Petrogenesis of Sierra Nevada plutons inferred from the Sr, Nd, and O isotopic signatures of mafic igneous complexes in Yosemite Valley, California

Mafic complexes in the central Sierra Nevada batholith record valuable geochemical information regarding the role mafic magmas play in arc magmatism and the generation of continental crust. In the intrusive suite of Yosemite Valley, major and trace element compositions of the hornblende-bearing gabbroic rocks from the Rockslides mafic complex and of the mafic dikes in the North America Wall are compositionally similar to high-alumina basalt. Of these rocks, two samples have higher Ni and Cr abundances as well as higher ε_Nd values than previously recognized for the intrusive suite. Plagioclase crystals in rocks from the North America Wall and the Rockslides have prominent calcic cores and sharply defined sodic rims, a texture commonly associated with mixing of mafic and felsic magmas. In situ analyses of ⁸⁷Sr/⁸⁶Sr in plagioclase show no significant isotopic difference from the cores to the rims of these grains. We propose that the high ⁸⁷Sr/⁸⁶Sr (~0.7067) and low ε_Nd (~?3.4) of bulk rocks, the homogeneity of ⁸⁷Sr/⁸⁶Sr in plagioclase, and the high δ¹⁸O values of bulk rocks (6.6–7.3 ‰) and zircon (Lackey et al. in J Petrol 49:1397–1426, 2008) demonstrate that continental crust was assimilated into the sublithospheric mantle-derived basaltic precursors of the mafic rocks in Yosemite Valley. Contamination (20–40 %) likely occurred in the lower crust as the magma differentiated to high-alumina basalt prior to plagioclase (and zircon) crystallization. As a consequence, the isotopic signatures recorded by whole rocks, plagioclase, and zircon do not represent the composition of the underlying lithospheric mantle. We conclude that the mafic and associated felsic members of the intrusive suite of Yosemite Valley represent 60–80 % new additions to the crust and include significant quantities of recycled ancient crust.     

Granitic rocks of Yosemite Valley and an ideal granite model

Stochastic models of an ideal, a degenerate ideal granite, and two models for metasomatically transformed granites have been compared with sequences of grains observed in granitic rocks of Yosemite Valley, California. Properties of the granitic rocks appear to show a relationship to the topography and stream directions, and may reflect the behavior of the granitic rocks with respect to fracturing and weathering.     

Oversized U-shaped canyon development at the edge of rotating blocks due to wrench faulting on margins of the Dead Sea graben

Strike-slip fault systems on the western margin of the Dead Sea active pull-apart basin (central part of the Dead Sea Transform) have been mapped in detail in the vicinity of the Ya'elim Valley, in the southeastern Judean Desert. Compressional, tensional and strike-slip shearing features are described and the geomorphology of the valley (which changes over a 6 km long segment from a mature meandering valley to a deep and narrow canyon, and then to an oversized, very deep and very wide U-shaped canyon), is elucidated using profiles and superimposed cross-sections. A kinematic model for the Formation of the Ya'elim Valley is proposed, reflecting dextral shearing on the margins of counterclockwise rotating blocks. In the same area Subrecent-Recent spreading of tensional fractures has occurred, separating sections of blocks which protrude eastward into the deepest on-land depression. The large-width of shear zones sub-perpendicular to the Transform may relate to repeated reversals in the sense of rotation of second-order (rigid block) domains, caused by rotations of neighbouring first order domains due to earthquake ruptures on individual parallel faults of the Transform.     

地质力学理论对中国深层油气勘查的作用

地质力学是我国著名地质科学家李四光创立的一门以系统论为基础,以构造体系为核心内容、跨学科的系统构造地质学理论。七十多年来,在区域地质、地震地质、地热勘查、第四纪地质、地壳稳定性评价等方面得到广泛的应用发展;在固体矿产、油气资源战略选区预测,指导部署勘探方面硕果累累。文章回顾了中国油气勘探历程,总结了地质力学理论在中国常规油气勘查思路和方法的成功经验,在松辽、塔里木及江汉等多个重要含油气盆地的发现中,地质力学理论起到了实用效果,并认为地质力学理论将一如既往,在我国深层油气勘查中继续发挥引领作用。      

