Neoglacial chronology and floristics in the Middle Teton area,central Teton Range,Western Wyoming

The relative ages of Neogfacial deposits above 2900m near Cloudveil Dome, Middle Teton, and Teepe glaciers, central Teton Range, western Wyoming, were determined using topographic position, weathering features, lichenometry, vegetation characteristics, and soils. A three-fold deposit sequence is identified and correlated with the Gannett Peak, Audubon and Indian Basin Neoglacial advances described elsewhere in the Teton and nearby Wind River ranges. While soil profile morphology proved very useful in distinguishing deposits of different age, other age indicators such as clay mineralogy and soil chemistry, proved of only marginal value in age discrimination. This chronosequence, emplaced over the last ～5000yr, provides an excellent setting upon which to test changes in plant species composition and its use as a relative dating method. Vascular plant species composition cannot be used to discriminate deposits of the different advances, possibly because of random colonisation and establishment combined with extensive mass wasting during the Neoglacial. However, certain vegetation features, such as total cover and species densities, appear useful as relative dating methods.     

New constraints on Holocene uplift rates for the Baudo Mountain Range,northwestern Colombia

A beach deposit on the southern end of the Baudo Mountain Range, at an elevation of ∼2.0 m above the backshore of the modern beach, was dated at ∼2870 years using optically stimulated luminescence dating. The calculated average uplift rate necessary to raise this deposit is 0.7 mm/yr. This rate combines the long-term regional deformation associated with the subduction of the Nazca Plate under the South American Plate and the collision of the Choco Block microplate against the South American continent, as well as uplift from local faults. We propose that rapid emergence probably as several pulses, each involving decimeter scale coseismic uplift, is likely to have occurred to elevate the beach above the intertidal zone and offset destructive wave erosion.     

Marra Mamba Iron Formation stratigraphy in the eastern Chichester Range,Western Australia

The Marra Mamba Iron Formation is the basal member of the Hamersley Group in Western Australia and is host to major iron‐ore deposits in its upper Mt Newman Member. Previous studies have suggested that the Marra Mamba Iron Formation in the eastern Chichester Range was deposited in an isolated basin behind a barrier reef and was greatly reduced in thickness. New drilling covering a large part of the Chichester Range shows that only the lower part of the Nammuldi Member, the lowest unit of the Marra Mamba Iron Formation, remains over most of the range. However, 15 m of the Mt Newman Member, the complete MacLeod Member and the upper part of the Nammuldi Member were drilled in small north‐south synclines preserved near Mulga Downs homestead. This drilling shows that the Marra Mamba Iron Formation is similar in all respects to other occurrences in the Hamersley Province. There is no evidence of facies change or reduced thickness and therefore no evidence for a northern limit to the deposition of the Hamersley Group. Apart from the small synclines near Mulga Downs homestead, the Fortescue River alluvial deposits abutting the Chichester Range are underlain by the Roy Hill Shale Member of the Jeerinah Formation.     

Geomorphic constraints on the Late Neogene tectonics of the Otway Range,Victoria

A Pliocene strandline system in the Hanson Plain Sands, between the volcanic plains of the Western District and the northern flanks of the Otway Range in southwest Victoria, provides an excellent datum against which to measure Late Neogene fault‐related uplift. Individual strandlines that can be traced from elevations of ～120 m near Cobden to ～245 m on the Ferguson Hill structure are displaced across northeast‐trending faults and monoclines associated with the Simpson and Ferguson Hill structures. A break in slope in the Otway Range front at elevations of 230–280 m, beneath which drainage incision parallels the trends of the strandlines, probably correlates with the Pliocene coastline on the ancestral Otway Range. By analogy with correlative systems in the Murray Basin, deposition occurred during sea‐stands between 0 and 65 m above present‐day sea‐level, implying uplift of between 175 and 240 m since the Early Pliocene. Enhanced incision parallel to the strandlines, in combination with tilting of fault blocks about northeast axes at a high angle to the strandlines, has facilitated the development of a remarkable rectilinear drainage net. Local inversion of the drainage where it focused basalt flows constrains the age of incision and faulting to greater than ca 1 Ma and, most probably, less than ca 2 Ma.     

