黑龙江省铜山斑岩铜矿床流体包裹体研究

铜山大型铜矿床位于小兴安岭西北部,是中亚-兴蒙造山带北东段最著名的斑岩型铜矿床之一,矿体产于加里东期花岗闪长岩和中奥陶世多宝山组安山岩、凝灰岩中,铜矿化与硅化-绢云母化关系密切.流体包裹体研究表明,铜山铜矿床主要发育气液两相包裹体、含CO_2包裹体和含子矿物多相包裹体.成矿流体在形成过程中经历了早、中、晚3个阶段的演化.成矿早阶段发育气液两相水溶液包裹体和少量含子矿物多相包裹体,均一温度介于420℃～＞5500C之间,流体盐度介于13.72 wt%～59.76 wt%NaCl eqv之间;中阶段为铜山矿床的主成矿阶段,发育气液两相水溶液包裹体和含CO_2包裹体,均一温度为241℃～417℃,流体盐度介于2.96 wt%～14.04 wt%NaCl eqv之间,主成矿期成矿流体总体上属H_2O-CO_2-NaCl体系;晚阶段仅发育气液两相水溶液包裹体,均一温度为122℃～218℃,盐度介于3.71 wt%～15.96 wt%NaCl eqv之间,表明晚阶段有大气降水的混入.成矿早、中阶段的流体均为不混溶流体,流体沸腾作用是金属硫化物大量沉淀的主要机制.铜山矿床形成于陆缘弧环境.     

兰州皋兰山黄土滑坡特征及灾度评估研究

皋兰山滑坡是西北地区非常典型的黄土滑坡,由3个次级滑坡构成,形成条件可概括为:新构造作用促使皋兰山强烈隆起,形成高达200～300m以上陡峻的自然斜坡,平均坡度在33.7°,临空条件好;构成斜坡的基岩为泥岩,其上覆盖很厚的黄土层,泥岩表面风化、破碎严重,不透水,黄土垂直节理发育,有利于地表水的渗入,在黄土与泥岩的接触面构成抗剪强度低值带;在地下水对下部软弱层侵润作用下,其抗剪强度大大降低;地震是促使滑坡产生的突发因素;同时,由于斜坡前缘建房开挖边坡及公园建设加载和绿化灌溉等,导致坡体稳定性明显降低,出现失稳破坏。通过野外勘查和位移监测及稳定性计算表明:目前滑坡总体上处于稳定状态,局部滑坡体复活变形迹象渐趋明显,其中变形最严重的是位于斜坡中下部并紧邻市区的Ⅰ3滑坡、Ⅰ4滑坡和Ⅲ滑坡。文章还对滑坡潜在损失进行了初步评估,并提出了防治方案和建议。     

Hydrogeology of desert springs in the Panamint Range,California, USA: Geologic controls on the geochemical kinetics,flowpaths, and mean residence times of springs

Over 180 springs emerge in the Panamint Range near Death Valley National Park, CA, yet, these springs have received very little hydrogeological attention despite their cultural, historical, and ecological importance. Here, we address the following questions: (1) which rock units support groundwater flow to springs in the Panamint Range, (2) what are the geochemical kinetics of these aquifers, and (3) and what are the residence times of these springs? All springs are at least partly supported by recharge in and flow through dolomitic units, namely, the Noonday Dolomite, Kingston Peak Formation, and Johnnie Formation. Thus, the geochemical composition of springs can largely be explained by dedolomitization: the dissolution of dolomite and gypsum with concurrent precipitation of calcite. However, interactions with hydrothermal deposits have likely influenced the geochemical composition of Thorndike Spring, Uppermost Spring, Hanaupah Canyon springs, and Trail Canyon springs. Faults are important controls on spring emergence. Seventeen of twenty-one sampled springs emerge at faults (13 emerge at low-angle detachment faults). On the eastern side of the Panamint Range, springs emerge where low-angle faults intersect nearly vertical Late Proterozoic, Cambrian, and Ordovician sedimentary units. These geologic units are not present on the western side of the Panamint Range. Instead, springs on the west side emerge where low-angle faults intersect Cenozoic breccias and fanglomerates. Mean residence times of springs range from 33 (±30) to 1,829 (±613) years. A total of 11 springs have relatively short mean residence times less than 500 years, whereas seven springs have mean residence times greater than 1,000 years. We infer that the Panamint Range springs are extremely vulnerable to climate change due to their dependence on local recharge, disconnection from regional groundwater flow (Death Valley Regional Flow System - DVRFS), and relatively short mean residence times as compared with springs that are supported by the DVRFS (e.g., springs in Ash Meadows National Wildlife Refuge). In fact, four springs were not flowing during this campaign, yet they were flowing in the 1990s and 2000s.     

