The Gangdise rockk belt is the northmost an4 petrochemically the most complex one of the three east-west striking intermedlate-acid rock belt in south Xizang. Rh-Sr whole rock isochronous dating was conducted on sampl...The Gangdise rockk belt is the northmost an4 petrochemically the most complex one of the three east-west striking intermedlate-acid rock belt in south Xizang. Rh-Sr whole rock isochronous dating was conducted on samples of different rocks collected aerossing this belt from Quxur throwgh Lhasa to Yangbajan, Results show that these rocks are not contemporaneous and can be roughly assigned to four periods: Indosinian (240±30 my), Early Yenshanian (160--180my), Late Yenshanian (80--100 my), and Himalayanian (20-40 my). Their initial ratios of Sr isotopes are relatively low (0.7033--0.7054). The relationship between Rb, Sr and the major components such as SiO2, K2Oand FeO are also investigated. It seems that, the formation and development of the Gangdise belt can be obviously related with the subduction and collision of the Indian plate with the Eurasian plate. The material that formed this rock belt probably originated from the upper marital or the partial molten products from oceanic crust.展开更多
Based upon the present research stratus on Nan Ling granites and in the view of the defferenees in the opinions on the ages and periodic division of Nan Ling granites existing among some research units concerned, a pr...Based upon the present research stratus on Nan Ling granites and in the view of the defferenees in the opinions on the ages and periodic division of Nan Ling granites existing among some research units concerned, a proposal has been snbmitted in the paper, pointing out that it is quite necessary to launch a discussion in the deeper-going way on the problem involving the ages of Nan Ling granites and their periodic division in the journal “GEOCHIMICA”. The main topics expected to be discussed are as follows : (1) The existanec of Hereynian granites and the possibility of the formation of non-orogenic granites; (2) The divisional boundary between Yeushanian and Indonsinian granites and their distributional characteristics; (3) The periodic sub-division of Yenshanian granites and their relatiouship with mineralization ; (4) The division of the ,ages of granites older than the Caledonian period.展开更多
Widespread in Southern Xizang are intermediate-acidic rocks characterized by their regular distribution in space and time. In order to explore their formation ages and genesis, we have determined the Rb-Sr whole rock ...Widespread in Southern Xizang are intermediate-acidic rocks characterized by their regular distribution in space and time. In order to explore their formation ages and genesis, we have determined the Rb-Sr whole rock isochron ages on granodiorite from the Quxu pluton in Kangdese belt (18m.y., Sr^87/Sr^88 initial ratio = 0.7036), gneissose two-mica granite from the Kangmar pluton in Lhagoi Kangri belt (484.55 ± 6.34 m.y.,Sr^87/Sr^86 initial ratio = 0.7186 ± 0.0018) ; and tourmaline-muscovite granite from the Gabug pluton in Himalaya belt (42.95 ± 2.6 m.y., Sr^87/Sr^84 initial ratio=0.7478±0.00097). From the initial Sr^87/Sr^86 ratios it is shown that the granodiorites are most likely to be derived from the upper mantle; the gneissose two-mica granites may contain significant amounts of sialic material during emplacement; and the tourmalinemusco vite granites are typically of crustal origin.展开更多
Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inherita...Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.展开更多
This paper is a summation of the discussions held since 1976 under this topic.Zonation and the unbalance rules regarding temporal and spatial distribution of granites,the relationship between granite formation and cru...This paper is a summation of the discussions held since 1976 under this topic.Zonation and the unbalance rules regarding temporal and spatial distribution of granites,the relationship between granite formation and crust movement, the series of mineralization and the cyclic nature of granitic magmatism are dealt with followed by a preliminary time division of granites based on our study. Nanling granites are classified into three broad categories, i.e., the Precambrian, Paleozoic and Mcsozoic granites.On the basis of geological setting, stratigraphieal evidence, isotopic age, spatial distribution, petrology, trace elements and accessory minerals the following subdivisions are suggested for Nanling granites: Szupunian (1063--1400my), Hsuehfangian (570--900my), early Caledonian (400--570my), late Caledonian (360-400my), Hercynian(230--360 my), Indosiuian (195±5--230 my), early Yenshanian (140±5-195±5 my).and late Yenshanian (70-140±5 my).展开更多
