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...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 gamed. corresponding to the textural zonation. The rims are normally enriched in Ca, Ti, Cr, LREE. Sr, Nb, and depleted in Mg, Al and 18O. It is demonstrated that these gamats were infiltrated by melts/fiuids, probably representing the disequilibrated products of fluid-asssted mantle deformation.展开更多
Diffusion modeling of zoning profiles in eclogite garnets from three different tectonic units of Mt. Dabie, UHPM unit, HPM unit and northern Dabie, was used to estimate the relative time span and cooling rates of thes...Diffusion modeling of zoning profiles in eclogite garnets from three different tectonic units of Mt. Dabie, UHPM unit, HPM unit and northern Dabie, was used to estimate the relative time span and cooling rates of these rocks. Modeling result for the Huangzhen eclogite garnet shows that the maximal time span for the diffusion-adjustment process is about 22 Ma since the peak-temperature metamorphism, which is the maximum time span from amphibolite facies metamorphism to greenschist facies metamorphism. The Bixiling eclogites had subjected to a cooling process at a rate of ～10℃/Ma from 750℃ to 560℃ during 20 Ma. The second cooling stage of the Raobazhai eclogite following granulite-facies metamorphism is an initial fast cooling process at a rate of about 25℃/Ma and then slowed down gradually. All these belong to a coherent Dabie collision orogen with differences in subduction depth and exhumation/uplifting path.展开更多
Danba （丹巴） domal metamorphic terrain belongs to Songpan （松潘）-Ganze （甘孜） orogenic belt, where typical Barrovian and Buchan metamorphic zones are preserved. The former included chlorite, biotite, garnet, sta...Danba （丹巴） domal metamorphic terrain belongs to Songpan （松潘）-Ganze （甘孜） orogenic belt, where typical Barrovian and Buchan metamorphic zones are preserved. The former included chlorite, biotite, garnet, staurolite, kyanite and sillimanite zones, while the latter only developed silimanite＋muscovite and sillimanite＋K-feldspar zones. Integrated study has been carried on metamorphic reactions of garnet production and consumption, P-T paths and P-T-X-M phase relation and thermal tectonic model for Danba metamorphic zones. Petrological textures in thin sections show that garnet production and consumption in kyanite-sillimanite zone is mainly attributed to ChI＋Ms＋PI＋Q= Grt＋Bt＋H20 and kyanite=sillimanite respectively. Based on mineral compositions, the geothermo- barometry gives an average P, T condition of （4.9±0.3）×10^8 Pa, 543±30 ℃ for the first growth stage of the garnet and （5.8±0.3）×10^8 Pa, 534±29 ℃ for the second stage of garnet growth respectively. Anti-counter clockwise P-T paths were drawn using Gibbs method by NCMnKFMASH system for sample G98686 in the kyanite zone. The P-T-X-M modeling for the first mineral assemblages shows that the prediction is similar to the measured values in gossular, almandine and spessartine but mole fraction of pyrope and Fe/（Fe＋Mg） deviated far from the contours; while that for the second mineral assemblages exhibits that the prediction is consistent with the measured value of pyrope, grossular content and Fe/（Fe＋Mg） of garnet. A thermal tectonic model that there are at least three structure levels across the thrust-decollement zones is presented according to the P-T paths, metamorphic grades and deformation styles for the staurolite-kyanite zone of the Barrovian type metamorphism, which will provide some constraints for the evolution of the nappe complex.展开更多
This paper is supported by the Special Doctoral Grant of the Ministry of Education of China （No. 98049114） and the National Natural Science Foundation of China （No. 49972023）.
文摘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 gamed. corresponding to the textural zonation. The rims are normally enriched in Ca, Ti, Cr, LREE. Sr, Nb, and depleted in Mg, Al and 18O. It is demonstrated that these gamats were infiltrated by melts/fiuids, probably representing the disequilibrated products of fluid-asssted mantle deformation.
文摘Diffusion modeling of zoning profiles in eclogite garnets from three different tectonic units of Mt. Dabie, UHPM unit, HPM unit and northern Dabie, was used to estimate the relative time span and cooling rates of these rocks. Modeling result for the Huangzhen eclogite garnet shows that the maximal time span for the diffusion-adjustment process is about 22 Ma since the peak-temperature metamorphism, which is the maximum time span from amphibolite facies metamorphism to greenschist facies metamorphism. The Bixiling eclogites had subjected to a cooling process at a rate of ～10℃/Ma from 750℃ to 560℃ during 20 Ma. The second cooling stage of the Raobazhai eclogite following granulite-facies metamorphism is an initial fast cooling process at a rate of about 25℃/Ma and then slowed down gradually. All these belong to a coherent Dabie collision orogen with differences in subduction depth and exhumation/uplifting path.
基金supported by the National Natural Science Foundation of China (Nos. 40472097, 90814006)Re-search Fund for the Doctoral Program of Higher Education of China (No. 20070491516)
文摘Danba （丹巴） domal metamorphic terrain belongs to Songpan （松潘）-Ganze （甘孜） orogenic belt, where typical Barrovian and Buchan metamorphic zones are preserved. The former included chlorite, biotite, garnet, staurolite, kyanite and sillimanite zones, while the latter only developed silimanite＋muscovite and sillimanite＋K-feldspar zones. Integrated study has been carried on metamorphic reactions of garnet production and consumption, P-T paths and P-T-X-M phase relation and thermal tectonic model for Danba metamorphic zones. Petrological textures in thin sections show that garnet production and consumption in kyanite-sillimanite zone is mainly attributed to ChI＋Ms＋PI＋Q= Grt＋Bt＋H20 and kyanite=sillimanite respectively. Based on mineral compositions, the geothermo- barometry gives an average P, T condition of （4.9±0.3）×10^8 Pa, 543±30 ℃ for the first growth stage of the garnet and （5.8±0.3）×10^8 Pa, 534±29 ℃ for the second stage of garnet growth respectively. Anti-counter clockwise P-T paths were drawn using Gibbs method by NCMnKFMASH system for sample G98686 in the kyanite zone. The P-T-X-M modeling for the first mineral assemblages shows that the prediction is similar to the measured values in gossular, almandine and spessartine but mole fraction of pyrope and Fe/（Fe＋Mg） deviated far from the contours; while that for the second mineral assemblages exhibits that the prediction is consistent with the measured value of pyrope, grossular content and Fe/（Fe＋Mg） of garnet. A thermal tectonic model that there are at least three structure levels across the thrust-decollement zones is presented according to the P-T paths, metamorphic grades and deformation styles for the staurolite-kyanite zone of the Barrovian type metamorphism, which will provide some constraints for the evolution of the nappe complex.
基金This paper is supported by the Special Doctoral Grant of the Ministry ofEducation of China(No.98049114)and the National Natural Science Foundation of China(No.49972023).
文摘This paper is supported by the Special Doctoral Grant of the Ministry of Education of China （No. 98049114） and the National Natural Science Foundation of China （No. 49972023）.
