米仓山地区金矿特征及找矿远景分析

米仓山地区的金矿主要产在太古代—早元古代后河岩群绿岩和澄江期陆壳重熔S型花岗岩中,金矿化主要受SN、NE向的韧脆性剪切带所控制,发育多期次、多阶段的热液蚀变活动,成矿物质主要来源于澄江期重熔花岗岩浆期后含金热液,还包括部分变质热液。米仓山地区金矿的找矿前景广阔。     

Fishers' perceptions,facilitating factors and challenges of community-based no-take zones in the Sian Ka’an Biosphere Reserve,Quintana Roo,Mexico

In response to fisheries decline in the Mexican Caribbean and continuing deterioration of the Mesoamerican Reef, conservation NGOs have begun to negotiate and collaboratively design a network of no-take zones (NTZs) with three fishing cooperatives in the Sian Ka’an Biosphere Reserve (SKBR), among other places along the coast of Quintana Roo. Spiny lobster (Panulirus argus) is the target of the main fishery within cooperative concessions. Fishers are uniquely positioned to enforce and monitor NTZs and evaluate their effectiveness. This study analyzes fishers' perceptions as indicators of social acceptance of NTZs, and identifies facilitating factors and challenges of the community-based process. Consistent with similar studies, responses of fishers (89 out of a population of 124) to a semi-structured interview showed that perceptions of NTZs largely reflect fishers' concerns and interests. A high proportion of fishers accurately identified main NTZ objectives of regulation, conservation and economic improvement, as well as NTZ locations. Further, fishers cared about ecosystem sustainability and, because NTZs would not significantly limit their main economic activity, endorsed the initiative while expecting additional benefits. Declining trends in lobster catch influenced a perceived need for NTZs. Major concerns were that illegal fishers would reap NTZ benefits and that economic impacts and benefits were uncertain. Most fishers found the decision-making process inclusive, were willing to take responsibility for enforcing NTZs and believed people leading the process were trustworthy. Differences in endorsement of NTZs among cooperatives points to the importance of understanding fishers’ incentives to collaborate, and the leadership and organizational dynamics which shape participatory processes. This analysis highlights challenges in advancing NTZs in complex ecological, socio-economic and regulatory contexts. It underscores the need for community-based processes that transcend understanding of conservation measures but also invests in sustainable, operative and trustful working relationships, as well as the urgency of interdisciplinary approaches in ensuring effective design and implementation of this relatively new fishery management tool.     

从地壳上地幔构造看大陆碰撞带岩石圈的克拉通化

本篇讨论超级大陆汇聚后逐渐变为克拉通或扩大克拉通的作用过程,即指经及大陆碰撞地体汇聚后新形成的大陆块逐渐转变为刚性克拉通的作用过程。增生大陆岩石圈的克拉通化的作用后果,包括大陆地壳密度的增加,岩石圈地幔的增厚和大地热流值的下降,使大陆岩石圈逐渐刚性强化。大陆碰撞后形成的大陆块必须经过克拉通化的过程,才能逐渐成为刚性克拉通。作用过程主要包括:①上地壳沉积碎屑岩石结晶岩化和中地壳岩石角闪岩化;②下地壳岩石基性化;③大陆碰撞带下凹莫霍面的磨平;④岩石圈地幔底侵加厚形成陆根。从大陆碰撞带转变为克拉通的过程也是岩石圈地幔不断增厚而地壳缓慢变硬变冷的过程。这个过程包含以下作用:区域变质作用,交代作用和岩石圈幔源岩浆的底侵。这个过程时间尺度比碰撞造山作用大一个级次。长期的底侵作用使地壳岩石密度和强度不断加大,改变岩层的矿物成分和局部结构。当大陆岩石圈克拉通化到一定程度之后,由于下方软流圈的热能供应逐渐减缓,使岩石圈地温梯度缓慢下降,最终结果会形成大陆根。由于显生宙大陆碰撞带岩石圈强度弱,大陆碰撞时更容易造成岩石圈变形,因此大陆碰撞的板内效应主要发生在大陆内的显生宙碰撞带。显生宙大陆碰撞带如果再次受到大陆碰撞板内效应的作用,其克拉通化的过程必然会推迟。     