Biostratigraphic and detrital zircon age constraints on the basement of the Himalayan Foreland Basin: Implications for a Proterozoic link to the Lesser Himalaya and cratonic India

The Himalayan Foreland Basin in the Ganga Valley is key to assessing the pre‐collision relationship between cratonic India and the Himalaya – the world's largest mountain chain. The subsurface Ganga Supergroup, representing the sedimentary basement of the Ganga Valley, has been interpreted as a northern extension of the Proterozoic Vindhyan Supergroup in cratonic India. This interpretation is contentious because the depositional age of the Ganga Supergroup is not resolved: whereas the lower Ganga Supergroup is widely regarded as Proterozoic, the upper Ganga Supergroup has been variously inferred to include Neoproterozoic, lower Palaeozoic, or Cretaceous strata. Here, we integrate biostratigraphic and detrital zircon data from drill cores to show that the entire Ganga Supergroup is likely Proterozoic and can be correlated with Proterozoic successions on the northern Indian craton and in the Lesser Himalaya. This helps redefine the first‐order stratigraphic architecture and indicates broad depositional continuity along the northern Indian margin during the Proterozoic.     

A Mid–Late Quaternary loess–paleosol record in Simmons Farm in southern Illinois,USA

In unglaciated areas of the Mississippi Valley region, the typical full loess–paleosol succession contains the Modern Soil developed in Peoria Silt, weakly developed Farmdale Geosol developed in Roxana Silt, Sangamon Geosol developed in Loveland Silt, and Yarmouth Geosol developed in Crowley's Ridge Silt. Although a fifth loess called the Marianna Silt is reported at one area, the paleosol that separates the Crowley Ridge and Marianna Silts is not well defined. Previous thermoluminescence (TL) and optical stimulated luminescence (OSL) age chronology has suggested multiple phases of Sangamon Geosol developed in Loveland Silt, but clear morphological evidence of polygenetic Sangamon Geosol profiles have not been found. Recently, a thick loess–paleosol sequence has been studied in the middle Mississippi Valley in unglaciated southern Illinois, USA. Soil morphology and analytical results revealed five loesses and associated paleosol units. Two Sangamon Bt horizons were found separated by a thick ACtk horizon, interpreted to indicate two phases of Sangamon Geosol development. This well-preserved loess–paleosol succession provides one of the most complete mid–late Quaternary loess records in the middle Mississippi Valley to date, and is important for studying the stratigraphic framework and paleoclimate and environment changes.     

Combining satellite and seismic images to analyse the shallow structure of the Dead Sea Transform near the DESERT transect

The left-lateral Dead Sea Transform (DST) in the Middle East is one of the largest continental strike-slip faults of the world. The southern segment of the DST in the Arava/Araba Valley between the Dead Sea and the Red Sea, called Arava/Araba Fault (AF), has been studied in detail in the multidisciplinary DESERT (DEad SEa Rift Transect) project. Based on these results, here, the interpretations of multi-spectral (ASTER) satellite images and seismic reflection studies have been combined to analyse geologic structures. Whereas satellite images reveal neotectonic activity in shallow young sediments, reflection seismic image deep faults that are possibly inactive at present. The combination of the two methods allows putting some age constraint on the activity of individual fault strands. Although the AF is clearly the main active fault segment of the southern DST, we propose that it has accommodated only a limited (up to 60 km) part of the overall 105 km of sinistral plate motion since Miocene times. There is evidence for sinistral displacement along other faults, based on geological studies, including satellite image interpretation. Furthermore, a subsurface fault is revealed ≈4 km west of the AF on two ≈E–W running seismic reflection profiles. Whereas these seismic data show a flower structure typical for strike-slip faults, on the satellite image this fault is not expressed in the post-Miocene sediments, implying that it has been inactive for the last few million years. About 1 km to the east of the AF another, now buried fault, was detected in seismic, magnetotelluric and gravity studies of DESERT. Taking together various evidences, we suggest that at the beginning of transform motion deformation occurred in a rather wide belt, possibly with the reactivation of older ≈N–S striking structures. Later, deformation became concentrated in the region of today’s Arava Valley. Till ≈5 Ma ago there might have been other, now inactive fault traces in the vicinity of the present day AF that took up lateral motion. Together with a rearrangement of plates ≈5 Ma ago, the main fault trace shifted then to the position of today’s AF.     

