Relationship between Crustal 3D Density Structure and the Earthquakes in the Longmenshan Range and Adjacent Areas

This paper presents the 3D density structure of crust in the Longmenshan range and adjacent areas,with constraints from seismic and density data.The density structure of crust shows that the immense boundary plane of density distribution in relation to the Longmeshan fault belt is extended downward to～80 km deep.This density boundary plane dips towards the northwest and crosses the Moho.With the proximity to the Longmenshan fault belt,it has a larger magnitude of undulation in the upper and middle crust ...     

甘肃西秦岭两类新生代钾质火山岩:岩石地球化学与成因

甘肃西秦岭地区存在钾霞橄黄长岩和钾质粗面玄武岩(钾玄岩)两类钾质火山岩,出露在甘肃西秦岭礼县、宕昌县等,地理坐标大致相当于104°20′～104°50′E,33°30′～34°10′N。钾霞橄黄长岩是一种不含斜长石,但普遍含有高钛金云母、黄长石、白榴石、霞石的岩石,全岩化学成分具低SiO2和Al2O3,富TiO2、CaO、MgO和高K/Na、高Mg#值的特征;钾质粗面玄武岩(钾玄岩)含有大量斜长石但是缺乏高钛金云母、黄长石、白榴石和霞石,全岩化学中SiO2、Al2O3明显高于前者,而TiO2、CaO、MgO、K/Na和Mg#值要比钾霞橄黄长岩低。钾霞橄黄长岩的全岩K/Ar和金云母单矿物的39Ar/40Ar同位素定年落在7.1～23Ma,而钾玄岩的全岩39Ar/40Ar同位素定年落在9Ma左右,因此它们同为中新世产物。两类钾质火山岩具有相似的富集不相容元素和轻稀土的特征。两类钾质火山岩的初始87Sr/86Sr分别在0.70403～0.70749和0.70412～0.70522;143Nd/144Nd分别在0.51274～0.51294和0.51265～0.51276;εNd分别在1.12～5.95和0.3～2.3。206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别落到18.3746～18.9986、15.529～15.6693和38.4971～39.4144。在火山岩源区示踪的143Nd/144Nd-87Sr/86Sr,207Pb/204Pb-206Pb/204Pb,208Pb/204Pb-206Pb/204Pb,143Nd/144Nd-206Pb/204Pb,87Sr/86Sr-206Pb/204Pb和Ba/Nb-La/Nb图解中,一致显示两类钾质火山岩具有与OIB相似的地球化学特征,源区可能与地幔柱有关,并具有EM1、DMM和HIMU端员混合特征。结合前人对该区深部地球物理和断裂构造的研究,论证了火山岩的起源与成因,指出作为对印度—欧亚大陆强烈碰撞的吸收与调节,高原下软流圈地幔流沿400km界面向北东方向的侧向流动以及西秦岭周边克拉通块体的阻挡,是形成西秦岭断裂系左行走滑特征和巨大拉分盆地的主要原因,也是导致西秦岭新生代两类钾质火山岩和碳酸岩起源与成因的动力学机制,较好地解释了西秦岭新生代岩浆作用起源深度大,具有地幔柱源的地球化学特征,岩石组合与地球化学有别于高原内部及其周边地区新生代钾质火山岩的原因。     

Tourmaline as metallogenic indicator: Examples from paleo-proterozoic Pb-Zn and Cu-Au deposits of Rajasthan

Petrology and mineral chemistry of ten types of tourmalines from Pb-Zn bearing strata-bound exhalative deposits and Cu-Au-Fe deposits, presumably of IOCG-type, from Rajasthan are presented. The Pb-Zn deposits studied include Agucha, Kayar and Dariba areas in central Rajasthan, each of which is widely separated in space and occurs in isolated but coeval basins within the Archaean basement. The Cu-Au deposits include Ghagri, Bada Talav, Dugocha and Bhukia areas in southeast Rajasthan. The syngenetic Pb-Zn type and the epigenetic Cu-Au-Fe type of deposits are formed during the initial phase of Paleoproterozoic Aravalli Basin evolution with dominant deposition of shelf facies pelite-carbonate sequence of Debari Group. The post-depositional tectono-metamorphic history of the host rocks of Pb-Zn type and Cu-Au type deposits differ significantly with the former deposits showing higher metamorphic impress (amphibolite to lower granulite facies) than the latter (green schist facies).     

