Textural and chemical zoning in garnets related to mantle metasomatism and deformation processes
摘要:
A few texturally-zoned garnets were found in a polymict peridotite (JJG1414) from the Cretaceous kimberlite, Kimberley, South Africa. The systematic analyses of electron and ion microprobe as well as laser fluorination technique reveal the existencal of marked elemental and oxygen isotopic zonation in these garnets, corresponding to the textural zonation. The rims are normally enriched in Ca, Ti, Cr, LREE, Sr, Nb, and depleted in Mg, Al and O-18. It is demonstrated that these garnets were infiltrated by melts/fluids, probably representing the disequilibrated products of fluid-assisted mantle deformation.
K-Ar age of the Cenozoic volcanic rocks in the Nangqen Basin, Qinghai Province and its geological significance
作者:Wanming Deng、Hongjuan Sun、Yuquan Zhang
DOI:10.1007/bf02884983
日期:2000.6
The Nangqen Basin is one of the typical shearing-extensional basins situated in the north part of the Hengduan Mts. Nine ages of the Cenozoic volcanic rocks from the basin by K-Ar isotope-dilution technique have been reported in the note. The apparent ages of whole rock and separated biotite range from 32.04 to 36.50 Ma. The Ar-40-K (%) correlation isochronal line shows that there existed neither argon excessing, or radiogenetic argon loosing, i.e. the age represents the true diagenetic time. Volcanic activity in this area occurred in the post-collision environment and is controlled by lithosphere substantial thickening and violent intercontinental shearing-strike slip faults. There is age difference of the magmatic activity in the east, the west and the north Tibet. The multi-periodic eruption-intrusion of the magmatic melt since Cenozoic is a tracer showing the pulsating uplift of the Tibetan Plateau.