文摘The Gangdise rockk belt is the northmost an4 petrochemically the most complex one of the three east-west striking intermedlate-acid rock belt in south Xizang. Rh-Sr whole rock isochronous dating was conducted on samples of different rocks collected aerossing this belt from Quxur throwgh Lhasa to Yangbajan, Results show that these rocks are not contemporaneous and can be roughly assigned to four periods: Indosinian (240±30 my), Early Yenshanian (160--180my), Late Yenshanian (80--100 my), and Himalayanian (20-40 my). Their initial ratios of Sr isotopes are relatively low (0.7033--0.7054). The relationship between Rb, Sr and the major components such as SiO2, K2Oand FeO are also investigated. It seems that, the formation and development of the Gangdise belt can be obviously related with the subduction and collision of the Indian plate with the Eurasian plate. The material that formed this rock belt probably originated from the upper marital or the partial molten products from oceanic crust.
文摘Based upon the present research stratus on Nan Ling granites and in the view of the defferenees in the opinions on the ages and periodic division of Nan Ling granites existing among some research units concerned, a proposal has been snbmitted in the paper, pointing out that it is quite necessary to launch a discussion in the deeper-going way on the problem involving the ages of Nan Ling granites and their periodic division in the journal “GEOCHIMICA”. The main topics expected to be discussed are as follows : (1) The existanec of Hereynian granites and the possibility of the formation of non-orogenic granites; (2) The divisional boundary between Yeushanian and Indonsinian granites and their distributional characteristics; (3) The periodic sub-division of Yenshanian granites and their relatiouship with mineralization ; (4) The division of the ,ages of granites older than the Caledonian period.
文摘Widespread in Southern Xizang are intermediate-acidic rocks characterized by their regular distribution in space and time. In order to explore their formation ages and genesis, we have determined the Rb-Sr whole rock isochron ages on granodiorite from the Quxu pluton in Kangdese belt (18m.y., Sr^87/Sr^88 initial ratio = 0.7036), gneissose two-mica granite from the Kangmar pluton in Lhagoi Kangri belt (484.55 ± 6.34 m.y.,Sr^87/Sr^86 initial ratio = 0.7186 ± 0.0018) ; and tourmaline-muscovite granite from the Gabug pluton in Himalaya belt (42.95 ± 2.6 m.y., Sr^87/Sr^84 initial ratio=0.7478±0.00097). From the initial Sr^87/Sr^86 ratios it is shown that the granodiorites are most likely to be derived from the upper mantle; the gneissose two-mica granites may contain significant amounts of sialic material during emplacement; and the tourmalinemusco vite granites are typically of crustal origin.
文摘Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.
文摘This paper is a summation of the discussions held since 1976 under this topic.Zonation and the unbalance rules regarding temporal and spatial distribution of granites,the relationship between granite formation and crust movement, the series of mineralization and the cyclic nature of granitic magmatism are dealt with followed by a preliminary time division of granites based on our study. Nanling granites are classified into three broad categories, i.e., the Precambrian, Paleozoic and Mcsozoic granites.On the basis of geological setting, stratigraphieal evidence, isotopic age, spatial distribution, petrology, trace elements and accessory minerals the following subdivisions are suggested for Nanling granites: Szupunian (1063--1400my), Hsuehfangian (570--900my), early Caledonian (400--570my), late Caledonian (360-400my), Hercynian(230--360 my), Indosiuian (195±5--230 my), early Yenshanian (140±5-195±5 my).and late Yenshanian (70-140±5 my).