深部碳循环的环境气候效应SCIEI北大核心CSCD

地球表层温度主要由接收的太阳辐射能量及大气温室气体的保温能力共同控制。CO_(2)等温室气体通过对大气温度的调节影响着全球环境气候变化,工业革命以来全球CO_(2)排放量的增加被认为是全球变暖的重要原因,地质历史时期大气CO_(2)浓度的波动与温室和冰室气候的交替出现相对应。地球超过90%的碳赋存于深部,因此地球深部过程的些许波动便会影响到地表碳含量,进而深刻影响着地球的环境气候变化。以往的研究注重地表碳循环对环境气候的影响,对深部碳的贡献考虑不足。最近十余年全球开展了详细的深部碳循环研究,基于已经取得的重要成果,本文从大火成岩省、裂谷和俯冲带的视角对深部碳循环驱动的环境气候效应进行了系统回顾。认为未来的研究需要对地球深部碳循环通量和碳同位素组成进行更精确的定量,这是我们认识深部碳循环对地表环境气候影响的基础;除了碳元素本身我们还需要关注其他挥发性元素和有害金属元素的综合效应;俯冲带作为全球壳-幔相互作用和物质交换循环最重要的场所,应该是进行深部碳循环观察和环境气候效应研究的重点。     

Late Quaternary valley-fill succession of the Lower Tagus Valley, Portugal

The Lower Tagus Valley in Portugal contains a well-developed valley-fill succession covering the complete Late Pleistocene and Holocene periods. As large-scale stratigraphic and chronologic frameworks of the Lower Tagus Valley are not yet available, this paper describes facies, facies distribution, and sedimentary architecture of the late Quaternary valley fill. Twenty four radiocarbon ages provide a detailed chronological framework. Local factors affected the nature and architecture of the incised valley-fill succession. The valley is confined by pre-Holocene deposits and is connected with a narrow continental shelf. This configuration facilitated deep incision, which prevented large-scale marine flooding and erosion. Consequently a thick lowstand systems tract has been preserved. The unusually thick lowstand systems tract was probably formed in a previously (30,000–20,000 cal BP) incised narrow valley, when relative sea-level fall was maximal. The lowstand deposits were preserved due to subsequent rapid early Holocene relative sea-level rise and transgression, when tidal and marine environments migrated inland (transgressive systems tract). A constant sea level in the middle to late Holocene, and continuous fluvial sediment supply, caused rapid bayhead delta progradation (highstand systems tract). This study shows that the late Quaternary evolution of the Lower Tagus Valley is determined by a narrow continental shelf and deep glacial incision, rapid post-glacial relative sea-level rise, a wave-protected setting, and large fluvial sediment supply.     

Man-Made earthquakes Ein Weg zum Verständnis natürlicher seismischer Aktivität

The occurrence of earthquakes causing damage in regions, where no seismic activity had been observed previously, has confirmed the suspicion that the construction of high dams and pumped storage hydroelectric plants as well as the pressing of fluid into petroleum reservoirs and of waste water into deep boreholes will trigger the release of tectonic stresses in the earth's crust. A great number of examples indicates that a similar mechanism must be operative in all cases. Comparing the results of laboratory experiments to seismological observations, it is evident that the causes for the “loss of internal balance” must be sought in zones of low velocity and of relatively high energy absorption within the upper part of the earth's crust.     

Surface complexation modeling for predicting solid phase arsenic concentrations in the sediments of the Mississippi River Valley alluvial aquifer, Arkansas, USA

