Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice, dacite, etc. Inclusions in the minerals of the volcanic rocks are main-ly amorphous melt i...Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice, dacite, etc. Inclusions in the minerals of the volcanic rocks are main-ly amorphous melt inclusions, Which reflects that the volcanic rocks are characterized by submarine eruption and rapid cooling on the seafloor. Furthermore, fluid-melt inclusions have been discovered for the first time in alkali basalts and mantle-derived xenoliths, indicating a process of differentiation between magma and fluid in the course of mantle partial melting. Alkali basalts and inclusions may have been formed in this nonhomogeneous system.Rock-forming temperatures of four seamounts were estimated as follows: the Zhongnan seamount alkali basalt 1155 ～1185 ℃, the Xianbei seamount alkali basalt 960～1200℃, tholeiitic basalt 1040～1230℃, the Daimao seamount tholeiitic basalt 1245 ～1280℃; and the Jianfeng seamount trachyandestic pumice 880～1140℃. Equilibrium pressures of alkali basalts in the Zhongnan and Xanbei seamounts are 13.57 and 8.8 × 108 Pa, respectively. Pyroxene equilibrium tem-peratures of mantle xenoliths from the Xianbei seamount were estimated at 1073～1121℃, and pres-sures at (15.58 ～ 22.47)× 108Pa, suggesting a deep-source (e.g. the asthenosphere) for the alkali basalts.展开更多
The well-preserved seamount buildups are documented from the northwestern Qinling （秦岭） orogenic belts, Northwest China. The study sections are located in the Ganjia （甘加） area of the Xiahe （夏河） County, Gan...The well-preserved seamount buildups are documented from the northwestern Qinling （秦岭） orogenic belts, Northwest China. The study sections are located in the Ganjia （甘加） area of the Xiahe （夏河） County, Gansu （甘肃） Province. The dark basalt and overlying massive reef carbonate characterize the Xiahe seamount buildup. Basalts are dominated by the olivine type of rocks and bear distinct porphyritic textures, and fumarole and amygdaloidal structures. The basalts are dominated by SiO2 （up to 48.49 wt.%-52.29 wt.%） followed by （Na2O＋ K2O） （3.80 wt.%-4.96 wt.%） and TiO2 （2.04 wt.%-2.52 wt.%）. They are featured by considerably high content of Ti. The tholeiiteseries rocks dominate the basalts, while calc-alkali-series rocks are also present. The REE of the basalts shows the LREE-enrichment type with distinct positive Eu abnormal. The trace elements of the basalts are characterized by the lack of P and high content of Ti. These geochemical signals suggest that the Xiahe basalts were formed in an ocean-island setting. The LA ICP-MS zircon U-Pb age of the basalts is 267.6±5 Ma, which is reinforced by the presnce of the fusulinid Neoschwagerina Zone of the Wordian （Middle Permian） in the limestone interbeds of the basalts. Integration of petrological and geochemical studies of seamount basalts and lateral correlation of seamount buildups reveals that the Qinling-Qilian-Kunlun orogenic belts were probably the archipelagic oceans during the Permian.展开更多
The widespread Permian carbonate strata outcropped in northwestern Thailand are considered as the evidence for the Late Paleozoic shallow Tethys. Our investigation, however, shows that basalt can be discovered usually...The widespread Permian carbonate strata outcropped in northwestern Thailand are considered as the evidence for the Late Paleozoic shallow Tethys. Our investigation, however, shows that basalt can be discovered usually under the Permian carbonate sequence in Chiang Mai-Fang area, northwestern Thailand. The basalt belongs to subalkalic basalt and potassic trachybasalt. They are characterized by high P and Ti in major elements, by high content, enriching LREE, lacking δEu anomaly in rare earth elements, and