剪切带型金矿中金沉淀的力化学过程与成矿机理探讨

剪切带型金矿是一种重要的金矿床类型,有关该类型金矿的成因问题已开展了大量研究,但对于剪切带中金的沉淀析出机制和成矿过程仍存在较大争议,对于赋矿部位的构造属性与矿床关系的研究尚显薄弱。对此笔者整理分析了近年来国内外有关剪切带型金矿的研究进展,并结合我国胶东金矿的研究实例,运用断层阀和力化学理论分析发现,无论是脆性还是韧性剪切带,无论是脉型还是蚀变岩型金矿,其成矿的关键部位均与构造应力集中而导致的脆性破裂(特别是R、T、R’破裂的产生)和碎裂作用以及(多期)岩体侵位密切相关,并且脆性破裂所导致的压力骤降从而引发流体闪蒸的力化学过程可能是造成金沉淀析出成矿的有效机制,其中多期岩体侵位所提供的流体是成矿的物质基础。此外,从国内外实例可以看出,剪切带中的脆性破裂不仅发生于脆性或脆韧性构造域,也可以发生在较深层次的韧性构造域中,尽管韧性域中产生脆性破裂的原因还不十分清楚,但这可能是韧性剪切带成矿的关键机制之一。最后,综合岩体、流体、剪切带三者对成矿的耦合作用,文中提出剪切带型金矿的成矿机理为:(多期)岩体侵位-热液活动-构造剪切-应力集中-脆性破裂(碎裂)产生-压力骤降-流体闪蒸-元素(金)析出,如此循环往复方可形成大型剪切带型金矿。     

Re‐establishment of soil water repellency after destruction by intense burning in a Mediterranean heathland (SW Spain)

Soil water repellency has been conventionally considered as a fire‐induced effect, but an increasing number of studies have suggested that natural background repellency occurs in many soil types, and many of them have suggested that water repellency can be re‐established over time after being destroyed. An experimental fire was conducted to study changes of the soil surface during the first 18 months following intense burning. The main objectives of this paper are as follows: (1) to investigate in situ water repellency changes at three soil depths (0, 2 and 4 cm) immediately after burning; (2) to evaluate the medium‐term evolution of water repellency under field conditions; and (3) to outline the main hydrological consequences of these changes. Also, different water repellency tests (water drop penetration time, ethanol percentage test (EPT) and contact angle (CA) between water drops and the soil surface) were carried out for comparison purposes. Field experiments showed that soil water repellency was partly destroyed after intense burning. Changes were relatively strong at the soil surface, but diminished progressively with depth. Levels of water repellency were practically re‐established 18 months after burning. This suggests that water repellency in the studied area is not necessarily a consequence of fire, but can instead be a natural attribute. Finally, although limited in time, destruction of soil water repellency has important consequences for runoff flow generation and soil loss rates, and, indirectly, for water quality. Copyright © 2009 John Wiley & Sons, Ltd.     

渤海陆缘地震的力学特征和成因

渤海陆缘是华北强震活动区,如1966年的邢台震群,1967年的河间地震,1969年的渤海地震,1975年的海城地震,1976年的唐山震群和1983年的菏泽地震,都是在该区发生的。显然,深入研究该地区的构造运动和地震成因是有重要科学意义的。本文拟从应力场角度进行研究。     

临汾裂谷现代构造应力场特征及其数值模拟

根据断层错动资料和小地震的平均震源机制解结果,运用弹性力学的叠加原理,对临汾裂谷作三维有限元模拟,反演其构造应力场。结果表明,临汾裂谷现今主要受南东东-北西西向引张力作用,辅之以北东-南西方向的挤压,同时在裂谷的中心叠加有底层拖曳的深部作用。     

