贵州西南部贞丰背斜金(锑)成矿分析与预测

本文以近期贞丰背斜构造带金(锑)矿勘查成果,结合区域地质特征与规律,对贞丰背斜构造带成矿地质环境和控矿地质条件进一步作出全面分析,指出了有利金(锑)矿赋存地段,提出找矿远景区,对后续地质矿产勘查具有较强的指导意义。     

Crack Coalescence in Molded Gypsum and Carrara Marble: Part 2—Microscopic Observations and Interpretation

Experimental uniaxial compression loading tests were conducted on molded gypsum and Carrara marble prismatic specimens to study the cracking and coalescence processes between pre-existing artificial flaws. The study showed that material had an influence on the cracking and coalescence processes (see the companion paper in this issue). As reported in the companion paper, one of the pronounced features as observed in the high-speed video recordings was the development of macroscopic white patches prior to the development of observable cracks in marble, but not in gypsum. This paper (part 2) deals with the microscopic aspects of the study. Specifically, the scanning electron microscope (SEM) and the environmental scanning electron microscope (ESEM) imaging techniques were used to study the microscopic development of white patches and their evolution into macroscopic tensile cracks and shear cracks in marble, and the microscopic initiation of hair-line tensile cracks and their evolution into macroscopic tensile cracks in gypsum. The microscopic imaging study in marble showed that the white patches were associated with extensive microcracking zones (process zones), while the extent of process zone development in gypsum was limited. The comparison of the macroscopic and microscopic results indicates that the different extent of microcracking zone development, related to the material textural properties, is a key factor leading to different macroscopic cracking behavior in gypsum and marble.

Oligocene biogeography of the North Pacific (Implications of Mollusks)

First biogeographic maps are proposed for the late Eocene-Oligocene of the North Pacific. The maps are compiled based on distribution of 120 molluscan species studied in 30 reference sections of the region. The analyzed Machigar (Sakhalin), Rategin, Amanina-Gakh (western Kamchatka), Asagai-Momidziyama (Japan) type assemblages and their age analogues are well known and described long ago. Over 50 schematic biogeographic maps illustrate distribution areas of different taxa in the late Eocene, early Oligocene, and late Oligocene epochs. Some of them characterize distribution areas of individual species, while the others depict habitat areas of typical (Machigar and Rategin) assemblages or certain genera different in terms of their thermotropism. Analysis of the maps resulted in recognition of the Japan-Kamchatka and Kamchatka-North American paleoprovinces, and indications of general gradual seawater temperature decrease during the Oligocene are defined. The attention is paid to the commenced diversification of North Pacific biota that leads to formation of boreal communities and also to different-rank the amphipacific dusjunctions.     

An X-ray excited optical luminescence study of a zoned quartz crystal from an emerald-bearing quartz vein,Hiddenite, North Carolina,USA

The optical luminescence excited with synchrotron radiation along a preferential orientation of a quartz crystal has been investigated. It is found that the crystal is composed of two distinct regions, only one of which luminesces upon X-ray excitation. This luminescence is generally uniform and exhibits emission bands in the blue (470 nm with a shoulder at 522 nm) and in the UV (340 nm) regions of the spectrum. The branching ratio for the intensity of these bands is sensitive to the excitation energy across the Si K-edge. XANES spectra collected by partial luminescence yield (PLY) suggest that both emission bands originate from the de-excitation of Si atoms in the quartz. The possible defect sites within the crystal structure that could account for the observed luminescence are investigated and discussed. Additional experiments are proposed to verify this assignment of the optical emission bands.     

Early burial mud diapirism and its impact on stratigraphic architecture in the Carboniferous of the Shannon Basin,County Clare,Ireland