A Periglacial Palaeoenvionment in the Upper Carboniferous–Lower Permian Tobra Formation of the Salt Range, Pakistan

The Upper Carboniferous—Lower Permian(Upper Pennsylvanian-Asselian) Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan.The formation exhibits an alluvial plain(alluvial fan-piedmont alluvial plain) facies association in the Salt Range and Khisor Range.In addition,a stream flow facies association is restricted to the eastern Salt Range.The alluvial plain facies association is comprised of clast-supported massive conglomerate(Gmc),diamictite(Dm)facies,and massive sandstone(Sm) Hthofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and siltstone(Fss),fining upwards pebbly sandstone(Sf),and massive mudstone(Fm) Hthofacies.The lack of glacial signatures(particularly glacial grooves and striatums) in the deposits in the Tobra Formation,which are,in contrast,present in their timeequivalent and palaeogeographically nearby strata of the Arabian peninsula,e.g.the AI Khlata Formation of Oman and Unayzah B member of the Saudi Arabia,suggests a pro-to periglacial,i.e.glaciofluvial depositional setting for the Tobra Formation.The sedimentology of the Tobra Formation attests that the Salt Range,Pakistan,occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time.     

The interplay of fold mechanisms and basement weaknesses at the transition between Laramide basement-involved arches, north-central Wyoming, USA

Horizontally-shortened, basement-involved foreland orogens commonly exhibit anastomosing networks of bifurcating basement highs (here called arches) whose structural culminations are linked by complex transition zones of diversely-oriented faults and folds. The 3D geometry and kinematics of the southern Beartooth arch transition zone of north-central Wyoming were studied to understand the fold mechanisms and control on basement-involved arches.Data from 1581 slickensided minor faults are consistent with a single regional shortening direction of 065°. Evidence for oblique-slip, vertical axis rotations and stress refraction at anomalously-oriented folds suggests formation over reactivated pre-existing weaknesses. Restorable cross-sections and 3D surfaces, constrained by surface, well, and seismic data, document blind, ENE-directed basement thrusting and associated thin-skinned backthrusting and folding along the Beartooth and Oregon Basin fault systems. Between these systems, the basement-cored Rattlesnake Mountain backthrust followed basement weaknesses and rotated a basement chip toward the basin before the ENE-directed Line Creek fault system broke through and connected the Beartooth and Oregon Basin fault systems. Slip was transferred at the terminations of the Rattlesnake Mountain fault block by pivoting to the north and tear faulting to the south. In summary, unidirectional Laramide compression and pre-existing basement weaknesses combined with fault-propagation and rotational fault-bend folding to create an irregular yet continuous basement arch transition.     

Orientation,composition, and entrapment conditions of fluid inclusions in the footwall of the northern Snake Range detachment,Nevada

Footwall rocks of the northern Snake Range detachment fault (Hampton and Hendry's Creeks) offer exposures of quartzite mylonites (sub-horizontal foliation) that were permeated by surface fluids. An S–C–C′ mylonitic fabric is defined by dynamically recrystallized quartz and mica. Electron backscatter diffraction analyses indicate a strong preferred orientation of quartz that is overprinted by two sets of sub-vertical, ESE and NNE striking fractures. Analyses of sets of three perpendicular thin sections indicate that fluid inclusions (FIs) are arranged according to macroscopic fracture patterns. FIs associated with NNE and ESE-striking fractures coevally trapped unmixed CO₂ and H₂O-rich fluids at conditions near the critical CO₂–H₂O solvus, giving minimum trapping conditions of T = 175–200 °C and ∼100 MPa H₂O-rich FIs trapped along ESE-trending microcracks in single crystals of quartz may have been trapped at conditions as low as 150 °C and 50 MPa indicating the latest microfracturing and annealing of quartz in an overall extensional system. Results suggest that the upper crust was thin (4–8 km) during FI trapping and had an elevated geotherm (>50 °C/km). Footwall rocks that have been exhumed through the brittle-ductile transition in such extensional systems experience both brittle and crystal-plastic deformation that may allow for circulation of meteoric fluids and grain-scale fluid–rock interactions.     

大兴安岭地幔橄榄岩中熔体的多样性及其成因

本文报道了大兴安岭第四纪火山岩中的地幔橄榄岩中橄榄石、单斜辉石和斜方辉石颗粒内部熔体产状(囊体、包裹体和反应边)和成分(低硅熔体和高硅熔体)的多样性,初步讨论了不同熔体的成因。低硅熔体囊体是在地幔深部玄武岩浆与橄榄岩中单斜辉石发生交代反应的产物,斜方辉石反应边的高硅熔体是橄榄岩被捕获上升过程中玄武岩浆与斜方辉石反应的产物,高硅熔体包裹体是地幔中存在的交代熔体。     