Geomorphology and seismotectonic elements in the giarre area,sicily

A morphostructural analysis has been performed on the eastern flank of Mt Etna, located between the towns of St. Alfio and Linera and the Ionian Sea. The research has been carried out through analysis of aerial photographs, and has allowed recognition of morphoneotectonic elements such as: some scarps with rectilinear trend, laterally becoming morphological flexures, according to the lithology; anomalies in the hydrographic network, such as rectilinear tracts of drainage, valleys with simple or double bends, hanging valleys and truncated valleys, narrow deeply engraved valleys with meanders and fluvial captures. All these elements are caused by a fault system oriented NNW–SSE, with a mainly vertical component. Seismic events with very shallow foci have been recorded in the study area; these earthquakes triggered several small landslides on the fault scarps and large series of coseismic and coaxial fractures. It is possible to show that the morphostructures examined have been reactivated during many of the seismic events that have occurred in the area. The combination of these elements verifies that the morphostructures have a real neotectonic cause, which is associated with uplifts which have occurred in the area at different times.     

Shear-wave polarizations in the Peter the First Range indicating crack-induced anisotropy in a thrust-fault regime

Summary. Three-component seismograms of small local earthquakes recorded in the Peter the First Range of mountains near Garm, Tadzhikistan SSR, display shear-wave splitting similar to that previously observed near the North Anatolian Fault in Turkey. The Peter the First Range is in a region of compressional tectonics, whereas the North Anatolian Fault is a comparatively simple strike-slip fault. Detailed analysis of the Turkish records suggests that the splitting is diagnostic of crack-induced anisotropy caused by vertical microcracks aligned parallel to the direction of maximum compression. Preliminary examination of paper records from Garm shows that most shear waves arriving within the shear-wave window display shear-wave splitting, and that the polarizations of leading shear-waves are consistently aligned in a NE/SW direction. The area is complicated and the tectonics are not well-understood, but the NE/SW direction is approximately perpendicular to the compressional axis in many of the fault-plane mechanisms of the earthquakes. These earthquakes are usually at depths between 5 and 12 km, although there are some deeper events nearby.
Parallel shear-wave polarizations, such as those observed, are expected to indicate the strike of nearly vertical parallel microcracks, which would be aligned parallel to the direction of maximum compression. Thus the shear-wave polarizations in the Peter the First Range indicate that the directions of principal stress are reversed in the rock above the earthquake foci where thrust faulting is taking place.     

山西霍山山前断裂晚第四纪活动特征和1303年洪洞8级地震

霍山山前断裂是山西临汾盆地北半部主边界断裂。本文根据沿断裂带的1:1万地质填图结果,详细地研究了霍山山前断裂的活动历史、断裂的分段性及其构造活动特征、不同时期以来的右旋错动幅度和滑动速率以及与1303年洪洞8级地震的关系。最后,根据山西地堑系内已获得滑动速率值的几条北北东向主干断裂的构造特殊性,讨论了地堑系两侧的一级右旋运动水平     

Pleistocene glacial relief of the central part of Mt. Prokletije (Albanian Alps)