Mica Inclusions inside Host Mica Grains from the Sutlej Section of the Higher Himalayan Crystallines, India—Morphology and Constrains in Genesis

Abstract: Biotite and muscovite inclusions inside mica host minerals from the Sutlej section of the Higher Himalayan Crystalline were studied under an optical microscope. These inclusions formed possibly by local recrystallization of mica grains during regional prograde metamorphism, with some affected by top-to-SW shear leading to parallelogram shapes. Recrystallization may have been assisted by solution transfer along the cleavage planes of the host grains. The relative competency of deformed phyllosilicate inclusions with the same or different composition to the host depends on the size and orientation of (001) cleavage planes of the inclusions relative to the host. Shearing of mica inclusions led to their parallelogram geometries within the contained mica inclusions. Some of the sheared inclusions deflect cleavage planes in the host minerals and define flanking microstructures. Trapezoid-shaped inclusions are a new finding that deserves more attention for their genesis. These structurally anisotropic inclusions did not originate from sub-grains, secondary infillings or retrogression. These inclusions are also not related to pseudomorphism, isomorphism, folding of the bulk rock etc. Some of the inclusions formed by recrystallization of the host mineral during top-to-SW ductile shear.     

青海省都兰县阿拉克湖地区水系沉积物地球化学特征及找矿方向

分析了区内的水系沉积物地球化学参数特征及其元素的相关性,认为元素(地球化学)异常(高值区)严格受东昆中断裂带、东昆南断裂带、布青山南坡乌断裂带,以及阿尼玛卿蛇绿岩带和东昆中蛇绿岩带,古-中元古代地层、岩体接触带、热液活动、脉岩等因素联合控制。根据异常特征与成矿地质条件,圈定了找矿远景区5个,且为该区下一步的找矿工作指明了方向。     

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Groundwater dating with 3H and SF6 in relation to mixing patterns,transport modelling and hydrochemistry

A comprehensive study of a sandy aquifer of deltaic origin in southern Poland included water chemistry, isotopes, dissolved trace gases and transport modelling. Tritium, sulphur hexafluoride (SF₆) and freons (F‐11, F‐12 and F‐113) showed the presence of modern waters in the recharge areas and shallow confined parts of the aquifer. The presence of older Holocene waters farther from the recharge areas was indicated by lack of ³H, SF₆ contents ≤0·02 fmol l⁻¹ and relatively low ¹⁴C values. The discharge from the system is by upward seepage in the valley of a major river. Pre‐Holocene waters of a cooler climate, identified on the basis of δ¹⁸O, δ²H, ¹⁴C, Ne and Ar data, were found in some distant wells. Concentrations of N₂, Ne and Ar determined by gas chromatography were used for calculating the noble gas temperatures, air excess needed for correction of SF₆, and nitrogen content released by denitrification process. The time series of ³H content available for some wells supplied quantitative information on age distributions and the total mean ages of flow through the unsaturated and saturated zones. The derived ³H age distributions turned out to be very wide, with mean values in the range of about 30 to 160 years. For each well with determined ³H age, the SF₆ data showed either a lower age range or the possibility of a lower age as expected due to shorter travel times of SF₆ through the unsaturated zone, which most probably also resulted in different types of age distributions of these tracers. Freons appeared to be of little use for individual age determinations. A quantitative estimation of two‐component mixing from SF₆ ³H relations is not possible unless the travel time of ³H through the unsaturated zone is comparable to that of SF₆. The ratio of integrals of the response function over the age range with tracer and the whole response function yields the ratio of water with tracer to total flow of water. That ratio is a tracer‐dependent function of time. Transport modelling of SF₆ tracer done with MT3D code yielded initially large discrepancies between calculated and measured tracer concentrations. Some discrepancies remained even after calibration of the transport model with SF₆. Simulation of tritium contents with a calibrated transport model yielded reasonable agreement with measured contents in some wells and indicated a need for further investigations, particularly in the eastern part of the aquifer. The existence of distinct hydrochemical zones is consistent with the tracer data; young waters with measurable ³H and SF₆ contents are aerobic and of HCO₃ Ca or HCO₃ SO₄ Ca types. Slightly elevated Na and Cl contents, as well as the highest concentrations of SO₄ and NO₃ within this zone are due to anthropogenic influences. Anaerobic conditions prevail in the far field, under the confining cover, where pre‐bomb era Holocene waters dominate. In that zone, dissolved oxygen, NO₃ and U contents are reduced, and Fe, Mn and NH₄ contents increase. In the third zone, early Holocene and glacial waters occur. They are of HCO₃ Ca Na or HCO₃ Na types, with TDS values higher than 1 g l⁻¹ and Na content higher than 200 mg l⁻¹, due to either small admixtures of ascending or diffusing older water or freshening of marine sediments, a process that is probably occurring till the present time. Copyright © 2005 John Wiley & Sons, Ltd.     

