赣南地区石雷石英闪长岩的成因:岩石化学、副矿物微量元素、锆石U-Pb年代学与Sr-Nd-Hf同位素制约

石雷石英闪长岩是赣南崇-余-犹地区比较特殊的闪长质侵入体。锆石的原位U-Pb定年表明,该岩体侵位于433.5±3.4Ma。全岩主量元素特征上显示出中偏酸性(SiO2=56.92%～64.70%),富Al(Al2O3=14.10%～14.83%),富碱(Alk=6.41%～7.40%)特别是富钾(K2O=3.86%～4.85%),镁、铁含量较高,MgO:3.47%～5.95%,FeOT:5.23%～8.14%以及低磷(P2O5=0.27%～0.4%)的特点;微量元素上主要富集K、Rb、Cs等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti、P等高场强元素。磷灰石微量元素特征上显示高度富集稀土元素特别是轻稀土元素的特征;具有Eu的负异常(δEu=0.37～0.45)。ISr位于0.7073～0.7132之间,εNd(t)变化于-8.41～-4.97之间,两阶段钕模式年龄介于1.58～1.86Ga之间,Hf同位素组成相对均一,εHf(t)主要集中变化于-8～-2之间,两阶段Hf模式年龄加权平均为1.77±0.09Ga,这些特征都暗示了该石英闪长质岩体的形成是强烈壳幔相互作用的产物,区内加里东晚期可能发生了局部的岩石圈的减薄。     

Seismic velocities from the Yaquina forearc basin off Peru: evidence for free gas within the gas hydrate stability zone

Multichannel seismic (MCS) data from the Yaquina forearc basin off Peru reveal a complex distribution of gas and gas hydrate related reflections. Lateral variations of the reflection pattern at the assumed base of the gas hydrate stability zone in terms of continuity, amplitude, and signal attenuation underneath are observed, as well as the possible occurrence of paleo-bottom simulating reflectors (BSRs). Phase reversed reflections above the bottom simulating reflector point to free gas within the gas hydrate stability zone (GHSZ). To constrain the interpretation of the observed reflection pattern we calculated the velocity distribution along the MCS line from high-resolution ocean bottom hydrophone recordings with two independent methods. Heat flux values estimated on the basis of the velocity-depth functions increase with decreasing amplitude of the BSR and peak near chemoherms. These results suggest a model of the Yaquina Basin where free gas is trapped under parts of the BSR, and within the GHSZ, particularly under the seafloor and under an erosional unconformity. The hypothesis of a paleo-BSR that reflects the uplift of the base of the hydrate stability zone caused by the deposition of a particular sediment sequence is supported by the estimated heat flux values.     

西秦岭勉略带陆内构造变形研究

秦岭造山带勉略缝合带是古特提斯洋盆向北俯冲形成的华北与华南最后拼接带。这个主缝合带俯冲-碰撞过程中以由北向南的一系列韧性逆冲推覆构造为特征,形成由前泥盆系、泥盆-石炭系和蛇绿混杂岩等不同构造岩片叠置的复杂构造带,碰撞时代从245Ma一直延续到230Ma左右。最近,作者对勉略缝合带内发育的韧性和脆性左行走滑剪切变形进行了研究,结果表明这些顺造山带的左行韧性走滑剪切变形带的变形时代为223±2Ma,与碰撞后花岗岩所确定的碰撞后构造环境的起始时间(225Ma)一致,显示这些韧性走滑剪切变形带是勉略带陆内变形初期变形产物。亦即华北、扬子大陆碰撞之后很快就转入陆内变形阶段,并且是以顺造山带的侧向走滑位移为主要变形方式。勉略带内顺造山带的脆性左行走滑断层的发育,表明这种顺造山带的侧向位移过程从深部到地壳浅层是一致的。因此,大陆碰撞在直接碰撞之后很快转变为顺造山带的侧向走滑位移为主的陆内变形,这种位移可能表现为两个大陆碰撞后的相对走滑,或是碰撞带中强烈变形部分顺造山带的侧向挤出,从而消减了正向碰撞所造成的地壳缩短和增厚。     

西藏丁青弧前蛇绿岩的地球化学特征

丁青蛇绿岩位于班化湖－丁青－怒江蛇绿岩带的东段，其地幔岩出露规模是该带中最大的。本文报道的丁青蛇绿岩主要由地幔橄榄岩、堆晶岩、辉长岩和斜长花岗岩组成。蛇绿岩剖面上覆硅岩中的放射虫化石是早株罗世和晚三叠世诺利克期的，中侏罗统砂岩和砾岩不整合覆盖在蛇绿岩之上，由此确定丁青蛇绿岩是晚三叠－早侏罗世的，在中株罗世之前侵位，丁青蛇绿岩属于玻安岩系，玻安岩的特点是富Si、Mg和大离子亲石元素（LILE），贫高场强元素（Ti、P、Zr、Y、Yb和Nb）。丁青蛇绿岩的堆晶岩、辉长岩和辉绿岩均具“U”型REE分布，暗示丁青玻安岩是由于亏损的地幔源岩和来自消减带的水和流体两组分的混合形成的。丁青玻安岩的地球化学特征类似西太平洋第三纪玻安岩，而明显不同于MORB的地球化学性质， 表明丁青玻安岩应当形成于洋内岛弧的弧前环境，属于弧前蛇绿岩。     

Mapping mountain areas: learning from Global,European and Norwegian perspectives

Defining the spatial extent of mountain areas has long been a challenge. In the present century, the availability of digital elevation models(DEMs) incorporated into geographic information systems(GIS) has allowed the definition of mountain areas based on topographic and other criteria. This paper presents the various delineations of mountains that have been prepared at three scales – global, regional(Europe), and national – and explores the reasons and processes leading to these delineations, and how they have been used. A detailed case study is then presented for Norway. Overall, two types of approaches to mapping mountains have been taken: first, considering mountains per se, based on elevation and/or topography; second, considering them among other categories, e.g., landforms or biogeographical, environmental or landscape zones. All attempts to map mountain areas derive essentially from the objectives of those commissioning and/or undertaking the work; a unitary definition remains unlikely.     