The potential health impact of As in drinking water supply systems in the Mississippi River Valley alluvial aquifer in the state of Arkansas, USA is significant. In this context it is important to understand the occurrence, distribution and mobilization of As in the Mississippi River Valley alluvial aquifer. Application of surface complexation models (SCMs) to predict the sorption behavior of As and hydrous Fe oxides (HFO) in the laboratory has increased in the last decade. However, the application of SCMs to predict the sorption of As in natural sediments has not often been reported, and such applications are greatly constrained by the lack of site-specific model parameters. Attempts have been made to use SCMs considering a component additivity (CA) approach which accounts for relative abundances of pure phases in natural sediments, followed by the addition of SCM parameters individually for each phase. Although few reliable and internally consistent sorption databases related to HFO exist, the use of SCMs using laboratory-derived sorption databases to predict the mobility of As in natural sediments has increased. This study is an attempt to evaluate the ability of the SCMs using the geochemical code PHREEQC to predict solid phase As in the sediments of the Mississippi River Valley alluvial aquifer in Arkansas. The SCM option of the double-layer model (DLM) was simulated using ferrihydrite and goethite as sorbents quantified from chemical extractions, calculated surface-site densities, published surface properties, and published laboratory-derived sorption constants for the sorbents. The model results are satisfactory for shallow wells (10.6 m below ground surface), where the redox condition is relatively oxic or mildly suboxic. However, for the deep alluvial aquifer (21-36.6 m below ground surface) where the redox condition is suboxic to anoxic, the model results are unsatisfactory.     

月球岩浆洋演化的实验岩石学研究进展SCIEI北大核心CSCD

由于缺少直接来自月球深部的岩石样品,实验和计算模拟是认识早期月球演化过程的有效方法和手段。20世纪70年代以来,陆续开展了大量的实验岩石学和实验地球化学工作对月球岩浆洋(lunar magma ocean,LMO)演化模型进行验证和修正。但是,学界对LMO模型中的两个关键性参数,即初始物质组成和熔融深度,仍然存在不同的认识。根据月震和重力探测数据推测的平均月壳厚度的差异、月球样品含水量的研究以及新的遥感数据解译发现月表广泛分布富镁铝尖晶石(Cr#<5)等等,直接影响我们对月球初始物质组成和LMO深度以及月球深部高压矿物相的评估。本文通过整理高温高压实验岩石学和实验地球化学在研究LMO演化方面的一系列研究成果,主要聚焦以下几个科学问题:(1)月球初始物质组成中的难熔元素和挥发分含量,以及LMO深度对月壳厚度、结晶矿物的种类及含量有着决定性的影响;(2)高压矿物相石榴子石在月球深部稳定存在的可能性及其对残余岩浆中微量元素的分配行为的制约;(3)特殊类型的月球样品(包括火山玻璃、镁质岩套等)的成因机制对月球深部物质组成具有指示意义;(4)月核的不同物质组成对LMO模型的初始成分含量,特别是微量元素的限定作用。我们以最新的观测数据和月球样品的分析结果为依据,对已有的LMO演化模型进行重新评估,提出月球深部含有石榴子石的LMO演化模型的可能性,并对该方向亟需开展的工作进行探讨。     

Dynamics and evolution of the deep mantle resulting from thermal,chemical, phase and melting effects

The core–mantle boundary (CMB) – the interface between the silicate mantle and liquid iron alloy outer core – is the most important boundary inside our planet, with processes occurring in the deep mantle above it playing a major role in the evolution of both the core and the mantle. The last decade has seen an astonishing improvement in our knowledge of this region due to improvements in seismological data and techniques for mapping both large- and small-scale structures, mineral physics discoveries such as post-perovskite and the iron spin transition, and dynamical modelling. The deep mantle is increasingly revealed as a very complex region characterised by large variations in temperature and composition, phase changes, melting (possibly at present and certainly in the past), and anisotropic structures. Here, some fundamentals of the relevant processes and uncertainties are reviewed in the context of long-term Earth evolution and how it has led to the observed present-day structures. Melting has been a dominant process in Earth's evolution. Several processes involving melting, some of which operated soon after Earth's formation and some of which operated throughout its history, have produced dense, iron rich material that has likely sunk to the deepest mantle to be incorporated into a heterogeneous basal mélange (BAM) that is now evident seismically as two large low-velocity regions under African and the Pacific, but was probably much larger in the past. This BAM modulates core heat flux, plume formation and the separation of different slab components, and may contain various trace-element cocktails required to explain geochemical observations. The geographical location of BAM material has, however, probably changed through Earth's history due to the inherent time-dependence of plate tectonics and continental cycles.     

