Drought reconstruction in the Qilian Mountains over the last two centuries and its implications for large-scale moisture patterns

We present a composite tree-ring chronology from two sites of Qilian Juniper(Sabina przewalskii)in the northwestern Qilian Mountains(QM),Northwestern China.Precipitation in June was found to be the main limiting factor for tree-growth.The tree rings are also significantly and positively correlated with June precipitation over large areas of the northern Tibetan Plateau(TP).The authors thus consider that the tree- ring based drought reconstruction from 1803–2006 is representative of a large area drought hist...     

Geochemistry of granulite‐facies granitic rocks from Battye Glacier,northern Prince Charles Mountains,East Antarctica

Proterozoic basement outcrops in the vicinity of Battye Glacier, northern Prince Charles Mountains, are dominated by granulites and gneisses derived from felsic (granitoid) intrusive igneous rocks, and by pegmatites. Felsic orthopyroxene granulites, garnet leucogneisses and garnet pegmatites have major and trace element compositions of highly felsic, but not strongly fractionated, granites. The garnet leucogneisses and garnet pegmatites have S‐type characteristics, whereas the felsic granulites are probably I‐type, although their high Zr+Nb+Y+Ce abundances suggest possible A‐type affinities. Intermediate orthopyroxene ± clinopyroxene granulites mostly resemble I‐type quartz diorites, except for a small subgroup of samples (characterised by low Na₂O and K₂O, and high MgO, Ni, Cr and HREE) of uncertain affinities and significance. Element ratios involving LILE (e.g. K/Rb, Rb/Ba, Rb/Sr, K/La, La/Th) closely match those typical of the inferred granitoid protoliths, suggesting that these rocks have experienced relatively little LILE depletion (except possibly for U) during regional metamorphism. It is therefore inferred that metamorphism was probably broadly isochemical. Because the felsic and intermediate granulites and garnet leucogneisses are Sr‐depleted, Y‐undepleted and mostly have negative Eu anomalies they are inferred to be the products of partial melting of felsic crustal sources leaving plagioclase‐bearing residua. Plagioclase fractionation during crystallisation could also account for these characteristics, but K/Rb, Rb/Ba and Rb/Sr ratios in these rocks are not consistent with strong fractionation of feldspar. Garnet pegmatites differ chemically from garnet leucogneisses mainly in their lower Fe, Ti, Nb, Zn, Zr, Th and REE abundances and positive Eu anomalies, related to lower garnet, ilmenite and zircon contents in the garnet pegmatites. A genetic link between these two rock types, probably involving fractionation of these minerals during partial melting or crystallisation, is inferred. Incompatible‐element abundances suggest that generation of the Battye Glacier granitic magmas from felsic crust might have occurred in a mature continental magmatic arc possibly well removed from an active subduction trench or, perhaps, in an intracontinental setting.     

东天山库姆塔格发现辉长岩中钼的超常富集

在新疆东天山库姆塔格新发现了辉长岩中钼元素的超常富集,超过了目前的工业品位。从野外产状看,与钼矿化直接相关的岩石均为辉长岩,共两类:一是规模较小但全岩矿化的辉长岩脉;二是规模较大但没有矿化的辉长岩体;矿化的辉长岩脉穿插于非矿化的辉长岩体之中。虽然辉长岩体矿区东侧有中酸性岩浆岩存在,但野外产状和现有的物化探工作尚未发现钼矿化与中酸性岩浆岩有直接关系。无论辉长岩的形成与钼的富集是否属于同一次地质作用的产物,这都可能是一种尚未被认识的、全新的钼矿床(矿化)类型,具有重要的理论意义。     

黑河上游祁连山区植物群落随海拔生境的变化特征

基于79个样地的野外调查数据,采用双向指示种分析(TWINSPAN)等方法,研究了黑河上游祁连山浅山区、阴坡、阳坡3种典型类型植物群落随海拔梯度的变化特征.结果表明:浅山区植被属于山地荒漠类型;阴坡植被沿海拔升高依次分异为山地荒漠、山地森林和高山灌丛,海拔2 500m和3 300m是它们的海拔分界线;阳坡植被在海拔3 200m截然分异为干旱类型和湿润类型.乔木物种多样性随海拔变化难于形成一定的格局;灌木物种丰富度随海拔升高呈现多峰分布格局,总体上高海拔低、低海拔高;草本植物物种多样性随海拔升高呈单峰变化.以上生态型的各优势种分别占据不同的海拔范围,祁连山主要乔木青海云杉分布在海拔2 500～3 500m的阴坡,其郁闭度随海拔升高而降低,在海拔3 300m以上海拔区域为零星分布.     

祁连山地区能量平衡特征的模拟分析研究

利用VIC大尺度分布式水文模型,对祁连山地区2007年1—12月的能量平衡特征进行模拟分析.结果表明:该地区的地表能量平衡中感热通量占有主导地位,而潜热较小.春季,日尺度上的冻融循环过程造成的土壤湿度的增加是潜热通量较大原因;秋季的潜热通量主要是夏季的降水引起的,祁连山地区土壤湿度对大气的反馈效应较干旱区所需的时间尺度长.     