by enrichment of the large ion lithophile element (LILE) (K, Rb, Ba) and high field strength element (HFSE) (Nb, Ta, Zr) in trace elements, which can be compared with the characters of the oceanic island basalt in Three Rivers (Jinsha River, Lancang River, and Nujiang River) area, southwestern China. Therefore, the Permian carbonate in the studied area was deposited on a sea-mount, rather than on a stable carbonate platform. The oceanic basin is correlated to the Late Paleozoic ocean represented by the Changning-Menglian Belt in southwestern China and they are a major basin of the Paleo-Tethyan Archipelagoes Ocean. The result indicates nonexistence of a Shan-Thai Block in the Late Paleozoic.展开更多
The Changning-Menglian suture in SW Yunnan has been accepted as the Paleotethyan main ocean. However, it has been a matter of debate as to its southerly extension in NW Thailand（the Chiang Mai-Chiang Rai vs. Nan-Utta...The Changning-Menglian suture in SW Yunnan has been accepted as the Paleotethyan main ocean. However, it has been a matter of debate as to its southerly extension in NW Thailand（the Chiang Mai-Chiang Rai vs. Nan-Uttaradit zone）. Our field investigation identified the high-iron basaltic rocks in the Chiang Dao Permian standard profile in NW Thailand. The high-iron rocks provide crucial records for understanding the controversy on the location of Paleotethyan main ocean in NW Thailand. The Early Permian high-iron samples show extremely high Fe Ot（20.96 wt.%–25.56 wt.%） and TiO2（6.07 wt.%–6.34 wt.%） and low SiO2（38.54 wt.%–43.46 wt.%） and Mg O（1.61 wt.%–2.40 wt.%） contents. Such characteristics are similar to those of the Fenner differentiation trend rarely observed in the natural system, distinct from those of the ＂normal＂ Bowen trend. Their chondrite- normalized REE and primitive mantle-normalized patterns are generally similar to those of typical OIB. The initial 87Sr/86 Sr ratios and εNd（t） values range from 0.704 677 to 0.705 103 and 3.16 to 3.48, respectively, falling near the field of typical OIB（oceanic-island basalt）. These data synthetically suggest that the Chiang Dao high-iron rocks are the products of high-degree partial melting of peridotite with Fe-rich eclogitic blobs/streaks in response to a seamount setting. In comparison with the Permian tectonic setting in SW Yunnan and NW Thailand, it is inferred that the Paleotethyan Ocean was located between the Shan-Thai terrane of Sibumasu and Sukhothai arc along the Inthanon zone of the Chiang Mai-Chiang Rai rather than Nan-Uttaradit zones.展开更多
文摘Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice, dacite, etc. Inclusions in the minerals of the volcanic rocks are main-ly amorphous melt inclusions, Which reflects that the volcanic rocks are characterized by submarine eruption and rapid cooling on the seafloor. Furthermore, fluid-melt inclusions have been discovered for the first time in alkali basalts and mantle-derived xenoliths, indicating a process of differentiation between magma and fluid in the course of mantle partial melting. Alkali basalts and inclusions may have been formed in this nonhomogeneous system.Rock-forming temperatures of four seamounts were estimated as follows: the Zhongnan seamount alkali basalt 1155 ～1185 ℃, the Xianbei seamount alkali basalt 960～1200℃, tholeiitic basalt 1040～1230℃, the Daimao seamount tholeiitic basalt 1245 ～1280℃; and the Jianfeng seamount trachyandestic pumice 880～1140℃. Equilibrium pressures of alkali basalts in the Zhongnan and Xanbei seamounts are 13.57 and 8.8 × 108 Pa, respectively. Pyroxene equilibrium tem-peratures of mantle xenoliths from the Xianbei seamount were estimated at 1073～1121℃, and pres-sures at (15.58 ～ 22.47)× 108Pa, suggesting a deep-source (e.g. the asthenosphere) for the alkali basalts.