Petrology, geochronology, and tectonics of shear zones in the Zermatt–Saas and Combin zones of the Western Alps

Metre to tens‐of‐metre wide, steeply dipping, greenschist facies shear zones that cut blueschists and eclogites of the Combin and Zermatt–Saas Zones at Täschalp and in adjacent areas of the western Alps were sites of extensive recrystallization driven by fluid flow and deformation. Rb–Sr data imply that these shear zones formed at 42–37 Ma with a systematic younging of structures northward toward, and into, the hangingwall of the Mischabel Structure. Shearing commenced at 400–475 °C and 400–500 MPa and continued as pressures and temperatures fell to 300–350 °C and 300–350 MPa. Individual shear zones were active for 2–3 Myr with later lower grade stages of shearing concentrated into narrow zones. Fluids that infiltrated the shear zones were water rich (X_H2O > 0.9). Alteration zones around albite veins and at the margins of serpentinite bodies are penecontemporaneous with these shear zones and formed at approximately the same conditions. The eclogites were exhumed from c. 64 km at 44 Ma to 14–16 km at 42–41 Ma implying exhumation rates of 2–5 cm yr^?1. Rapid exhumation was probably achieved by extension aided by buoyancy, following subduction of continental crust, and rapid erosion. The shear zones form part of a regional‐scale extensional system responsible for a significant portion of the exhumation of the subducted oceanic crust.     

辽宁省大石桥－吉洞峪一带辽河岩群变质地层的对比研究

辽宁省大石桥－吉洞峪一带出露的主要为古元古代的变质层状岩系，由云母片岩、长英质粒岩和大理类组成。区域上形成一大型北东向的复式向斜构造。复向斜南北两翼变质地层对比问题是辽吉东部辽河岩群研究的主要内容之一。作者根据五年来在大石桥－吉洞峪一带进行１∶５万区调所获得的新资料，从标志层及组合标志层、岩相学特征、主要标志层的岩石化学和稀土地球化学特征、变质作用演化等方面的研究入手，讨论了复向斜两翼变质地层对比的问题。结果表明，辽河岩群构成复向斜南北两翼的变质地层是完全可以对比的，从而进一步证实辽河岩群是一个不可分割的整体     

灞源韧性剪切带特征及其地质意义

本文对灞源地区不同时代的韧性剪切带的运动学、动力学特征进行了研究。笔者认为,前人所称的部分太华群(Arth_3b)是太古宙末期太华群韧性变形的产物;张家坪花岗岩以左旋螺旋式上升侵位;燕山期,多期活动韧性剪切带是本区金矿形成富集的主要原因之一。