The development of a plateau is an integral part of the evolution of recent large orogens. This is suggested by the presence of wide regions of high topographic relief in many Phanerozoic collisional belts, with the T...The development of a plateau is an integral part of the evolution of recent large orogens. This is suggested by the presence of wide regions of high topographic relief in many Phanerozoic collisional belts, with the Tibetan, Anatolian, Altiplano and Colorado plateaus forming the most often cited examples. To date, plateaus have not been documented in Proterozoic orogens. However, if large Proterozoic convergent belts developed plateaus, evidence should be preserved in the geologic record.Proterozoic belts expose deeper crustal levels that are not directly accessible in modern analogues. Therefore, if they represent the final product of a plateau style evolution, their study may give direct insight on the nature of the middle to lower crust beneath modern orogenic plateaus. The Grenville Province of the Canadian Shield is a Mesoproterozoic continental collision belt of Himalayan scale that contains various lines of evidence suggesting an early plateau\|type evolution. Here we discuss this evidence and draw comparisons with the prime example of a present day plateau in a continental collision setting, the Tibetan plateau.展开更多
This paper deals with the chemical and isotopic compositions of escaped gases from the Rehai geothermal area in Tengchong county of Yunnan Province. Results indicate that there is the mantle-derived magmatic intrusion...This paper deals with the chemical and isotopic compositions of escaped gases from the Rehai geothermal area in Tengchong county of Yunnan Province. Results indicate that there is the mantle-derived magmatic intrusion in shallow crust at this area. Modern mantle-derived mag-matic volatiles are being released currently in a steady stream by way of active faults. The escaped gases are mostly composed of CO2, together with subordinate amounts of H2S, N2, H2, CH4, SO2, CO and He. At the studied area, the north-south directed fault is the deepest, and it may be interlinked with the deep-seated thermal reservoir that would be directly recharged by the mantle-derived magmatic volatile. The He, C isotopic evidence reveals that the modern active magma beneath Rehai area may originate from the historical mantle-derived magma which caused the latest eruptive activity of volcanoes in that region.展开更多
A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb ...A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.展开更多
文摘The development of a plateau is an integral part of the evolution of recent large orogens. This is suggested by the presence of wide regions of high topographic relief in many Phanerozoic collisional belts, with the Tibetan, Anatolian, Altiplano and Colorado plateaus forming the most often cited examples. To date, plateaus have not been documented in Proterozoic orogens. However, if large Proterozoic convergent belts developed plateaus, evidence should be preserved in the geologic record.Proterozoic belts expose deeper crustal levels that are not directly accessible in modern analogues. Therefore, if they represent the final product of a plateau style evolution, their study may give direct insight on the nature of the middle to lower crust beneath modern orogenic plateaus. The Grenville Province of the Canadian Shield is a Mesoproterozoic continental collision belt of Himalayan scale that contains various lines of evidence suggesting an early plateau\|type evolution. Here we discuss this evidence and draw comparisons with the prime example of a present day plateau in a continental collision setting, the Tibetan plateau.
文摘This paper deals with the chemical and isotopic compositions of escaped gases from the Rehai geothermal area in Tengchong county of Yunnan Province. Results indicate that there is the mantle-derived magmatic intrusion in shallow crust at this area. Modern mantle-derived mag-matic volatiles are being released currently in a steady stream by way of active faults. The escaped gases are mostly composed of CO2, together with subordinate amounts of H2S, N2, H2, CH4, SO2, CO and He. At the studied area, the north-south directed fault is the deepest, and it may be interlinked with the deep-seated thermal reservoir that would be directly recharged by the mantle-derived magmatic volatile. The He, C isotopic evidence reveals that the modern active magma beneath Rehai area may originate from the historical mantle-derived magma which caused the latest eruptive activity of volcanoes in that region.
基金supported by the Ministry of Land and Resources of China under grant No.201211095
文摘A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.