Delta fronts are often characterized by high rates of sediment supply that result in unstable slopes and a wide variety of soft‐sediment deformation, including the formation of overpressured and mobile muds that may flow plastically during early burial, potentially forming mud diapirs. The coastal cliffs of County Clare, western Ireland, expose Pennsylvanian (Namurian) delta‐front deposits of the Shannon Basin at large scale and in three dimensions. These deposits include decametre‐scale, internally chaotic mudstone masses that clearly impact the surrounding sedimentary strata. Evidence indicates that these were true mud (unlithified sediment) diapirs that pierced overlying strata. This study documents a well‐exposed ca 20 m tall mud diapir and its impact on the surrounding mouth‐bar deposits of the Tullig Cyclothem. A synsedimentary fault and associated rollover dome, evident from stratal thicknesses and the dip of the beds, define one edge of the diapir. These features are interpreted as recording the reactive rise of the mud diapir in response to extensional faulting along its margin. Above the diapir, heterolithic sandstones and siltstones contain evidence for the creation of localized accommodation, suggesting synsedimentary filling, tilting and erosion of a shallow sag basin accommodated by the progressive collapse of the diapir. Two other diapirs are investigated using three‐dimensional models built from ‘structure from motion’ drone imagery. Both diapirs are interpreted to have grown predominantly through passive rise (downbuilding). Stratal relationships for all three diapirs indicate that they were uncompacted and fluid‐rich mud beds that became mobilized through soft‐sediment deformation during early burial (i.e. <50 m, likely <10 m depth). Each diapir locally controlled the stratigraphic architecture in the shallow subsurface and potentially influenced local palaeocurrents on the delta. The mud diapirs studied herein are distinct from deeper ‘shale diapirs’ that have been inferred from seismic sections worldwide, now largely disputed.     

Subduction,fluids, and accessory minerals: a celebration of the career of Sorena S. Sorensen

ABSTRACT

This is a preface to the topical issue entitled ‘Subduction, Fluids, and Accessory Minerals: A Celebration of the Career of Sorena S. Sorensen’     

用共偏移距反射法拓展地质剖面的解释深度

针对核电工程选址中的能动断层地质调查工作需要,提出了利用共偏移距浅层地震反射时间剖面来拓展地质剖面解释深度的技术方法,通过物性和岩性的综合解释来提高对能动断层鉴别及其产状确定的可靠性.探测试验结果表明该方法是有效可行的.地质剖面上描述的断裂破碎带在共偏移距时间剖面上反应明显,二者可以相互印证,优势互补.该技术方法可用于类似工程地质调查和第四系覆盖较薄地区的隐伏断层探测.     

基于地震带细致划分为地震构造区的概率地震危险性分析

在我国当前地震安全性评价中,普遍使用考虑地震活动时空不均匀性的概率地震危险性分析方法(CP-SHA),它规定以地震带为统计区域计算地震活动性参数b值和v4值。正在编制的中国地震动区划图(五代图)提出了针对潜在震源区进行三级划分原则:划分地震带、地震带上划分地震构造区、地震构造区内再划分潜在震源区。本文提出以地震构造区为统计区域回归统计方法计算b值和v4值,然后进行概率危险性分析计算,这样得到的结果可能更为合理。     

Formation mechanism of carbonate cemented zones adjacent to the top overpressured surface in the central Junggar Basin,NW China

Carbonate cemented zones are normally adjacent to the top overpressured surface in the central Junggar Basin,NW China.Stable carbon and oxygen isotopic compositions and petrological investigations of carbonate cements in the carbonate cemented zones indicate that:(1) carbonate cements are composed dominantly of ferrocalcite,ferroan dolomite,and ankerite;(2) carbonate cements are formed under a high temperature circumstance in the subsurface,and organic fluid migration has an important effect on the formatio...     

Significance of nearshore wave parameters in identifying vulnerable zones during storm and normal conditions along Visakhapatnam coast,India

The nearshore parameters, viz., wave runup, wave setup, and wave energy have been estimated during storm and normal conditions of SW monsoon (June–September) and NE monsoon (November–February) by empirical parameterization along Visakhapatnam coast. These results were compared with the field observations during three storms of SW monsoon season in the year 2007. The higher nearshore wave energies were observed at R.K. Beach, Jodugullapalem beach, and Sagarnagar beach during both the seasons. During storm events, the higher wave energies associated with higher wave runups cause severe erosion along the wave convergence zones. The storm wave runups (SWRUs) were higher at R.K. Beach, Palm beach, Jodugullapalem beach, and Sagarnagar Beach. The yearly low wave energy was observed at Lawson’s Bay with lowest wave runup, considered as safest zone. R.K. Beach, Palm beach, and Jodugullapalem beach are identified as vulnerable zones of wave attack. It is noteworthy that in addition to wave energies, wave runups and wave setups also play a vital role in endangering the coast.