Influence of “stress reversal” on rock resistivity during loading procedure

The properties of rock resitivity were studied under pressure, particularly with “stress reversal”, a procedure in which the pressure applied was increased and decreased. It was observed that, 1) With pressure increasing, the main feature of resistivity change was increase-steady-decrease for high-saturation rock samples (saturation 70–100%). But the main feature for low-saturation samples was different. 2) In 10 out of 11 cases of “stress reversal” for high-saturation samples the resistivity droped (about 2%). Such drop could explain the anomalies in geoelectricity terms, which are commonly observed before earthquakes in China. 3) It was also observed shortly before rock failure that, a) the resistivity drops more dramatically (about 20%) during “stress reversal” period, which is much more than ordinary drops. b) these drops occurred not only during stress decrease but also during stress increase. c) Resistivity exhibits anisotropy: the resistivity along different directions may differ by 10%. These three features may indicate that the rock is nearing failure, while ordinary resistivity drops are only connected with “stress reversal” and may not mean the imminence of rock failure. 4) Resistivity increase was observed during the “stress reversal” period for low-saturation rock samples. The results mentioned above were explained with the effect of water flowing in and out of the cracks of rock. The temporary factors which yield a reduction of the maximum main stress, may enhence the possibility of earthquake occurrence.     

帕米尔-兴都库什地区地震空间分布特征及应力场特征

本文研究了兴都库什及帕米尔地区地震的空间分布.发现h<70km的地震分布广泛,h≥100km的地震形成-S形的倾斜中源地震带.在71.5°E以西,中源地震带倾向接近正北,倾角随深度变化,在深部接近垂直,且倾角自西向东逐渐变陡,在71.5°E以东,倾向逐渐由东南变为正南. 分析了121个m_b≥5.0地震的机制解.浅源地震机制解的P轴大多位于NS和NNW-SSE方向,且多近水平,反映此区受到NS或NNW-SSE方向挤压.各剖面应力轴分布规律性强,在150km以下,总的趋势是机制解的T轴接近于倾斜的中源地震带的下倾方向,而P轴倾角较小且垂直于倾斜的中源地震带的走向.     

云南耿马7.2级地震地表破裂带研究

根据野外考察的实际资料,本文介绍了耿马7.2级地震地表破裂带的展布,结构要素及组合、位移分布等情况。同时依据位错资料对破裂带的应力活动及断裂两盘的运动状态进行了初步分析。认为本次地震发震构造以右旋走滑为主兼具张性,主压应力优势方位为N5°—10°E。断层两盘相对运动的总体方向为N55°W左右,断层运动的滑移角在30°—40°之间     

注水诱发地震的震源应力场和尾波衰减特征

利用区域性台网记录测定了任邱油田注水诱发地震的震源应力场和尾波衰减特征,结果表明地壳上层有很大水平应力,断层面解受注水井附近局部原生断层影响与华北现代应力场的优势破裂方向和错动方式有差别。地震应力降分布范围为0.2—3.0巴。平均尾波Q_0值为75,属于地壳上部沉积岩层的正常情况,发现在时间上表现出与注水量增减有关的波动。在空间上表现出震群密集区Q_0值较外围区偏低的特点     

澜沧—耿马地震震源动力学参数研究

本文使用沧澜—耿马地震主震后在震区建立的数字地震仪记录,用波谱法测算澜沧—耿马余震的震源动力学参数。就这些参数的统计特征,对该双主震型两主震区的地下介质不同状态予以讨论。     

长江中下游地震同青藏高原北部地震的相关性

本文对比了1910—1987年发生的长江中下游地震和青藏高原北部地震,发现两者有比较好的对应关系。一般是,青藏高原北部先发生M≥6级地震,而后长江中下游地区发生M≥19/4级地震。对1910年以来的21次地震进行了统计分析,得到复相关系数R=0.74,能够在很高的显著性水平上通过F检验。地震活动在时间、空间、强度上的相关,现代构造运动及应力场等事实表明,长江中下游地震活动可能主要受青藏高原向东的横向推移运动的影响。