地球中的流体和穿越层圈构造

地球中的流体是当前科学研究的重点。从地球科学的角度来说,流体应包括气体、液体（水和石油）、熔体和地球中受应力作用而移动的物体。在半经为6378 km的固体地球中可分为7个层圈。目前对地球内部流体的了解很少,为探索流体在各层圈中的成分,物理化学性质和分布,以现阶段对地球层圈和流体研究程度来看,其重点应放在地球中穿越层圈的构造部分和地壳。地球中穿越层圈的构造主要有三个:板块构造的俯冲带是由上到下的穿越层圈构造,向下俯冲的大洋岩石圈可以抵达地幔过渡带;大洋中脊的扩张引起的由下而上的穿越层圈构造,使岩石圈和地幔的熔流体从下向上运移;地幔柱引起的由下而上的穿越层圈构造,使地幔的熔流体从下向上迁移。通过对三个穿越层圈构造和地壳中流体的研究,可以得出地壳、岩石圈、上地幔、过渡带、下地幔和核幔边界层流体的种类和成分、流动和演化。这是至今为至能鉴定到地球中深部流体的方法。这四个方面的研究是当前地球中流体科学研究的重点,并对开展深部找矿有实际意义。      

Was There a Pliocene-Pleistocene Fluvial-Lacustrine Connection between Death Valley and the Colorado River?

Since the turn of the century, a Pliocene-Pleistocene connection between the Death Valley-Owens River pluvial system and the Colorado River drainage basin has been frequently postulated. The two most commonly proposed routes involve (1) a southward overflow from the Death Valley Lake system or (2) southward migration of the Mojave River between its present course and a more southerly route. Under the present topographic regime, a Death Valley Lake capable of overflowing the bedrock saddle at Ludlow, California and discharging southward into the Bristol, Cadiz, and Danby Lake basins (and eventually the Colorado River) would be over 12,000 km² in size. Few surface and subsurface indicators exist to support either a fluvial or lacustrine connection. Evidence from deep cores and boreholes drilled in Soda, Bristol, Cadiz, and Danby dry lake basins indicate that a hydrologic connection has not occurred during the past 4 myr. No well-documented paleoshoreline features have been located at elevations corresponding to the above hydrologic systems in Death Valley, Silver-Soda, Bristol, or Danby Lake basins. In the Cadiz, Silurian, and Broadwell basins these features have not been found at all. Therefore, we conclude that a hydrologic connection between the Death Valley-Owens River system and the Colorado River has not occurred along either of these routes since the middle Pliocene.     

东非裂谷Tanganyika地堑石油地质特征和勘探潜力分析

随着东非裂谷乌干达区块的勘探获得重大突破,与之石油地质条件相似的Tanganyika地堑的勘探潜力受到了人们的重视。Tanganyika地堑地处东非,属于东非裂谷西支的中段,是典型陆内裂谷盆地,主要沉积中新世以来的地层,现仍大部分被湖水覆盖,湖盆水体较深。盆地整体分为2个次盆,呈三隆夹两凹的构造格局。盆地目前勘探程度较低,根据现有资料推测,盆地地层埋深较大,深洼区中新统地层发育成熟烃源岩,具有较大的生烃潜力和生烃规模; 陆内盆地物源相对充足,储盖组合条件较好; 应力复杂,能够形成大量多种类型构造及构造-地层圈闭; 各种成藏条件匹配关系较好,有利于油气聚集成藏。综合分析认为,盆地具有较大勘探潜力,其中盆地转换带是最有利的油气勘探区。     

长江中下游成矿带庐枞矿集区新发现钨多金属矿床

庐枞矿集区是长江中下游成矿带内重要的铁铜矿集区,产出一系列典型的玢岩型铁矿床和斑岩型铜矿床。最近在庐枞矿集区北部东顾山地区,首次发现了钨多金属矿床,这是在长江中下游成矿带长江以北首次发现的钨矿化,为矽卡岩型。钨矿化主要呈浸染状或脉状产于东顾山岩体(黑云母花岗岩)与奥陶系(白云质灰岩)的接触带或大理岩层间破碎带中。矿石矿物主要为白钨矿及钼、铜、铅锌硫化物。钨矿化主要发育在华南地区,近年来在长江中下游成矿带的过渡带及以南的扬子地块如江南隆起等地发现多个新的大型钨矿床,但在长江以北地区一直未曾发现。庐枞矿集区北部东顾山钨矿床的发现,指明长江中下游成矿带燕山期除铁、铜大规模成矿作用以外,也有钨的成矿作用,指示该区具有良好的钨矿找矿前景。在长江中下游成矿带的其他矿集区要重视和加强钨矿化的成矿作用研究和找矿工作。     

