In 1952,China established its first sand control research institute in Zhangwu County.Located on the southeast edge of the Horqin Sandy Land,90%of Zhangwu was covered by sandy terrain at that time.Qu Liping,a forest p...In 1952,China established its first sand control research institute in Zhangwu County.Located on the southeast edge of the Horqin Sandy Land,90%of Zhangwu was covered by sandy terrain at that time.Qu Liping,a forest planting worker in Zhangwu,recalled,“Sometimes in the morning,people couldn't even push open their doors because they would be half buried in sand.”展开更多
Ten volcanic samples at Zhangwu,western Liaoning Province,North China were selected for a sys-tematic geochemical,mineralogical and geochronological study,which provides an opportunity to ex-plore the interaction betw...Ten volcanic samples at Zhangwu,western Liaoning Province,North China were selected for a sys-tematic geochemical,mineralogical and geochronological study,which provides an opportunity to ex-plore the interaction between the continental crust and mantle beneath the north margin of the North China craton.Except one basalt sample(SiO2=50.23%),the other nine samples are andesitic with SiO2 contents ranging from 53%to 59%.They have relatively high MgO(3.4%―6.1%,Mg#=50―64)and Ni and Cr contents(Ni 27×10?6―197×10?6,Cr 51×10?6―478×10?6).Other geochemical characteristics of Zhangwu high-Mg andesites(HMAs)include strong fractionation of light rare earth elements(LREE)from heavy rare earth elements(HREE),and Sr from Y,with La/Yb greater than 15,and high Sr/Y(34―115).Zircons of andesite YX270 yield three age groups with no Precambrian age,which precludes ori-gin of the Zhangwu HMAs from the partial melting of the Precambrian crust.The oldest age group peaking at 253 Ma is interpreted to represent the collision of the Siberia block and the North China block,resulting in formation of the Central Asian orogenic belt by closure of the Mongol-Okhotsk Ocean.The intermediate age group corresponds to the basalt underplating which caused the wide-spread coeval granitoids in the North China craton with a peak 206Pb/238U age of 172 Ma.The youngest age group gives a 206Pb/238U age of 126±2 Ma,which is interpreted as the eruption age of the Zhangwu HMAs.The high 87Sr/86Sri(126 Ma)>0.706 and lowεNd(t)=?6.36―?13.99 of the Zhangwu HMAs are distinct from slab melts.The common presence of reversely zoned clinopyroxene phenocrysts in the Zhangwu HMAs argues against the origin of the Zhangwu HMAs either from melting of the water saturated mantle or melting of the lower crust.In light of the evidence mentioned above,the envisaged scenario for the formation of the Zhangwu HMAs is related to the basaltic underplating at the base of the crust,which led to the thickening of the lower crust and formation of lower crustal eclogite,followed by foundering of the eclogitic lower crust into the asthenosphere.The foundered eclogite then melted and the resul-tant melts interacted with surrounding peridotite during their upward transport,which finally produced the high-Mg andesites.This well explains the high-Mg adakitic characters and absence of ancient in-herited zircon in the Zhangwu lavas.展开更多
文摘In 1952,China established its first sand control research institute in Zhangwu County.Located on the southeast edge of the Horqin Sandy Land,90%of Zhangwu was covered by sandy terrain at that time.Qu Liping,a forest planting worker in Zhangwu,recalled,“Sometimes in the morning,people couldn't even push open their doors because they would be half buried in sand.”
基金Co-supported by the National Natural Science Foundation of China(40521001,40673019)Ministry of Education of China(B07039,IRT0441)the Key Labo-ratory of Orogenic Belts and Crustal Evolution
文摘Ten volcanic samples at Zhangwu,western Liaoning Province,North China were selected for a sys-tematic geochemical,mineralogical and geochronological study,which provides an opportunity to ex-plore the interaction between the continental crust and mantle beneath the north margin of the North China craton.Except one basalt sample(SiO2=50.23%),the other nine samples are andesitic with SiO2 contents ranging from 53%to 59%.They have relatively high MgO(3.4%―6.1%,Mg#=50―64)and Ni and Cr contents(Ni 27×10?6―197×10?6,Cr 51×10?6―478×10?6).Other geochemical characteristics of Zhangwu high-Mg andesites(HMAs)include strong fractionation of light rare earth elements(LREE)from heavy rare earth elements(HREE),and Sr from Y,with La/Yb greater than 15,and high Sr/Y(34―115).Zircons of andesite YX270 yield three age groups with no Precambrian age,which precludes ori-gin of the Zhangwu HMAs from the partial melting of the Precambrian crust.The oldest age group peaking at 253 Ma is interpreted to represent the collision of the Siberia block and the North China block,resulting in formation of the Central Asian orogenic belt by closure of the Mongol-Okhotsk Ocean.The intermediate age group corresponds to the basalt underplating which caused the wide-spread coeval granitoids in the North China craton with a peak 206Pb/238U age of 172 Ma.The youngest age group gives a 206Pb/238U age of 126±2 Ma,which is interpreted as the eruption age of the Zhangwu HMAs.The high 87Sr/86Sri(126 Ma)>0.706 and lowεNd(t)=?6.36―?13.99 of the Zhangwu HMAs are distinct from slab melts.The common presence of reversely zoned clinopyroxene phenocrysts in the Zhangwu HMAs argues against the origin of the Zhangwu HMAs either from melting of the water saturated mantle or melting of the lower crust.In light of the evidence mentioned above,the envisaged scenario for the formation of the Zhangwu HMAs is related to the basaltic underplating at the base of the crust,which led to the thickening of the lower crust and formation of lower crustal eclogite,followed by foundering of the eclogitic lower crust into the asthenosphere.The foundered eclogite then melted and the resul-tant melts interacted with surrounding peridotite during their upward transport,which finally produced the high-Mg andesites.This well explains the high-Mg adakitic characters and absence of ancient in-herited zircon in the Zhangwu lavas.
文摘松辽盆地南部彰武断陷九佛堂组发育大套半深湖—深湖相暗色泥页岩夹油页岩层.在岩心观察、薄片鉴定和扫描电镜分析基础上,结合泥页岩的分布、电性和地化特征、含油气性、储集和保存条件等,研究九佛堂组富有机质的暗色泥页岩的页岩油气资源潜力.结果表明：九佛堂组暗色泥页岩在测井曲线上具有＂三高一低＂的响应特征,纵向上厚度大,可识别上、下两段泥页岩层系,横向上展布较广;有机质丰度高,达到好的烃源岩标准,干酪根以Ⅰ型和Ⅱ1型为主,镜质体反射率（Ro）为0.54%~1.10%;泥页岩含油气性较好,晶间、粒间微孔隙和微裂缝较发育;脆性矿物平均质量分数高达51.4%,易于储层压裂改造.九佛堂组沉积后期构造活动较弱,有利于页岩油气的保存.运用概率体积法估算页岩油资源量为12 442.0×104 t.