The central and highest area of Mt. Prokletije (Albanian Alps) is situated in northern Albania and eastern Montenegro (at 42°30′N). The highest peak is Maja e Jezerces (2694 m). Detailed geomorphological mapping was used to reconstruct the positions of former glaciers. The longest Ropojana glacier had a length of 12.5 km and surface of 20 km²; others include Valbona Glacier (9.5 km, 10.5 km²), Grbaja Glacier (5 km, 6.7 km²) and Bogićevica Glacier (6 km, 6.9 km²). Three series of moraines can be distinguished: the lowest at an average altitude of 990 m (average ELA 1750 m), the middle series at 1350 m (ELA 1942 m), and the highest at 1900 m (ELA 2123 m). As no advanced dating methods have yet been used to provide a numerical chronological framework for these features, hypotheses are made based on the comparison with the advanced studies of other similar mountains in the Mediterranean region. The moraines of the first stage (lowest series) correspond to one of pre-LGM glaciations (Middle or even Early Würmian), the second stage moraines probably correspond to LGM, and the third stage could be attributed to Younger Dryas. The mapping included a number of inactive and active rock glaciers, as well as three small active glaciers (surface 5 ha and less), at 1980–2100 m altitude, in the area close to Maja e Jezerces.     

The structure of the Monte Amiata volcano-geothermal area (Northern Apennines, Italy): Neogene-Quaternary compression versus extension

The tectonic evolution of the Mt Amiata volcano-geothermal area is under discussion. Some authors state that this region, as well as the hinterland of the Northern Apennines, were affected by compression from the Cretaceous to the Quaternary. In contrast, most authors believe that extension drove the tectonic evolution of the Northern Apennines from the Early Miocene to the Quaternary. Field data, seismic analyses and borehole logs have been integrated in order to better define the structural features of the continental crust in the Mt Amiata geothermal area. In this paper I propose the hypothesis that the structure of the crust in the Mt Amiata volcano-geothermal area derives from two main geological processes: (1) contractional tectonics related to the stacking of the Northern Apennines (Cretaceous–Early Miocene), (2) subsequent extensional collapse of the hinterland of the mountain chain, and related opening of the Northern Tyrrhenian Sea (Early Miocene–Quaternary). Compressional and extensional structures characterise the Mt Amiata region, although extensional structures dominate its geological framework. In particular the extension produced: (a) Middle-Late Miocene boudinage of the previously stacked tectonic units; (b) Pliocene–Quaternary normal faulting which favoured the emplacement of a magmatic body in the middle-upper crust; and (c) the eruption of the Mt Amiata volcano, which gave rise to an acid and intermediate volcanic complex (0.3–0.19 Ma). The extension produced the space necessary to accommodate the Middle-Late Miocene marine and continental sediments. Pliocene and Quaternary normal and transtensional faults dissected the previous structures and influenced the Early Middle Pliocene marine sedimentation within the structural depressions neighbouring the Mt Amiata volcano. The magmatic body was emplaced at depth (about 6–7 km) during the Pliocene extension, and produced the eruption of the Mt Amiata volcano during the Late Pleistocene. This gave rise to local uplift, presently reaching about 3,000 m, as well as a negative Bouguer anomaly (−16 mgal), both centred on the Mt Amiata area. The crustal dome shows a good correspondence with the convex shape of the regional seismic marker known as the K-horizon, which corresponds to the 450°C isotherm, and the areas with greatest heat flow. This is probably a consequence of the above-cited magmatic body presently in the process of solidification. A Late Pleistocene eruption occurred along a crustal fissure striking N50° (Mt Amiata Fault), which crosscuts the crustal dome. Hydrothermal circulation, proven by the occurrence of thermal springs and gas vents (mainly CO₂ and H₂S), mainly occurs along the Mt Amiata Fault both in the northeastern ans southwestern sides of the volcano.     