念青唐古拉花岗岩热演化历史和山脉隆升过程的热年代学分析

念青唐古拉山是青藏高原内部的重要山脉,主体由黑云母二长花岗岩组成,岩体内部发育不同类型的变质岩包体如Lgn、Ygn片麻岩和元古代（Pt）变质岩,岩体东西两侧发育伸展型韧性剪切带。对念青唐古拉黑云母二长花岗岩进行矿物对热年代学分析,良好地揭示了岩浆热演化历史和山脉隆升过程。通过单颗粒锆石离子探针测年,发现65．0～55．0Ma发生早期岩浆侵位事件,形成Lgn、Ygn花岗片麻岩包体;在18．3～11．1Ma期间,在约11km深度的Lgn、Ygn下方发生大规模岩浆侵位和结晶成岩事件,形成念青唐古拉黑云母二长花岗岩（NG）。在11．1～9．3Ma期间,念青唐古拉花岗岩发生快速冷却和隆升过程,平均降温速度约222．2℃／Ma,对应的平均差异隆升速率为5．56mm／a;在9．3～8．6Ma期间,念青唐古拉花岗岩继续发生差异隆升和快速降温,平均降温速率为142．8℃／Ma,对应的差异隆升速率为3．57mm／a;在8．0～5．0Ma期间,念青唐古拉山区发生伸展型韧性剪切变形,导致念青唐古拉花岗岩快速隆升,平均差异隆升速率为3．50mm／a;在5．0～3．7Ma期间,念青唐古拉花岗岩继续发生构造隆升,平均降温速率约92．3℃／Ma,对应的平均差异隆升速率为2．31mm／a。自3．7Ma以来念青唐古拉花岗岩平均降温速度达27．0℃／Ma,平均抬升速度达0．68mm／a。念青唐古拉岩浆集聚、NG花岗岩侵位与INDEPTH-Ⅱ地震深反射亮点揭示的地壳局部熔融存在动力学成因联系,导致上地壳伸展构造变形、NG花岗岩缓慢冷却和念青唐古拉山脉快速隆升。     

喀喇昆仑山厦呈、吕莫慕士塔格山段现代冰川分布及变化特征

在全球气候普遍变暖、冰川大面积退缩的大背景下,为揭示山岳冰川十分发育的喀喇昆仑山脉现代冰川分布及变化特征,以中等空间分辨率(ETM和Landsat 8)卫星数据为主要数据源,采用人机交互式解译方法完成了厦呈慕士塔格山、吕莫慕士塔格山段冰川变化遥感调查,基本查明了区内冰川面积、分布特征和变化状况,共调查1 373处冰川,其中中国境内有554处,境外克什米尔印控区有819处; 同时对区内典型冰川变化进行了2期对比分析,得出冰舌退缩、前进或稳定现象同时存在的结论,为喀喇昆仑山脉冰川变化研究提供了参考依据,为我国西部边海防地区水资源的开发利用和冰雪灾害的防治等提供了科学依据。     

Holocene vegetation, fire and climate history of the Sawtooth Range, central Idaho, USA

The paucity of low- and middle-elevation paleoecologic records in the Northern Rocky Mountains limits our ability to assess current environmental change in light of past conditions. A 10,500-yr-long vegetation, fire and climate history from Lower Decker Lake in the Sawtooth Range provides information from a new region. Initial forests dominated by pine and Douglas-fir were replaced by open Douglas-fir forest at 8420 cal yr BP, marking the onset of warmer conditions than present. Presence of closed Douglas-fir forest between 6000 and 2650 cal yr BP suggests heightened summer drought in the middle Holocene. Closed lodgepole pine forest developed at 2650 cal yr BP and fires became more frequent after 1450 cal yr BP. This shift from Douglas-fir to lodgepole pine forest was probably facilitated by a combination of cooler summers, cold winters, and more severe fires than before. Five drought episodes, including those at 8200 cal yr BP and during the Medieval Climate Anomaly, were registered by brief intervals of lodgepole pine decline, an increase in fire activity, and mistletoe infestation. The importance of a Holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago.     

准噶尔盆地西北部P-T转换期不整合的发育演化特征及意义*

二叠纪晚期—三叠纪早期是准噶尔盆地演化的重要转换期,发育了具有特色性的不整合面。本研究以该盆地的西北部为例,综合利用地震和钻井资料,探讨该时期不整合的发育演化特征及其地质意义。研究表明,转换期发育P₃/P₂期主要不整合与T₁/P₃期次要不整合,它们在研究区北部叠加复合,构成了三叠系底界叠合不整合面,在南部被上二叠统所分隔而独立存在;转换期经历了主要不整合的形成、主要不整合被上二叠统超覆、次要不整合与叠合不整合的形成及其被三叠系最终超覆4个演化阶段。不整合的发育演化特征揭示了晚海西期和早印支期构造运动对准噶尔盆地影响的强弱程度、地层记录的“楔形体”内涵以及上二叠统与下三叠统的层序归属。P-T转换期不整合面及其相邻地层形成了有效的油气运移通道、良好的储盖组合和类型众多的圈闭,因此具有重要的油气勘探意义。     

