A tectonic origin of magnetic fabric in the Shemshak Group from Alborz Mts. (northern Iran)

The magnetic lineation observed in “undeformed” sedimentary units has been interpreted either as an indication of paleoflow direction, or as a result of tectonic overprint which progressively modifies the original sedimentary fabric related to compactional processes. Distinguishing between the two processes is not always easy. In fact, most studies of the Anistropy of Magnetic Susceptibility (AMS) of “undeformed” sequences have been carried out in fine-grained sediments from foredeep sequences, which are characterized by sedimentary flow directions which are almost parallel to the main deformation structures, like thrust faults and folds. In the Alborz Mts., the Upper Triassic–Lower Jurassic Shemshak Group was deposited in a foreland to molassic basin of the Eo-Cimmerian orogen and now outcrops in several folds which are oriented parallel to the curved chain. Paleoflow directions are generally oblique to the main tectonic structures, being directed SSW to SSE and showing negligible changes in their orientation along the Alborz Mountains. We have, therefore, the opportunity to distinguish between tectonic- or sedimentary-related origins of the magnetic lineation. The AMS results show that magnetic lineations of the Shemshak Group are oriented almost parallel to the main fold axes and thrust structures, which follow the Alborz Mts. curved trend, suggesting that magnetic lineation is of tectonic origin in fine to medium grained, mostly massive sandstones, and confirming that AMS is a valuable tool to study deformation processes in sedimentary rocks.     

地球的挥发分循环与宜居环境演变SCIEI北大核心CSCD

地球宜居环境的形成和演变与挥发分循环密切相关。宜居性受地球表层系统中挥发分组成和变化的直接影响,但其本质上受控于地球深部系统的挥发分释放和循环过程。本文简要介绍了地球挥发分的起源、大气圈和海洋的形成与演化、深部挥发分释放及对气候环境的影响、俯冲带挥发分循环等几个方面的研究概况。期望本文能使读者更好的理解本专辑稿件的内容,激发起同行对挥发分研究的兴趣,促进我国挥发分相关研究的发展。     

长白山火山灾害研究概观

本文概述了当代火山灾害与长白山火山研究的现状,简要地介绍了在火山灾害研究中取得的资料、认识与进展,可供进一步研究参考。     

遥感技术在喀喇昆仑区域地层对比中的应用

喀喇昆仑地区康西瓦断裂以南被划为晚三叠世的变质杂岩,由两套影像特征迥然不同的岩石组成,其中一套与塔里木板块的结晶基底非常相似,野外实勘证实这是一套深变质岩,其岩性组合及变形变质特征与塔里木板块的元古界一致;另一套为晚三叠世地层。两套地层间为一条在遥感图像上具有明显的线性特征但还未曾识别的大型断裂,根据对两侧地质环境的分析,认为它可能是一条重要的地质界线。     

Petrographic study of the Miocene Mizunami Group,Central Japan: Detection of unrecognized volcanic activity in the Setouchi Province

A petrographic study of sandstones from the Miocene Mizunami Group in Central Japan has been performed on core samples from a single borehole, in order to evaluate the provenance of the sedimentary rock. Evaluation of the provenance is based on bulk mineral, heavy mineral and plagioclase contents and on whole rock chemical compositions. The sandstones studied are divisible into three types; the first type is characterized by the occurrence of biotite and plagioclase ranging from albite to oligoclase, the second type is characterized by the dominance of amphibole and labradorite with pyroxene (clinopyroxene > orthopyroxene), and the third type is characterized by the dominance of pyroxene (orthopyroxene > clinopyroxene) and andesine with lesser labradorite, bytownite and anorthite. The first type is interpreted to be derived from the basement granite, whereas the others were derived mostly from volcanic ash, judging from their mineral compositions. The volcanic activity that supplied the volcanic ash to the Mizunami Basin occurred in two phases, distinguishable by variations in their mineralogical and geochemical compositions, an indication of change in character of the volcanic activity. This petrographic study of the sandstones in the Mizunami Group suggests that unrecognized volcanic activity occurred around the Mizunami Basin, even though potential provenance of the volcanic ash has not yet been identified.     