Isotopic composition of formation waters from deep drillings in southern Israel

Formation water samples from deep drillings in southern Israel fall into three regional groups, each of which shows distinct chemical and isotopic characteristics. Waters from the Mediterranean coastal plain appear to be of marine lagoonal origin; some of these brines are associated with occurrences of oil. In the mountain region the top part of the sedimentary sequence has been flushed by fresher waters, apparently during Pleistocene time. In Jurassic and deeper-lying formations one encounters concentrated brines of seawater origin, with low Na/Ca ratios, which have undergone a process of ultrafiltration. In the Rift Valley proper, magnesium-rich brines have invaded the deeper formations, and are evidently of continental lake origin.The absence of oil occurrences in association with the CaCl₂ brines of the inland locations is interpreted as being due mainly to loss of oil as a result of the tectonic events associated with the formation of the Jordan Rift Valley.     

Large reactivated landslides in weak rock masses: a case study from the Northern Apennines (Italy)

This case study paper is about a large rotational rock and earth slide—earth flow located in the Secchia River Valley, in the Northern Apennines of Italy, that has displayed multiple reactivation phases between 2002 and 2004. The main geological constraints of the mass movement are related to the overlap of flysch rock masses over clayey complexes that allows rock slides to take place in the source area. The disarrangement and weathering of rock masses following slope movements causes large amount of fine-grained debris to be accumulated on the slope and mobilised by earth sliding and flowing. Analysis of rainfall data at the onset of reactivation events has proved that they occurred after periods with cumulated values higher than the averages of the last 30 years. The quantification of the morphological modifications induced by these reactivations has been made possible by comparing pre- and post-event digital elevation models. Depletion and accumulation has been in the range of 30 m in different parts of the slope. In particular, an advancement of the landslide toe of more than 400 m, which caused a 30-m thick landslide tip to deposit, has been clearly seen. Monitoring data regarding subsurface movements and surface tension crack widening (tension cracks so large as to be properly described at trenches) has shown that sliding surfaces as deep as 43 m exist in the upper part of the landslide, while the accumulation lobe has moved by sliding and flowing over surfaces as deep as some 10 m. Velocities of cm/day have been recorded in the deep surfaces and in widening trenches of the source area, while the advancement of the accumulation lobe has been estimated as having velocities of up to 10 m/day. Groundwater in the landslide body has been observed at depths of 5–15 m in the upper areas, while it is estimated as being at the ground level in the toe. On this basis, it is concluded that the landslide still has a high potential for further development, both in the upper landslide zone and in the toe area.     

Strontium Isotopic Signatures of the Streams and Lakes of Taylor Valley, Southern Victoria Land, Antarctica: Chemical Weathering in a Polar Climate

We have collected and analyzed a series of water samples from three closed-basin lakes (Lakes Bonney, Fryxell, and Hoare) in Taylor Valley, Antarctica, and the streams that flow into them. In all three lakes, the hypolimnetic waters have different ⁸⁷Sr/⁸⁶Sr ratios than the surface waters, with the deep water of Lakes Fryxell and Hoare being less radiogenic than the surface waters. The opposite occurs in Lake Bonney. The Lake Fryxell isotopic ratios are lower than modern-day ocean water and most of the whole-rock ratios of the surrounding geologic materials. A conceivable source of Sr to the system could be either the Cenozoic volcanic rocks that make up a small portion of the till deposited in the valley during the Last Glacial Maximum or from marble derived from the local basement rocks. The more radiogenic ratios from Lake Bonney originate from ancient salt deposits that flow into the lake from Taylor Glacier and the weathering of minerals with more radiogenic Sr isotopic ratios within the tills. The Sr isotopic data from the streams and lakes of Taylor Valley strongly support the notion documented by previous investigators that chemical weathering has been, and is currently, a major process in determining the overall aquatic chemistry of these lakes in this polar desert environment.