鄂尔多斯盆地早侏罗世富县期沉积演化: 大洋缺氧事件前后陆地气候变化的响应*

托阿尔期早期早侏罗世大洋缺氧事件(T-OAE,~183.8 Ma)是一次全球性的地质事件,鄂尔多斯盆地下侏罗统富县组记录了此次地质事件的陆地响应过程。主要基于盆地东缘野外地质调查、扫描电镜及薄片分析,本次研究描述了盆地东北部富县组岩性、颜色和沉积序列,利用前人研究成果总结了富县期岩相古地理变化规律及沉积模式,认为富县期经历了由干旱到湿润的古气候变化: 富县组下部含植物化石较为丰富的白色砂砾岩及黑色、灰色泥页岩沉积于湿润气候时期,对应着盆地下切河谷发育期和填平补齐期; 而上覆的罕见植物化石的杂色、红色泥页岩为(富县期晚期)相对平坦地形条件下的沉积,对应着早、中侏罗世湿润气候背景下的一次干旱气候脉动,为托阿尔期大洋缺氧事件在陆相环境的气候响应,可由此进行富县组区域等时性对比。研究认为“粗富县”为下切谷内河流充填沉积, “细富县”形成于湖泊环境或河漫环境, “黑富县”和“白富县”是湿润气候条件下沉积产物,而“红富县”和“杂富县”为T-OAE期后干旱条件下形成。     

大兴安岭北段新林地区战备村组火山岩地球化学特征及构造环境

大兴安岭北段新林地区下侏罗统战备村组火山岩岩石组合主要为流纹岩、流纹质火山碎屑岩。岩石地球化学研究显示,流纹岩具有高硅、富碱、贫钙镁的特征,属于高钾钙碱性系列。火山岩稀土元素总量较低（ΣREE=81.84×10-6~110.32×10-6）,轻、重稀土元素分馏明显,（La/Yb）N值为21.57~40.21,中等负Eu异常,δEu值为0.42~0.62。岩石富集大离子亲石元素Rb、K、Th、U,亏损高场强元素Nb、Ta、P、Ti,基性相容元素Cr、Co、Ni和Mg#值均较低,具有壳源岩浆的特点。流纹岩Sr、Yb值较低,具有喜马拉雅型花岗岩的特征。结合区域早侏罗世火山岩的构造特征,认为战备村组火山岩形成于蒙古-鄂霍茨克洋SE向俯冲的构造环境。     

大兴安岭北段呼中西部塔木兰沟组火山岩年代学、岩石地球化学特征及其构造意义

呼中火山岩位于大兴安岭北段,塔木兰沟组是其喷发较早的一期中基性火山岩。锆石U-Pb年代学研究表明,呼中火山岩形成于(154±1)Ma,属晚侏罗世。呼中火山岩SiO_2为49.80%~55.96%、Al_2O_3为16.70%~18.93%、Na_2O+K_2O为6.35%~9.11%,属中基性高铝碱性岩石。微量元素特征显示,呼中火山岩富集大离子亲石元素Ba,亏损高场强元素Nb、Ta,Nb/Ta=12.44~15.58。呼中火山岩元素含量及其比值的变化显示了本区塔木兰沟组玄武岩浆在分离结晶作用过程中受到了壳源物质的影响,其形成环境为板块边缘岛弧造山带环境,由古亚洲洋和(或)蒙古—鄂霍茨克洋板块俯冲形成。     

Analysis of the geometric characteristics of clinothems and the relationship with shelf-edge trajectories of the Plio-Pleistocene continental slope in the Qiongdongnan Basin,South China Sea

Based on high-quality two-dimensional seismic profiles and well data, the seismic reflection characteristics from the late Pliocene and Pleistocene succession of the Qiongdongnan Basin in the South China Sea have been analysed. The result will help in understanding the sedimentological development of slope areas. Twenty coeval clinothems are recognized and four major clinothem types are distinguished. In addition, three types of shelf-edge trajectories are recognized. The various parameters of the clinothems are analysed quantitatively and the relationships between the various clinothem types are studied in combination with the controlling roles. It is concluded that: (i) the shelf-edge trajectories are related to the type of clinothem; (ii) fluctuations in the relative sea level, in combination with variations in sediment supply, result in different clinothem types and geometric parameters; these parameters show interdependencies; (iii) the alternations of progradation and aggradation of clinothems may provide information of the relative sea level and changes in sediment supply; (iv) some lowstand fans could develop at the foot of the slope in the central–eastern part of the basin when the relative sea level started to fall or began to rise. The results of the present study are consequently significant for further quantitative analyses of the characteristics and development of the continental slope, not only in the Qiongdongnan Basin, but also in other basins.     