The Effects of Different Substrates on Ammonium Removal in Constructed Wetlands: A Comparison of Their Physicochemical Characteristics and Ammonium‐Oxidizing Prokaryotic Communities

A vertical flow constructed wetland (VFCW) filled with natural zeolite had higher ammonium removal (82.4–94.0%) than another VFCW filled with volcanic rock (51.3–69.4%) treating piggery wastewater under any of three recirculation ratios. To reveal the underling reasons, physicochemical characteristics and ammonium‐oxidizing prokaryotes (AOPs) of two substrates were determined. The calculated maximum ammonium adsorption of zeolite (11.6 mg g^?1) was remarkably higher than that of volcanic rock (0.21 mg g^?1), mainly because the former contains two cationic binding crystalline species, and montmorillonite. Quantitative analyses indicated that ammonium‐oxidizing archaea (AOA) are the dominant AOP of zeolite and ammonium‐oxidizing bacteria (AOB) are the dominant AOP of volcanic rock respectively. Diversity and phylogenetic analysis further showed that both AOB and AOA communities were significantly different between two substrates. Nitrosospira‐like AOB (92.6%) and sediment/soil clade AOA (71.4%) were the main components of AOB and AOA in natural zeolite, whereas Nitrosomonas‐like AOB (76.1%) and water/sediment clade AOA (77.1%) dominated the AOB and AOA in volcanic rock. These results suggest that the substrates show high selectivity to AOP community. Thus, in addition to physicochemical characteristics, the AOP of substrates is very likely to affect ammonium removal in VFCWs.     

小秦岭变质岩系层序划分新方案

第二轮１∶５万区调采用岩石─构造─地质事件法填图，重新研究了小秦岭地区结晶基底变质岩系的层序（时序）关系，指出该岩系应予解体，提出了新的划分方案。该方案将这套岩系两分（上基底、下基底），其间为异岩不整合界面。下基底以变质侵入岩为主体，按时序从早到晚为基性喷发表壳岩、杨砦峪灰色片麻岩、四范沟片麻状花岗岩，时代属晚太古代；上基底为一套副变质岩，自下而上为：观音堂组、焕池峪组，时代属早元古代。     

庐山筲箕洼组与星子岩群年代地层关系及SHRIMP锆石U-Pb年龄的制约

本文报道在庐山筲箕洼组中获得细碧岩SHIRMP锆石U-Pb年龄(840±6) Ma,MSWD=1.3,流纹岩锆石U-Pb年龄(833±4) Ma,MSWD=1.4,和流纹岩锆石U-Pb年龄(831±3) Ma,对应的MSWD=1.47.而在星子群流纹岩中获得206pb/238U年龄为(825±5)Ma,对应的MSWD=0.46.笔者依据上述精确锆石年龄,首次提出将筲箕洼组明确定位于星子岩群之下.本文结合“江南造山带”锆石U-Pb年龄:东部变质基底的双桥山群,西部变质基底梵净山群和似盖层下江群以及中部变质基底冷家溪群和似盖层板溪群的锆石SHRIMP U-Pb年龄,将筲箕洼组定位于“武陵运动”之下的新元古代地层.依据星子岩群年龄数据,首次将星子岩群明确定位于筲箕洼组之上与双桥山群为同期的深变质岩.该年龄对限定区域地层对比和构造演化都有着重要意义.上述锆石U-Pb年龄标示了赣西北地区同样存在820 Ma界面上下的新元古代地层,为江南古陆变质地层的对比提供了新的年代学数据.     

北淮阳浅变质岩带卢镇关群变质压力及其对大别造山带演化的指示

卢镇关群是北淮阳浅变质岩带的重要组成部分,其俯冲历史对于证明超高压岩石经历了深俯冲及获得完整的大别造山带演化历史具有重要意义.本次工作在霍山牛角冲、与儿街卢镇关群岩石中采集了含石榴子石的黑云二长片麻岩和石榴黑云片麻岩进行电子探针分析,并通过石榴子石—黑云母—斜长石—石英压力计计算获得了卢镇关群的变质压力变化于1.89～1.99 GPa,其平均值为1.94 GPa.根据造山带内中—上地壳岩石的平均密度,获得了卢镇关群曾俯冲于地下64.7 km的深度.这表明位于大别造山带最北缘的北淮阳带曾俯冲于较大深度,支持前人关于华南、华北板块缝合线位于北淮阳带以北的结论.     

平邑盆地官庄群湖相碳酸盐岩的古地理意义

[摘 要] 本文旨在以平邑盆地官庄群湖相碳酸盐岩为例,研究湖相碳酸盐岩的古地理指示意义。以沉积学理论为指导,依据野外露头剖面分析了平邑盆地古近纪官庄群的地层及其沉积特点,结合盆地的形成及演化,分析了古生物、古气候、物源、水介质物理化学条件等沉积环境条件,明确了官庄群湖相碳酸盐岩沉积时的古地理格局与特征。研究表明平邑盆地在古近纪官庄群沉积时为温暖的内陆淡水湖泊环境,构造活动相对静止,地形平坦,有利于湖泊相碳酸盐岩沉积,且碳酸盐岩集中发育在浅水、中等偏低能量、低陆源碎屑物质的环境。从而说明湖相碳酸盐岩地层形成的古地理背景为构造活动平静、地形平坦、浅水低能沉积环境。