The present study is the first report of a Miocene mafic dyke from the Dahuichang, in the Western Hills of Beijing. The dyke cuts the fossil-dated Changxindian Formation of Eocene sequences and yields K-Ar ages of 14-...The present study is the first report of a Miocene mafic dyke from the Dahuichang, in the Western Hills of Beijing. The dyke cuts the fossil-dated Changxindian Formation of Eocene sequences and yields K-Ar ages of 14-15 Ma. The dyke is fine-grained diabase and has 49.84%-50.81% SiO2 and 3.56-3.97% Na2O＋K2O, high TiO2 （1.65%-1.93%） and MgO （7.36%-9.85%）, and low K2O （〈1.22%） contents, with Na2O〉K2O and slightly varied magnesium numbers （Mg#=55.54-62.74）. In trace elements geochemistry, the dyke is very similar to the Miocene basalts from Jining and Hanuoba. The enrichment of light rare earth elements （[La/Yb]N=5.03-6.12） and large ion lithophile elements （LILEs）, no negative Eu anomalies, relatively high Cr （265-326 ppm） and Ni （155-262 ppm）, and almost constant V concentrations （194-213 ppm） reveal that the composition close to the primary basaltic magma from an enriched-mantle source, with little crustal contamination and fractional crystallization. The basaltic magma was possibly derived from the upwelling asthenosphere mantle beneath eastern China during the Miocene lithospheric thinning.展开更多
Mesozoic regional metamorphism took plaee in Western Hills of Beijing, China, in which platformal and diwa struetural layers were involved. In Zhoukoudian, south of Western Hills, there was low-amphibolite facies in t...Mesozoic regional metamorphism took plaee in Western Hills of Beijing, China, in which platformal and diwa struetural layers were involved. In Zhoukoudian, south of Western Hills, there was low-amphibolite facies in the Triassie as staurolite and kyanite zones were confined to decollements: with decroue in the temperature and pressure in the Jurassic,greenschist facies appeared when chloritoid and andaulusite rones were formed extensively.Intraformational folds and bedding-parallel ductile shear zones are common in Zhoukoudian where regional metamorphism is relatively strong. These phenomena are seldom seen in diwatype orogens and deserve further tesearch in the future.展开更多
Multiple methods were applied to study the deformation characteristics of hornblende in Archean plagioamphibolite mylonite from the Western Hills(Beijing),including optical microscopy(OM),electron backscatter diffract...Multiple methods were applied to study the deformation characteristics of hornblende in Archean plagioamphibolite mylonite from the Western Hills(Beijing),including optical microscopy(OM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),and electron probe microanalysis(EPMA).The hornblendes are σ and δ type porphyroclasts with the new-born needle shaped grains as their tails.The analysis of lattice preferred orientation(LPO) of both the porphyroclasts and the new-born grains shows that the main slip system of the deformed hornblende is(100)<001>,suggesting that the fabric characteristics of new-born grains inherit that of porphyroclasts.Sub-microstructures show the porphyroclast core is dominated by dislocation tangle,little or no dislocations in the new-born grains,and the subgrains confined by dislocations in the transition zone between porphyroclasts and new-born grains.By using plagioclase-hornblende geothermometry and hornblende geobarometry,the estimated temperature and pressure of porphyroclasts are 675.3-702.9℃ and 0.29-0.41 GPa and those of new-born grains are 614.1-679.0℃ and 0.11-0.31 GPa.The bulging recrystallization is summarized as deformation mechanisms of hornblende by the discussions of the microstructures,EBSD fabric,sub-microstructures,and the deformed temperature and pressure.展开更多
Sand glass deposits was located in the mid of the Western Desert of Iraq. It is situated within Rutba Formation (Ceno-manian). Ancient traditional mining method is still used in exploitation the unconsolidated white g...Sand glass deposits was located in the mid of the Western Desert of Iraq. It is situated within Rutba Formation (Ceno-manian). Ancient traditional mining method is still used in exploitation the unconsolidated white glass sand from glass sand quarry. The overburden thickness ranges from 2 to 4 m in average. Termite hills were observed around the glass sand quarry extending far from the quarry area. Termites could burrows down and penetrate the sand glass bringing it up to the surface. The depth of penetration reaches more than 35 m. The field observation of the white color of termite hills which are built up by sand glass gave a good indicator for the hidden subsurface deposit and it appears to be a surface signature for finding glass sand directly under the termite hills. The scattered white hills of glass sand on the surface with high content of SiO2, concordant Zr/Hf and Th/U ratios and heavy mineral distribution in both of quarry and termite hills provide a strong evidence of that those termite hills could be an effective tool for exploring subsurface hidden glass sand up to 35 m depth.展开更多