唐古拉地区拉卜查日组牙形石的发现、锶同位素组成及地层学意义

首次在唐古拉地区晚二叠世—早三叠世拉卜查日组中获得牙形石化石,其分子为Hindeodus typicalis、H.eurypyge和H.praeparvus。根据其地层意义并结合层序地层学及海平面变化研究,最终将研究区二叠系与三叠系界线的可能位置定在实测剖面的29层顶、30层底。基于此,作者系统测试了拉卜查日组中的碳酸盐岩87Sr/86Sr比值,结果表明,二叠系/三叠系界线附近87Sr/86Sr比值为0.707017~0.707032,显著小于国内外其他地区二叠系/三叠系界线附近87Sr/86Sr比值。造成这种差异的主要原因,可能是由于唐古拉地区二叠系/三叠系界线附近存在广泛的火山活动以及上扬子地区二叠纪广泛的玄武岩喷发等地方性事件。此外,剖面上锶同位素演化曲线与海平面变化曲线对比显示,87Sr/86Sr比值的最小值与初始海泛面基本一致,锶同位素演化曲线与海平面变化曲线有着很好的一致性,说明全球海平面变化是其最主要的控制因素。     

大兴安岭中部柴河地区晚侏罗世花岗质岩石成因及构造意义

本文对大兴安岭中部柴河地区晚侏罗世花岗质岩石进行了岩石学、同位素年代学、地球化学等研究,探讨了其岩石成因及形成的构造背景。岩石学研究表明,大兴安岭中部柴河地区晚侏罗世花岗质岩石主要岩石组合为花岗闪长岩、二长花岗岩和碱长花岗岩。LA-ICP-MS锆石U-Pb测年结果获得2个二长花岗岩年龄分别为（152±1）Ma和（150±1）Ma。岩石主量元素具有富钾钠、富铝的特点,属铁质碱-钙性岩石。稀土元素相对富集轻稀土元素、亏损重稀土元素,具有弱到中等的Eu负异常,微量元素主要富集大离子亲石元素（Rb、Th、U、K、LREE）和Zr、Hf元素,亏损高场强元素（Nb、Ta、P、Ti）和Ba、Sr元素。地球化学特征指示这些晚侏罗世花岗质岩石来源于新元古代和早古生代期间从亏损地幔新增生的地壳物质部分熔融,形成于蒙古-鄂霍茨克洋闭合陆壳加厚之后挤压到伸展的转换环境。     

南非巴伯顿绿岩带条带状铁建造岩石磁学及磁性矿物的组成特征

条带状铁建造(BIFs)中含有大量的亚铁磁性矿物,其组成及来源是认识BIF成因的重要依据。本文研究了南非巴伯顿绿岩带无花果树群(距今约32亿年)恩圭尼亚组的BIFs样品的磁学和矿物学特征。通过测量富铁层与富硅层的磁滞回线、等温剩磁获得曲线与退磁曲线、矫顽力谱分析、一阶反转曲线(FORC)、低温(20～300K)有场/无场冷却曲线以及k-T曲线、Lowrie三轴热退磁曲线,结合扫描电镜观测,揭示出研究样品中磁性矿物主要为赤铁矿和磁铁矿。基于矫顽力谱分析,富铁层中磁铁矿主要是多畴及假单畴颗粒,相对含量平均为2. 1%;赤铁矿的相对含量平均为97. 9%。富硅层中磁铁矿主要为假单畴及超顺磁性颗粒,相对含量平均为4. 6%;赤铁矿相对含量平均为95. 4%。测试样品具有Morin转变特征,转变温度介于250～260K,说明BIFs中主要为赤铁矿(0. 5～6mm)。富硅层样品出现～107K、～125K两个Verwey转变温度,表明其中可能存在生物成因和非生物成因两种类型磁铁矿。     

大兴安岭北段高地林场满克头鄂博组火山岩年代学、地球化学特征及其构造意义

对大兴安岭北段高地林场地区满克头鄂博组火山岩进行LA-ICP-MS锆石U-Pb定年和岩石地球化学研究,以限定其岩石成因及成岩构造背景.定年结果显示:火山岩年龄为(149±1)Ma,形成于晚侏罗世.岩石地球化学特征具有高硅、富碱、贫钙、贫镁,为高钾钙碱性弱过铝质岩石;稀土总量(ΣREE)为124.32×10-6～189....