The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO<sub>2</sub> and low K<s...The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO<sub>2</sub> and low K<sub>2</sub>O,and depletion of light rare earth elements.They should be originated from a depleted asthenosphere mantle, belonging to ancient oceanic crust ophiolitic volcanic rock association.Compared with the Longba tholeiitic basalt,the Ganlongtang tholeiitic basalt shows展开更多
The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep wate...The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .展开更多
The Nantinghe ophiolite is located in the northern part of the Changning-Menglian suture zone in southeast Tibet. It is composed of meta-peridotite, cumulative gabbro, meta-gabbro, plagioclase amphibolite and meta-bas...The Nantinghe ophiolite is located in the northern part of the Changning-Menglian suture zone in southeast Tibet. It is composed of meta-peridotite, cumulative gabbro, meta-gabbro, plagioclase amphibolite and meta-basalt. Zircon U-Pb dating of the cumulative gabbro gives concordant ages of 473.0±3.8 Ma and 443.6±4.0 Ma respectively, indicating the early and late episodes of mafic magmatisms during the Paleo-Tethys oceanic rifting. The 16 LA-ICPMS zircon U-Pb analyses of meta-gabbro yield a weight mean age of 439±2.4Ma. The gabbro shows relatively low contents of SiO2 (46.46%-52.11%), TiO2 (0.96%-1.14%) and K2O (0.48%-0.75%). Its trace element distribution patterns are partly similar to those of the mid-ocean ridge basalts, and part is depleted in high field strength elements such as Nb, Ta, Zr, Hf and Ti. These features suggest that the mafic rocks were probably formed in a MORB-like or backarc rift basin setting. The zircon U-Pb age of gabbro is consistent with a late crystallization age of the cumulative gabbro from the Nantinghe ophiolite, suggesting that the Paleo-Tethys oceanic basin was opened during 444-439 Ma, possibly as a backarc basin. It is the first precise age which defines the formation time of the early Paleozoic ophiolite in the Changning-Menglian suture zone. These geochronological and geochemical characteristics of the Nantinghe ophiolite are consistent with those from the Guoganjianianshan and Taoxinghu of the Longmu Co-Shuanghu suture in the Qiangtang region. Thus, we suggest that the both Changning-Menglian and Longmu Co-Shuanghu sutures were probably transformed from the relic oceanic crust of the uniform Paleo-Tethys, which likely represents the original and main Paleo-Tethys oceanic basin.展开更多
The oceanic island volcanic rocks in the Chiang Mai zone, northern Thailand, are usually covered by Lower Carboniferous and Upper Permian shallow-water carbonate rocks, with the Hawaii rocks and potash trachybasalt be...The oceanic island volcanic rocks in the Chiang Mai zone, northern Thailand, are usually covered by Lower Carboniferous and Upper Permian shallow-water carbonate rocks, with the Hawaii rocks and potash trachybasalt being the main rock types. The alkaline series is dominant with sub-alkaline series occurring in few cases. The geochemical characteristics are described as follows: the major chemical compositions are characterized by high TiO2, high P2O5 and medium K2O; the rare-earth elements are characterized by right-inclined strong LREE-enrichment patterns; the trace element patterns are of the upward-bulging K-Ti enrichment type; multi-component plots falling within the fields of oceanic island basalts and alkali basalts, belonging to the oceanic island-type volcanic rocks, which are similar to the equivalents in Deqin and Gengma (the Changning-Menglian zone) of Yunnan Province, China.展开更多
文摘The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO<sub>2</sub> and low K<sub>2</sub>O,and depletion of light rare earth elements.They should be originated from a depleted asthenosphere mantle, belonging to ancient oceanic crust ophiolitic volcanic rock association.Compared with the Longba tholeiitic basalt,the Ganlongtang tholeiitic basalt shows
文摘The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .
基金supported by the National Basic Research Program of China (2009CB421003)the National Natural Science Foundation of China (41073033 and 40872055)the Chinese Geological Survey Projects (1212011121259 and 1212011085119)
文摘The Nantinghe ophiolite is located in the northern part of the Changning-Menglian suture zone in southeast Tibet. It is composed of meta-peridotite, cumulative gabbro, meta-gabbro, plagioclase amphibolite and meta-basalt. Zircon U-Pb dating of the cumulative gabbro gives concordant ages of 473.0±3.8 Ma and 443.6±4.0 Ma respectively, indicating the early and late episodes of mafic magmatisms during the Paleo-Tethys oceanic rifting. The 16 LA-ICPMS zircon U-Pb analyses of meta-gabbro yield a weight mean age of 439±2.4Ma. The gabbro shows relatively low contents of SiO2 (46.46%-52.11%), TiO2 (0.96%-1.14%) and K2O (0.48%-0.75%). Its trace element distribution patterns are partly similar to those of the mid-ocean ridge basalts, and part is depleted in high field strength elements such as Nb, Ta, Zr, Hf and Ti. These features suggest that the mafic rocks were probably formed in a MORB-like or backarc rift basin setting. The zircon U-Pb age of gabbro is consistent with a late crystallization age of the cumulative gabbro from the Nantinghe ophiolite, suggesting that the Paleo-Tethys oceanic basin was opened during 444-439 Ma, possibly as a backarc basin. It is the first precise age which defines the formation time of the early Paleozoic ophiolite in the Changning-Menglian suture zone. These geochronological and geochemical characteristics of the Nantinghe ophiolite are consistent with those from the Guoganjianianshan and Taoxinghu of the Longmu Co-Shuanghu suture in the Qiangtang region. Thus, we suggest that the both Changning-Menglian and Longmu Co-Shuanghu sutures were probably transformed from the relic oceanic crust of the uniform Paleo-Tethys, which likely represents the original and main Paleo-Tethys oceanic basin.
基金granted by the National Natural Science Foundation of China (Grant Nos. 40372105 and 40772143)
文摘The oceanic island volcanic rocks in the Chiang Mai zone, northern Thailand, are usually covered by Lower Carboniferous and Upper Permian shallow-water carbonate rocks, with the Hawaii rocks and potash trachybasalt being the main rock types. The alkaline series is dominant with sub-alkaline series occurring in few cases. The geochemical characteristics are described as follows: the major chemical compositions are characterized by high TiO2, high P2O5 and medium K2O; the rare-earth elements are characterized by right-inclined strong LREE-enrichment patterns; the trace element patterns are of the upward-bulging K-Ti enrichment type; multi-component plots falling within the fields of oceanic island basalts and alkali basalts, belonging to the oceanic island-type volcanic rocks, which are similar to the equivalents in Deqin and Gengma (the Changning-Menglian zone) of Yunnan Province, China.
