Dunite Xenoliths and Olivine Xenocrysts in Gabbro from Taihang Mountains: Characteristics of Mesozoic Lithospheric Mantle in Central China  

作　　者：许文良 王春光 杨德彬 王枫 裴福萍 

机构地区：[1]College of Earth Sciences, Jilin University [2]State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences

出　　处：《Journal of Earth Science》2010年第5期692-710,共19页地球科学学刊（英文版）

基　　金：supported by the National Natural Science Foundation of China (No. 90814003);the Ministry of Science and Technology of China (No. 2009CB825005);the Ministry of Education of China (No. 200801830039);the MOST Special Fund from the State Key Laboratory of Geo-logical Processes and Mineral Resources, China University of Geosciences

摘　　要：This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi＇anli （西安里） hornblende （Hb）-gahbros from the southern Taihang （太行） Mountains, with the aim of constraining the nature of the Mesozoic lithospheric mantle in Central China. Rounded dunite xenoliths are 1-3 cm3 in size and display porphyroelastic, tabular, and protogranular textures. Chromite with Cr#=60-89 is common in the xenoliths. Oilvine xenocrysts of 4-6 mm in size are also found in the Hb-gabbros. Orthopyroxene reaction rims are commonly observed around olivine xenocrysts or between dunite xenoliths and host rocks. The porphyroclastic olivines within dunite xenoliths and olivine xenoerysts have kink bands and Mg#=83-94. The Mg# of olivine cores and rims are 89-94 （average, 90） and 83-86 （average, 84.4）, respectively. The CaO contents of all olivines from the xenoliths and xenocrysts are less than 0.1 wt.%, suggesting a Hthospheric mantle origin. The Ca content （214 ppm-818 ppm） and Ti content （15 ppm-137 ppm） in the xenoliths and xenocrysts are similar to those of olivines from the dunite xenoliths, but are much higher than those of olivines from harzburgite and lherzolite xenoliths in the Fushan （符山） intrusion. This finding implies that the xenoliths and xenocrysts may have originated from harzburgites or lherzolites that were intensively modified by silica-rich melts. This result, combined with high Mg# （92-94） of olivine cores from the dunite xenoliths and xenocrysts, indicates that these ofivine xenocrysts and dunite xenoliths could represent the residue of ancient （Archean or Paleopro. terozoic） lithospheric mantle and might have experienced the same intensive modification by silica-rich melts as the host magma, resulting in enrichment in MgO and SiO2.This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi＇anli （西安里） hornblende （Hb）-gahbros from the southern Taihang （太行） Mountains, with the aim of constraining the nature of the Mesozoic lithospheric mantle in Central China. Rounded dunite xenoliths are 1-3 cm3 in size and display porphyroelastic, tabular, and protogranular textures. Chromite with Cr#=60-89 is common in the xenoliths. Oilvine xenocrysts of 4-6 mm in size are also found in the Hb-gabbros. Orthopyroxene reaction rims are commonly observed around olivine xenocrysts or between dunite xenoliths and host rocks. The porphyroclastic olivines within dunite xenoliths and olivine xenoerysts have kink bands and Mg#=83-94. The Mg# of olivine cores and rims are 89-94 （average, 90） and 83-86 （average, 84.4）, respectively. The CaO contents of all olivines from the xenoliths and xenocrysts are less than 0.1 wt.%, suggesting a Hthospheric mantle origin. The Ca content （214 ppm-818 ppm） and Ti content （15 ppm-137 ppm） in the xenoliths and xenocrysts are similar to those of olivines from the dunite xenoliths, but are much higher than those of olivines from harzburgite and lherzolite xenoliths in the Fushan （符山） intrusion. This finding implies that the xenoliths and xenocrysts may have originated from harzburgites or lherzolites that were intensively modified by silica-rich melts. This result, combined with high Mg# （92-94） of olivine cores from the dunite xenoliths and xenocrysts, indicates that these ofivine xenocrysts and dunite xenoliths could represent the residue of ancient （Archean or Paleopro. terozoic） lithospheric mantle and might have experienced the same intensive modification by silica-rich melts as the host magma, resulting in enrichment in MgO and SiO2.

关 键 词：North China craton Xi＇anli Hb-gabbro DUNITE XENOCRYST lithospheric mantle. 

分 类 号：P588.125[天文地球—岩石学]