Metamorphic fluid origins in the Osborne Fe oxide–Cu–Au deposit,Australia: evidence from noble gases and halogens

The Osborne iron oxide–copper–gold (IOCG) deposit is hosted by amphibolite facies metasedimentary rocks and associated with pegmatite sheets formed by anatexis during peak metamorphism. Eleven samples of ore-related hydrothermal quartz and two pegmatitic quartz–feldspar samples contain similarly complex fluid inclusion assemblages that include variably saline (<12–65 wt% salts) aqueous and liquid carbon dioxide varieties that are typical of IOCG mineralisation. The diverse fluid inclusion types present in each of these different samples have been investigated by neutron-activated noble gas analysis using a combination of semi-selective thermal and mechanical decrepitation techniques. Ore-related quartz contains aqueous and carbonic fluid inclusions that have similar ⁴⁰Ar/³⁶Ar values of between 300 and 2,200. The highest-salinity fluid inclusions (47–65 wt% salts) have calculated ³⁶Ar concentrations of approximately 1–5 ppb, which are more variable than air-saturated water (ASW = 1.3–2.7 ppb). These fluid inclusions have extremely variable Br/Cl values of between 3.8 × 10⁻³ and 0.3 × 10⁻³, and I/Cl values of between 27 × 10⁻⁶ and 2.4 × 10⁻⁶ (all ratios are molar). Fluid inclusions in the two pegmatite samples have similar ⁴⁰Ar/³⁶Ar values of ≤1,700 and an overlapping range of Br/Cl and I/Cl values. High-salinity fluid inclusions in the pegmatite samples have 2.5–21 ppb ³⁶Ar, that overlap the range determined for ore-related samples in only one case. The fluid inclusions in both sample groups have ⁸⁴Kr/³⁶Ar and ¹²⁹Xe/³⁶Ar ratios that are mainly in the range of air and air-saturated water and are similar to mid-crustal rocks and fluids from other settings. The uniformly low ⁴⁰Ar/³⁶Ar values (<2,200) and extremely variable Br/Cl and I/Cl values do not favour a singular or dominant fluid origin from basement- or mantle-derived magmatic fluids related to A-type magmatism. Instead, the data are compatible with the involvement of metamorphic fluids that have interacted with anatectic melts to variable extents. The ‘metamorphic’ fluids probably represent a mixture of (1) inherited sedimentary pore fluids and (2) locally derived metamorphic volatilisation products. The lowest Br/Cl and I/Cl values and the ultra-high salinities are most easily explained by the dissolution of evaporites. The data demonstrate that externally derived magmatic fluids are not a ubiquitous component of IOCG ore-forming systems, but are compatible with models in which IOCG mineralisation is localised at sites of mixing between fluids of different origin. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Using cryptotephras to extend regional tephrochronologies: An example from southeast Alaska and implications for hazard assessment

Cryptotephrochronology, the use of hidden, diminutive volcanic ash layers to date sediments, has rarely been applied outside western Europe but has the potential to improve the tephrochronology of other regions of the world. Here we present the first comprehensive cryptotephra study in Alaska. Cores were extracted from five peatland sites, with cryptotephras located by ashing and microscopy and their glass geochemistry examined using electron probe microanalysis. Glass geochemical data from nine tephras were compared between sites and with data from previous Alaskan tephra studies. One tephra present in all the cores is believed to represent a previously unidentified eruption of Mt. Churchill and is named here as the ‘Lena tephra’. A mid-Holocene tephra in one site is very similar to Aniakchak tephra and most likely represents a previously unidentified Aniakchak eruption, ca. 5300-5030 cal yr BP. Other tephras are from the late Holocene White River eruption, a mid-Holocene Mt. Churchill eruption, and possibly eruptions of Redoubt and Augustine volcanoes. These results show the potential of cryptotephras to expand the geographic limits of tephrochronology and demonstrate that Mt. Churchill has been more active in the Holocene than previously appreciated. This finding may necessitate reassessment of volcanic hazards in the region.