准噶尔盆地南缘新生代地层时代研究

对准噶尔盆地南缘金沟河剖面进行了磁性地层学研究,建立了该剖面精细的磁极性年代框架,并探讨了准噶尔盆地南缘新生代地层的年代。金沟河剖面出露的新生代地层厚约4160m,由老到新依次为安集海河组、沙湾组、塔西河组、独山子组和西域组。通过系统热退磁和剩磁测量,1285块样品获得特征剩磁,并由此建立该剖面自出露的安集海河组底部至西域组中部厚约3250m地层的磁极性柱。根据该剖面极性柱的变化特征和剖面中发现的两处脊椎动物化石,与2004年标准磁极性柱进行了对比。结果表明,金沟河剖面研究段地层的年代约为28.0—4.0Ma,其中安集海河组、沙湾组、塔西河组和独山子组的年代分别约为28.0—23.3Ma、23.3—17.5Ma、17.5—13.2Ma和13.2—6.0Ma,根据沉积速率外推得到的西域组的年代约为6.0—1.1Ma。与前人划分的准噶尔盆地南缘新生代地层的年代相比较,金沟河剖面磁性地层学确定的安集海河组、沙湾组和塔西河组的年代与前人的划分基本相符,而独山子组和西域组的年代则明显偏老。     

成矿概率面金属量法在东天山铜镍矿预测中的应用

地球化学方法被普遍应用于矿产资源定量预测,但多数方法都只是基于地球化学数据本身而进行的,较少考虑除成矿物质来源之外的诸如构造、地层等地质环境的影响,结果使估算的资源量不能够很好符合客观实际。在充分研究地质因素的基础上,认为物质基础和富集强度是矿床形成的重要条件,并据此对传统面金属量法进行了修正,建立了成矿概率面金属量法。该法可在一定程度上屏蔽虚假资源量。笔者采用成矿概率面金属量法对东天山地区铜镍矿的铜资源量进行了定量评价,效果较好。预测结果表明,东天山地区该类型铜矿资源潜力较大。     

西秦岭天水地区新生代酸性火山岩地球化学特征及其构造意义

西秦岭天水地区分布有新生代陆相酸性火山岩，主要由流纹岩、流纹质角砾凝灰熔岩、流纹质熔结(角砾)凝灰岩及少量角砾凝灰岩、火山角砾岩等组成，具有富硅、富碱、低铝、低钙特征，属于非造山偏碱性岩石，类似于大陆裂谷碱性流纹岩。研究表明，新生代陆相酸性火山岩为地壳岩石部分熔融作用的产物，形成于陆内拉张构造环境，与新生代早期渭河断裂带的左行走滑剪切构造作用有关。     

昆仑山与汶川强烈地震对青藏块体东北缘地壳运动及应变积累的影响

充分应用GPS、区域水准、跨断层等地形变观测资料, 借助非震负位错反演, 结合地震活动, 综合研究2001年11月14日昆仑山Ms8.1级地震对青藏块体东北缘地壳运动与应变积累的影响。通过分析笔者认为, 青藏块体内部Ms8.1级巨大地震能量释放产生的扰动应力场对NE向主压背景应力场的调制作用, 导致块体边界构造区域地壳差异运动和应力应变状态发生变化。其中, 对阿尔金断裂东段与祁连山断裂带西段的应变积累状态反映减缓为主的影响, 而对祁连山断裂带中东段则反映促进应变积累为主的影响。这种影响是一定时期、一定程度的。近期青藏块体东北缘区域应力场处于昆仑山、玉门、民乐等地震后的恢复状态。而由2008年5月12日汶川Ms8.0地震后有限的GPS、跨断层短水准观测资料, 可推测汶川地震对甘川交界东段-甘川陕交界区应变积累状况一定程度促进影响。     

大别山低级变质岩的构造背景

大别山南北两侧的浅变质岩是碰撞造山以前洋壳俯冲造山阶段的重要组成部分。木兰山片岩或张八岭群是俯冲的洋壳;苏家河群、信阳群和佛子岭群是由洋壳俯冲形成的海沟沉积,并因俯冲过程中的前进变形而形成增生楔;杨山煤系和梅山群是石炭纪弧前盆地沉积,并因俯冲过程中的前进变形而被增生楔逆掩。宿松群是扬子大陆被动边缘沉积,不是俯冲造山带的成员。因洋壳俯冲形成的弧和弧后盆地可能已被新生界沉积物掩盖。高压—超高压变质带是碰撞造山后期从深部折返的外来体。高压—超高压变质带正好处于洋壳和增生楔之间,破坏了早期洋壳俯冲造山带的完整性,使得洋壳俯冲造山阶段的特征被破坏,因而不易辨别。俯冲造山阶段应为奥陶纪到泥盆纪,碰撞造山阶段应从二叠纪开始。