基金supported by the MOST Special Fund of the State Key Laboratory of Geological Processes and Mineral Resources, the Special Fund for the National Excellent Dissertation for Doctor Degree (No. 200228)the Foundation of China Geological Survey (No. 200413000007)+1 种基金the National Natural Science Foundation of China (No. 40621002)the Fund of the Important Mineral Forming Geological Setting from the Ministry of Land and Resources (No. 1212010733802)
文摘The well-preserved seamount buildups are documented from the northwestern Qinling （秦岭） orogenic belts, Northwest China. The study sections are located in the Ganjia （甘加） area of the Xiahe （夏河） County, Gansu （甘肃） Province. The dark basalt and overlying massive reef carbonate characterize the Xiahe seamount buildup. Basalts are dominated by the olivine type of rocks and bear distinct porphyritic textures, and fumarole and amygdaloidal structures. The basalts are dominated by SiO2 （up to 48.49 wt.%-52.29 wt.%） followed by （Na2O＋ K2O） （3.80 wt.%-4.96 wt.%） and TiO2 （2.04 wt.%-2.52 wt.%）. They are featured by considerably high content of Ti. The tholeiiteseries rocks dominate the basalts, while calc-alkali-series rocks are also present. The REE of the basalts shows the LREE-enrichment type with distinct positive Eu abnormal. The trace elements of the basalts are characterized by the lack of P and high content of Ti. These geochemical signals suggest that the Xiahe basalts were formed in an ocean-island setting. The LA ICP-MS zircon U-Pb age of the basalts is 267.6±5 Ma, which is reinforced by the presnce of the fusulinid Neoschwagerina Zone of the Wordian （Middle Permian） in the limestone interbeds of the basalts. Integration of petrological and geochemical studies of seamount basalts and lateral correlation of seamount buildups reveals that the Qinling-Qilian-Kunlun orogenic belts were probably the archipelagic oceans during the Permian.
基金the National Natural Science Foundation of China (Grant Nos.40372105,40772143)"111" Project (Grant No. B08030)Suranaree University of Technology, Thailand
文摘The widespread Permian carbonate strata outcropped in northwestern Thailand are considered as the evidence for the Late Paleozoic shallow Tethys. Our investigation, however, shows that basalt can be discovered usually under the Permian carbonate sequence in Chiang Mai-Fang area, northwestern Thailand. The basalt belongs to subalkalic basalt and potassic trachybasalt. They are characterized by high P and Ti in major elements, by high content, enriching LREE, lacking δEu anomaly in rare earth elements, and by enrichment of the large ion lithophile element (LILE) (K, Rb, Ba) and high field strength element (HFSE) (Nb, Ta, Zr) in trace elements, which can be compared with the characters of the oceanic island basalt in Three Rivers (Jinsha River, Lancang River, and Nujiang River) area, southwestern China. Therefore, the Permian carbonate in the studied area was deposited on a sea-mount, rather than on a stable carbonate platform. The oceanic basin is correlated to the Late Paleozoic ocean represented by the Changning-Menglian Belt in southwestern China and they are a major basin of the Paleo-Tethyan Archipelagoes Ocean. The result indicates nonexistence of a Shan-Thai Block in the Late Paleozoic.
基金Financial supports from the National Natural Science Foundation of China(Nos.41190073 and 41402165the Fundamental Research Funds for the Central Universities to SYSU are gratefully acknowledged
文摘The Changning-Menglian suture in SW Yunnan has been accepted as the Paleotethyan main ocean. However, it has been a matter of debate as to its southerly extension in NW Thailand（the Chiang Mai-Chiang Rai vs. Nan-Uttaradit zone）. Our field investigation identified the high-iron basaltic rocks in the Chiang Dao Permian standard profile in NW Thailand. The high-iron rocks provide crucial records for understanding the controversy on the location of Paleotethyan main ocean in NW Thailand. The Early Permian high-iron samples show extremely high Fe Ot（20.96 wt.%–25.56 wt.%） and TiO2（6.07 wt.%–6.34 wt.%） and low SiO2（38.54 wt.%–43.46 wt.%） and Mg O（1.61 wt.%–2.40 wt.%） contents. Such characteristics are similar to those of the Fenner differentiation trend rarely observed in the natural system, distinct from those of the ＂normal＂ Bowen trend. Their chondrite- normalized REE and primitive mantle-normalized patterns are generally similar to those of typical OIB. The initial 87Sr/86 Sr ratios and εNd（t） values range from 0.704 677 to 0.705 103 and 3.16 to 3.48, respectively, falling near the field of typical OIB（oceanic-island basalt）. These data synthetically suggest that the Chiang Dao high-iron rocks are the products of high-degree partial melting of peridotite with Fe-rich eclogitic blobs/streaks in response to a seamount setting. In comparison with the Permian tectonic setting in SW Yunnan and NW Thailand, it is inferred that the Paleotethyan Ocean was located between the Shan-Thai terrane of Sibumasu and Sukhothai arc along the Inthanon zone of the Chiang Mai-Chiang Rai rather than Nan-Uttaradit zones.