基金funded by the National NaturalScience Foundation of China(40672130)the Instrumental Analysis Fund of Peking University
文摘The present study is the first report of a Miocene mafic dyke from the Dahuichang, in the Western Hills of Beijing. The dyke cuts the fossil-dated Changxindian Formation of Eocene sequences and yields K-Ar ages of 14-15 Ma. The dyke is fine-grained diabase and has 49.84%-50.81% SiO2 and 3.56-3.97% Na2O＋K2O, high TiO2 （1.65%-1.93%） and MgO （7.36%-9.85%）, and low K2O （〈1.22%） contents, with Na2O〉K2O and slightly varied magnesium numbers （Mg#=55.54-62.74）. In trace elements geochemistry, the dyke is very similar to the Miocene basalts from Jining and Hanuoba. The enrichment of light rare earth elements （[La/Yb]N=5.03-6.12） and large ion lithophile elements （LILEs）, no negative Eu anomalies, relatively high Cr （265-326 ppm） and Ni （155-262 ppm）, and almost constant V concentrations （194-213 ppm） reveal that the composition close to the primary basaltic magma from an enriched-mantle source, with little crustal contamination and fractional crystallization. The basaltic magma was possibly derived from the upwelling asthenosphere mantle beneath eastern China during the Miocene lithospheric thinning.
文摘Mesozoic regional metamorphism took plaee in Western Hills of Beijing, China, in which platformal and diwa struetural layers were involved. In Zhoukoudian, south of Western Hills, there was low-amphibolite facies in the Triassie as staurolite and kyanite zones were confined to decollements: with decroue in the temperature and pressure in the Jurassic,greenschist facies appeared when chloritoid and andaulusite rones were formed extensively.Intraformational folds and bedding-parallel ductile shear zones are common in Zhoukoudian where regional metamorphism is relatively strong. These phenomena are seldom seen in diwatype orogens and deserve further tesearch in the future.
基金supported by the National Natural Science Foundation of China (Grant No.40772133)
文摘Multiple methods were applied to study the deformation characteristics of hornblende in Archean plagioamphibolite mylonite from the Western Hills(Beijing),including optical microscopy(OM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),and electron probe microanalysis(EPMA).The hornblendes are σ and δ type porphyroclasts with the new-born needle shaped grains as their tails.The analysis of lattice preferred orientation(LPO) of both the porphyroclasts and the new-born grains shows that the main slip system of the deformed hornblende is(100)<001>,suggesting that the fabric characteristics of new-born grains inherit that of porphyroclasts.Sub-microstructures show the porphyroclast core is dominated by dislocation tangle,little or no dislocations in the new-born grains,and the subgrains confined by dislocations in the transition zone between porphyroclasts and new-born grains.By using plagioclase-hornblende geothermometry and hornblende geobarometry,the estimated temperature and pressure of porphyroclasts are 675.3-702.9℃ and 0.29-0.41 GPa and those of new-born grains are 614.1-679.0℃ and 0.11-0.31 GPa.The bulging recrystallization is summarized as deformation mechanisms of hornblende by the discussions of the microstructures,EBSD fabric,sub-microstructures,and the deformed temperature and pressure.
文摘Sand glass deposits was located in the mid of the Western Desert of Iraq. It is situated within Rutba Formation (Ceno-manian). Ancient traditional mining method is still used in exploitation the unconsolidated white glass sand from glass sand quarry. The overburden thickness ranges from 2 to 4 m in average. Termite hills were observed around the glass sand quarry extending far from the quarry area. Termites could burrows down and penetrate the sand glass bringing it up to the surface. The depth of penetration reaches more than 35 m. The field observation of the white color of termite hills which are built up by sand glass gave a good indicator for the hidden subsurface deposit and it appears to be a surface signature for finding glass sand directly under the termite hills. The scattered white hills of glass sand on the surface with high content of SiO2, concordant Zr/Hf and Th/U ratios and heavy mineral distribution in both of quarry and termite hills provide a strong evidence of that those termite hills could be an effective tool for exploring subsurface hidden glass sand up to 35 m depth.