安徽宁国胡乐地区奥陶系层序地层学初探

宁国市胡乐镇鸿门—将军岭段新开公路旁奥陶系宁国组出露完好,通过对该段地层进行连续观察和分析研究,发现存在Ⅱ型不整合面、海侵面、最大海泛面等重要的地层界面,以及鲍玛序列、复理石建造等典型的沉积特征。根据海平面变化、地壳沉降和沉积物补给关系,采用基本层序调查方法,将该区奥陶纪地层层序划分为A、B、C、D、E5个层序。其中只有2个(C、E)为完整层序,其余3个(A、B、D)为不完整层序。研究表明,该地区奥陶系为深水盆地沉积,纵向岩性变化小,多数缺失低水位沉积,反映当时海平面升降变化幅度较小,但节奏性的韵律变化仍较明显。     

Variation in Solvent-Extractable Lipids and n-Alkane Compound-Specific Carbon Isotopic Compositions with Depth in a Southern China Karst Area Soil

Because literatures about the lipid compositions of modern soils in karst areas are scarce,we have studied the soil horizons overlying the Heshang(和尚) Cave that has provided paleoclimate records from speleothem lipid contents.Our analysis reveals a series of n-alkanes,free fatty acids,n-alkanols and n-alkan-2-ones distribution and relative abundance changing with the depth,and in which the ratios of the lower molecular weight to higher molecular weight n-alkanes,free fatty acids,n-alkanols and n-alkan-2-one...     

江西省泥盆纪岩石地层划分与对比

江西省泥盆纪地层发育,分布广泛,以非海相地层为主,赣西、赣南间夹海相地层。因区内不同地段的地层发育程度及沉积特征有明显差异,故可进一步划分出若干地层小区,各地层小区的岩石地层单位特征及划分各不相同,并根据植物、腕足类和鱼化石对江西省泥盆纪生物地层进行了探讨。     

皖中张八岭地区构造地层序列的建立与主要特征

通过对张八岭地区10幅1/5万地质填图资料分析与对关键地区的构造解剖,采用了构造地层学思路与方法,重新厘定了全区由多期变形所形成的构造型式及其制约的构造地层序列。在此基础上对西冷组的层序进行了重新划分,厘定了与周岗组的接触界面性质,讨论了原北将军组的构造属性及可能的时代归属。     

安徽贵池地区二叠系孤峰组露头层序地层

依据实测地层剖面的详细研究,将二叠系孤峰组分为四个三级层序,每个三级层序跨时平均约1.25Ma,其高频变化表现为:海侵体系域的粒序变化主要表现为下粗上细的正粒序组构特征,总体表现为自下而上沉积水体由浅变深的退积型旋回;高位体系域的粒序变化主要表现为下粗上细的正粒序组构特征,总体表现为自下而上沉积水体由深变浅的进积型旋回。     

湘南中生代火山岩中尖晶石二辉橄榄岩包体 Sm-Nd等时线年龄及地质意义

湖南宁远太阳山中生代玄武质火山岩内,产较丰富的尖晶石二辉橄榄岩包体。包体经人工碎样,镜下挑选了含铬尖晶石、镁橄榄石、含铬透辉石、斜方辉石、全岩5个样品,由国土资源部天津地质矿产研究所同位素室测试,得出 Sm-Nd全岩-单矿物等时线同位素年龄2702±19 Ma。进而根据测试结果和以往资料综合分析,认为华南陆块岩石圈是沿垂向演化增生的,由下往上依次为:上地幔岩垫托、结晶基底、褶皱基底、褶皱盖层、沉积盖层5个构造层。其中,上地幔岩起着底板垫托作用,形成于新太古代,为该地区最古老岩石。