tibetan plateau.
文摘The Kyaukmyet prospect lies approximately 5 km ENE of the high-sulfidation Kyisintaung copper-gold deposit,Monywa district,central Myanmar.Geologically,the research area is remarked by magmatic extrusion that occurred during the Late Oligocene to Middle Miocene of Magyigon Formation which led to the outcrops of volcanic rocks.Study detailed on petrographical and geochemical of the Kyaukmyet volcanic rocks has not been performed before the present work.The principal aim of this paper is to document the petrographical and geochemical characteristics of volcanic suite rocks exposed in the Kyaukmyet prospect.The results of this data have provided insight into the origin of the rocks and petrogenetic processes during evolution.Petrographically,all the studied volcanic rocks in the research area show that trachytic and porphyritic textures with phenocrysts of quartz,plagioclase,and K-feldspar which are embedded in a fine to medium grained groundmass.The accessory minerals of this rock consist of biotite,chlorite and opaque mineral.Geochemically,these volcanic rocks having calc-alkaline nature and classified as volcanic field(rhyolite)as well as volcanic arc setting.Based on the chondrite normalized spider diagram,LREE has enriched to HREE in this area which indicated negative Eu anomaly and subduction tectonic setting.
基金This work was jointly supported by the National Natural Science Foundation of China(Grant No.49972026)the Guangdong Natural Science Foundation(Grant No.990531)+1 种基金the project of the ChineseAcademy of Sciences(Grant No.KZCX2-SW-117)the Chinese National Key Project for Basic Research(Grant No.G1998040807)and US NSF.
文摘Our two newly obtained high-quality 40Ar/39Ar ages suggest that the high-K volcanic rocks of the Lawuxiang Formation in the Mangkang basin, Tibet were formed at 33.5 ( 0.2 Ma. The tracing of elemental and Pb-Sr-Nd isotopic geochemistry indicates that they were derived from an EM2 enriched mantle in continental subduction caused by transpression. Their evidently negative anomalies in HFSEs such as Nb and Ta make clear that there is an input of continental material into the mantle source. The high-K rocks at 33.5 ( 0.2 Ma in the Mangkang basin may temporally, spatially and compositionally compare with the early one of two-pulse high-K rocks in eastern Tibet distinguished by Wang J. H. Et al., implying that they were formed in the same tectonic setting.
