Field investigations and laboratory integrated research as indicated that ophiolite mélange in the Nan-Uttaradit zone, northern Thailand, consists of fragments of tectonites such as metamorphic peridotite (extrem...Field investigations and laboratory integrated research as indicated that ophiolite mélange in the Nan-Uttaradit zone, northern Thailand, consists of fragments of tectonites such as metamorphic peridotite (extremely silicified serpentinite), cumulates (pyroxenolite, gabbro, and gabbro-diorite), ocean-ridge basalt, oceanic-island ba-salt and radiolarian silicalite, and it was formed during D3-P. The rock series, rock types and petrogeochemical characteristics of metamorphic tholeiites in the Nan area of the Nan-Uttaradit zone are similar to those of ocean-ridge basalts (C1) in China's Ailaoshan zone. As for the Hawaiites in the Nan area of the Nan-Uttaradit zone, their major elements, REEs and trace elements are similar to those of oceanic-island basalts in China's Jinshanjiang zone (P11). In the Uttaradit area of this zone the metamorphic alkaline basalts show transitional petrogeochemical characteristics between ocean-ridge basalts and oceanic-island basalts, which were still formed in oceanic-island environments. The above-described basalts are all oceanic volcanic rocks and they are the most important part of the Paleo-Tethys oceanic crust in the Nan-Uttaradit zone.展开更多
Late Permian-Early Triassic(P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics,rock ass...Late Permian-Early Triassic(P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics,rock assemblage,REE,trace elements,geotectonic setting,etc.,indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks.The volcanic rock assemblage is basalt-basaltic andesite-andesite.The volcanic rocks are sub-alkaline,dominated by calc-alkaline series,with tholeiite series coming next.The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O.Their REE patterns are of the flat,weak LREE-enrichment right-inclined type.The trace elements are characterized by the enrichment of large cation elements such as K,Rb and Ba,common enrichment of U and Th,and depletion of Nb,Ta,Zr and Hf.The petrochemical plot falls within the field of volcanic rocks,in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China.This island-arc volcanic zone,together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone,constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs,indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction.This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.展开更多
The environmental conditions and the biotic crisis during the Permo-Triassic (Tr/P) transition received increasing attention in the past decades. Presented herein are the molecular fossil records of cyano-bacteria and...The environmental conditions and the biotic crisis during the Permo-Triassic (Tr/P) transition received increasing attention in the past decades. Presented herein are the molecular fossil records of cyano-bacteria and green sulfur bacteria,the base of the marine ecosystem,to highlight the episodic nature of both the environment and the biotic crisis during this critical period. At least two episodes of cyano-bacterial expansion are documented by 2-methylhopanes ranging from C28 to C32 in carbon number,indicative of the instable marine ecosystem and the fluctuant aquatic nutrients. Meanwhile,the index of 2-alkyl-1,3,4-trimethylbenzenes (biomarkers of green sulfur bacteria) and the ratio of pristane to phy-tane (Pr/Ph) witness the fluctuation of sedimentary environmental redox conditions. The above mo-lecular evidence suggests the occurrence of highly fluctuating environmental conditions during the Tr/P transition,which is consistent with,and probably the cause of,the multi-phased biotic crisis and the prolonged faunal recovery.展开更多
基金by the National Natural Science Foundation of China(Grant Nos. 40372105 and 40772143)
文摘Field investigations and laboratory integrated research as indicated that ophiolite mélange in the Nan-Uttaradit zone, northern Thailand, consists of fragments of tectonites such as metamorphic peridotite (extremely silicified serpentinite), cumulates (pyroxenolite, gabbro, and gabbro-diorite), ocean-ridge basalt, oceanic-island ba-salt and radiolarian silicalite, and it was formed during D3-P. The rock series, rock types and petrogeochemical characteristics of metamorphic tholeiites in the Nan area of the Nan-Uttaradit zone are similar to those of ocean-ridge basalts (C1) in China's Ailaoshan zone. As for the Hawaiites in the Nan area of the Nan-Uttaradit zone, their major elements, REEs and trace elements are similar to those of oceanic-island basalts in China's Jinshanjiang zone (P11). In the Uttaradit area of this zone the metamorphic alkaline basalts show transitional petrogeochemical characteristics between ocean-ridge basalts and oceanic-island basalts, which were still formed in oceanic-island environments. The above-described basalts are all oceanic volcanic rocks and they are the most important part of the Paleo-Tethys oceanic crust in the Nan-Uttaradit zone.
基金the National Natural Science Foundation of China (Grant Nos. 40372105 and 40772143)
文摘Late Permian-Early Triassic(P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics,rock assemblage,REE,trace elements,geotectonic setting,etc.,indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks.The volcanic rock assemblage is basalt-basaltic andesite-andesite.The volcanic rocks are sub-alkaline,dominated by calc-alkaline series,with tholeiite series coming next.The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O.Their REE patterns are of the flat,weak LREE-enrichment right-inclined type.The trace elements are characterized by the enrichment of large cation elements such as K,Rb and Ba,common enrichment of U and Th,and depletion of Nb,Ta,Zr and Hf.The petrochemical plot falls within the field of volcanic rocks,in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China.This island-arc volcanic zone,together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone,constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs,indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction.This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.
基金Supported by the National Natural Science Foundation of China (Grant Nos.40525008 and 40232025)NCET Program of Ministry of Education of China (Grant No. NCET-04-0729)Fok Ying Tung Education Foundation
文摘The environmental conditions and the biotic crisis during the Permo-Triassic (Tr/P) transition received increasing attention in the past decades. Presented herein are the molecular fossil records of cyano-bacteria and green sulfur bacteria,the base of the marine ecosystem,to highlight the episodic nature of both the environment and the biotic crisis during this critical period. At least two episodes of cyano-bacterial expansion are documented by 2-methylhopanes ranging from C28 to C32 in carbon number,indicative of the instable marine ecosystem and the fluctuant aquatic nutrients. Meanwhile,the index of 2-alkyl-1,3,4-trimethylbenzenes (biomarkers of green sulfur bacteria) and the ratio of pristane to phy-tane (Pr/Ph) witness the fluctuation of sedimentary environmental redox conditions. The above mo-lecular evidence suggests the occurrence of highly fluctuating environmental conditions during the Tr/P transition,which is consistent with,and probably the cause of,the multi-phased biotic crisis and the prolonged faunal recovery.
