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81.
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大别山石马地区榴辉岩P-T-t轨迹及其构造意义 总被引:7,自引:0,他引:7
在大别山石马地区榴辉岩石榴石中包裹有与柯石英同期的绿辉石,据此,将这里的榴辉岩相变质作用划分为早期的柯石英榴辉岩阶段和晚期重结晶榴辉岩阶段。它们的P-T-t轨迹表明:产于片麻岩中的榴辉岩至少经历了两阶段的抬升过程:(1)在221Ma(印支期)时,由于陆壳俯冲所产生的大规模逆冲构造使其快速抬升;(2)在134Ma(燕山期)陆壳俯冲后的拉张抬升环境下,榴辉岩随山体一起缓慢上升。 相似文献
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李曙光 《中国地球化学学报》1992,11(4):314-328
A new approach to the investigation of the Sm/Nd evolution of the upper mantle directly from the data on lherzolite xenoliths is described in this paper.It is demonstrated that the model age TCHUR of an unmetasomatic iherzolite zenolith ca represent the mean depletion age of its mantle source, thus presenting a correlation trend between f^Sm/Nd and the mean depletion age of the upper mantle from the data on xenoliths.This correlation trend can also be derived from the data on river suspended loads as well as from granitoids.Based on the correlation trend mentioned above and mean depletion ages of the upper mantle at various geological times, an evolution curve for the mean f^Sm/Nd value of the upper mantle through geological time has been established.It is suggested that the upwilling of lower mantle material into the upper mantle and the recycling of continental crust material during the Archean were more active ,thus maintaining fairly constantf^Sm/Nd and εNd values during this time period. Similarly ,an evolution curve for the mean f^Sm/Nd value of the continental crust through geological time has also been established from the data of continental crust material.In the light of both evolution curves for the upper mantle and continental crust ,a growth curve for the continental crust has been worked out ,suggesting that :(1)about 30%(in volume )of the present crust was present as the continental crust at 3.8 Ga ago ;(2)the growth rate was much lower during the Archean ;and (3)the Proterozoic is another major period of time during which the continental crust wsa built up . 相似文献
85.
弓长岭富磁铁矿床成因的地球化学模型 总被引:4,自引:0,他引:4
Based upon geological and geochemical data on the genesis of Gongchangling rich magnetite deposit, it is suggested that the deposit is of multigenesis, and a three-stage geochemical model for the genesis of the deposit is proposed : (1) Depositional stage : the deposition of banded low-grade ores (magnetite-quartzite) was accompanied by high-grade magnetite (hematite)-siderite ores which are intercalated with magnetite-quartzites as lenses or stratoid shoots. (2) Metaamorphic stage: In response to metamorphism, siderite was decomposed into magnetite and graphite with decreasing fo2 and increasing PCO2. On the margin of magnetitc-siderite ores or within the thin intercalated layers where fO2, was high relative to PCO2 were formed graphite-free rich magnetite ores. (3) Hydrothermal stage: As a result of later hydrothermal process diffusive metasomatism between the shoots and host rocks anti silica leaching took place, thus giving rise to the rich magnetite ores of metasomatic type, and altered rocks. 相似文献
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浙西南北园八都群石榴斜长角闪岩的变质特征及年代 总被引:3,自引:0,他引:3
浙西南北园的石榴斜长角闪岩是一次高角闪岩相变质作用的产物,原岩为玄武质火成岩。可分为两个演化过程,其一是高角闪岩相变质作用,变质温度约650±20℃,压力0.9~1.1GPa,形成石榴子石+用闪石+斜长石十单斜辉石±金红石的矿物组合;其二是石榴斜长角闪岩的减压退变质,形成透辉石+更-中长石的筛孔状分解结构及榍石环绕金红石的反应边结构。石榴斜长角闪岩的矿物Sm-Nd等时年龄为1468±19Ma,代表高角闪岩相变质时代,Rb-Sr等时年龄为1083±49Ma,反映退变质时代,它们各自反映了华夏古陆中晚元古代时期两次重要构造事件。 相似文献
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苏鲁超高压变质带东海青龙山高压正片麻岩中白云母的^40Ar/^39Ar年代学研究 总被引:7,自引:1,他引:7
作为东海青龙山榴辉岩围岩的高压变质的正片麻岩,其白云母的常规^40Ar/^39Ar年龄和Rb—Sr、Sm—Nd年龄一致,激光微区Ar同位素分析表明,白云母的Ar同位素分布也是均匀的。由此得出的初步结论是:①高压变质的正片麻岩中的白云母中不含过剩Ar,这类矿物可以作为^40Ar/^39Ar同位素测年的对象;②青龙山榴辉岩中的白云母含大量过剩氩,而作为其围岩的超高压正片麻岩中的白云母却不含过剩氩,这一事实证明了榴辉岩中白云母的过剩氩不是来自围岩,而是榴辉岩自身继承的。 相似文献