The structural evolution of the Messinian evaporites in the Levantine Basin

The Levantine Basin in the South-eastern Mediterranean Sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load, because the Messinian evaporites are comparatively young, the sediment load varies along the basin margin, they are hardly tectonically overprinted, and the geometry of the basin and the overburden is well-defined. In this study we analyse depositional phases of the evaporites and their structural evolution by means of high-resolution multi-channel seismic data. The basinal evaporites have a maximum thickness of about 2 km, precipitated during the Messinian Salinity Crisis, 5.3–5.9 Ma ago. The evaporite body is characterized by 5 transparent layers sequenced by four internal reflections. We suggest that each of the internal reflection bands indicate a change of evaporite facies, possibly interbedded clastic sediments, which were deposited during temporal sea level rises. All of these internal reflections are differently folded and distorted, proving that the deformation was syn-depositional. Thrust angles up to 14° are observed. Backstripping of the Pliocene–Quaternary reveals that salt tectonic is mainly driven by the sediment load of the Nile Cone. The direction of lateral salt displacement is mainly SSW–NNE and parallel to the bathymetric trend. Apparent rollback anticlines off Israel result rather from differential subsidence than from lateral salt displacement. In the south-eastern basin margin the deposition of the Isreali Slump Complex (ISC) is coeval with the onset of salt tectonic faulting, suggesting a causal link between slumping processes and salt tectonics.

The superposition of ‘thin-skinned’ tectonics and ‘thick-skinned’ tectonics becomes apparent in several locations: The fold belt off the Israeli Mediterranean slope mainly results from active strike-slip tectonics, which becomes evident in faults which reach from the seafloor well below the base of the evaporites. Owing to the wrenching of the crustal segments which are bounded by deep-rooted fault lines like the Damietta–Latakia, Pelusium and Shelf Edge Hinge line the setting is transpressional south of 32°N, where the fault lines bend further towards the west. This adds a component of ‘thick-skinned’ transpression to the generally ‘thin-skinned’ compressional regime in the basin. Above 1.5 km of evaporites, a mud volcano is observed with the mud source seemingly within the evaporite layer. At the eastern Cyprus Arc, the convergence zone of the African and the Anatolian plates, deep-rooted compression heavily deformed the base of the evaporites, whereas at the Eratosthenes Seamount mainly superficial compression affecting the Post-Messinian sediments and the top of the evaporites is observed.     

Seasonal variations of the clear-sky greenhouse effect: the role of changes in atmospheric temperatures and humidities

We present an analysis of the factors which control the seasonal variations of the clear-sky greenhouse effect, based on satellite observations and radiative transfer simulations. The satellite observations include the radiation budget at the top of the atmosphere from the Earth Radiation Budget Experiment and the total column moisture content derived from the Special Sensor Microwave/Imager. The simulations were performed with the SAMSON system described in an earlier paper, using atmospheric temperatures and humidities from operational analyses produced by the European Centre for Medium Range Weather Forecasts. At low latitudes, the magnitude of the clear-sky greenhouse effect is dominated by the strong thermodynamic link between the total column moisture content of the atmosphere and sea surface temperatures, with minimal seasonal variations. In contrast, at middle to high latitudes there are strong seasonal variations, the clear-sky greenhouse effect being largest in winter and smallest in summer. These variations cannot be explained by the seasonal cycle in the total column moisture content, as this is largest in summer and smallest in winter. The variations are controlled instead by the seasonal changes in atmospheric temperatures. The colder atmosphere in winter enhances the temperature differential between the atmosphere and the sea surface, leading to a larger greenhouse effect despite the lower moisture contents. The magnitude of the clear-sky greenhouse effect is thus controlled by atmospheric humidity at low latitudes, but by atmospheric temperature at middle and high latitudes. These controls are illustrated by results from sensitivity experiments with SAMSON and are interpreted in terms of a simple model.     

The Levantine Basin—crustal structure and origin

The origin of the Levantine Basin in the Southeastern Mediterranean Sea is related to the opening of the Neo-Tethys. The nature of its crust has been debated for decades. Therefore, we conducted a geophysical experiment in the Levantine Basin. We recorded two refraction seismic lines with 19 and 20 ocean bottom hydrophones, respectively, and developed velocity models. Additional seismic reflection data yield structural information about the upper layers in the first few kilometers. The crystalline basement in the Levantine Basin consists of two layers with a P-wave velocity of 6.0–6.4 km/s in the upper and 6.5–6.9 km/s in the lower crust. Towards the center of the basin, the Moho depth decreases from 27 to 22 km. Local variations of the velocity gradient can be attributed to previously postulated shear zones like the Pelusium Line, the Damietta–Latakia Line and the Baltim–Hecateus Line. Both layers of the crystalline crust are continuous and no indication for a transition from continental to oceanic crust is observed. These results are confirmed by gravity data. Comparison with other seismic refraction studies in prolongation of our profiles under Israel and Jordan and in the Mediterranean Sea near Greece and Sardinia reveal similarities between the crust in the Levantine Basin and thinned continental crust, which is found in that region. The presence of thinned continental crust under the Levantine Basin is therefore suggested. A β-factor of 2.3–3 is estimated. Based on these findings, we conclude that sea-floor spreading in the Eastern Mediterranean Sea only occurred north of the Eratosthenes Seamount, and the oceanic crust was later subducted at the Cyprus Arc.