北祁连西段祁青构造混杂岩中的单颗粒锆石U-Pb年龄及其地质意义

在北祁连西段三岔口等6幅1∶5万区域地质调查中,对祁青构造混杂岩进行了调查研究,通过LA-ICPMS法单颗粒锆石U-Pb同位素测年,获得206Pb/238U表面加权平均年龄494±15Ma,相当于中寒武世,故将该混杂岩解体,部分归为中寒武世黑刺沟组。     

西安地区地裂缝带黄土动力特性试验研究

汾渭盆地是我国乃至世界上地裂缝最为发育,灾害最为严重的地区。考虑到地裂缝灾害对场地条件的影响,尤其是对场地土体的动力特性及动力响应的影响,本文在等压固结条件下,对西安地区地裂缝带黄土进行不同围压下的固结不排水(CU)动三轴试验,获取动力学参数,在此基础上分析了地裂缝带黄土动剪切模量随动剪应变变化特征曲线以及阻尼比随动剪应变变化特征曲线,并对所获得实验曲线进行回归拟合,进而建立了地裂缝带黄土的等效黏弹性动力本构模型,为进一步分析场地土体的动力响应奠定基础。     

庐江-枞阳火山岩矿集区南部城山地区地质条件和成矿规律研究

庐江-枞阳(庐枞)火山岩矿集区南部作为寻找沉积-叠加改造型铁铜矿的有利地区一直没有较大找矿突破,该区近几年勘查取得了一定地质找矿进展。本文主要在野外地质调查的基础上,对庐江-枞阳火山岩矿集区南部城山地区地质条件进行总结分析,重新认识了区内地层的含矿性以及构造特征,发现了大量矿化线索。在研究区内发现了4条与岩浆热液有关的铜铁铅锌矿化带,而且具有一定规律,空间上平面均为北东东、东西向,垂向上从深到浅具有从钼到铜铅锌矿化分带。成矿时间从126.5Ma开始。研究区内大规模磁铁矿化以及铜铅锌矿化的存在,表明深部具有较好找矿潜力。     

蒙古—鄂霍茨克构造带中段构造变形及动力学特征

蒙古—鄂霍茨克构造带作为中亚造山带的重要组成部分,其构造变形和动力学特征一直是地质界关注的问题。沿着该构造带中段,对5个韧性变形点及1个脆性变形点进行详细解析,揭示了该构造带变形及动力学特征。B型褶皱、揉皱、A型褶皱、矿物拉伸线理、S-C组构都显示了该构造带明显的NW—SE剪切作用。剪切方向稳定而单一,未发现多方向变形叠加现象,可能指示了蒙古—鄂霍茨克构造带的形成过程为一期主要的俯冲碰撞或多期同向的俯冲碰撞。对蒙古—鄂霍茨克构造带形成时间和动力学背景进行了讨论,认为该构造带主要形成于中晚侏罗世—早白垩世东亚多向汇聚动力学背景之下。对构造带内地质点mg6脆性断层面上滑动矢量进行了统计和古应力场反演,得出两期古构造应力场,一期为NW—SE挤压,一期为近E—W挤压。NW—SE挤压应力场可能对应了中晚侏罗世—白垩纪古太平洋板块向西俯冲对中亚地区的远程影响;而近E—W向挤压可能反映了早新生代印度—欧亚板块碰撞对中亚地区的远程效应。     

关岭县沙营乡槽子六村一带崩塌（危岩带）特征及防治对策

关岭县北部岗乌永窝大寨6.28特大滑坡碎屑流灾害,造成99人死亡及失踪。通过调查类似地质条件下该地区地质灾害隐患分布情况。以该地区大田小学崩塌为代表分析该类型危岩带形成的原因及形成机理,分析了危岩体稳定性及发展趋势,并运用rockfail软件对滚石运动路径、影响范围、弹跳高度、运动能量做了分析。结合该地区自然条件,提出了相应的防治建议。对该地区类似崩塌（危岩）的防治,有一定的借鉴作用。     

论扬子板块东北缘的俯冲与回撤对山东地块的影响

通过对山东中生代侵入岩体的时空展布、岩石化学及同位素特征的综合分析研究,提出了扬子板块东北缘俯冲与回撤的演化机制,分析了在这种机制下的成岩、成矿演化规律。认为扬子板块东北缘的俯冲与回撤控制了山东中生代的地质演化过程,其回撤在岩石圈深部造成的真空,导致软流圈物质的隆升,是胶东金矿大规模成矿作用的内在控制因素。     

雅鲁藏布江结合带东段仁布-曲松地层分区上三叠统朗杰学(岩)群层序及构造样式再认识

雅鲁藏布江结合带东段夹在南、北两条蛇绿混杂岩带之间的一套活动类型的上三叠统朗杰学(岩)群,许多地质工作者对其地层层序、沉积特征、变形变质、物质来源以及形成的构造环境进行过研究。作者在前人工作成果的基础上,综合对比了已往区调工作获得的实际资料,以(构造)岩石地层为基础,结合沉积古生物特征、变形特征以及区域大地构造背景,对该岩(群)作了进一步的研究。初步认为:朗杰学(岩)群地层层序自老至新为宋热(岩)组、江雄(岩)组和姐德秀(岩)组(章村岩组);郎杰学(岩)群的构造样式为一"Ω"型两翼不对称的复式背斜构造。     

Geochronology and fluid inclusion study of the Yinjiagou porphyry–skarn Mo–Cu–pyrite deposit in the East Qinling orogenic belt,China

The Yinjiagou Mo–Cu–pyrite deposit of Henan Province is located in the Huaxiong block on the southern margin of the North China craton. It differs from other Mo deposits in the East Qingling area because of its large pyrite resource and complex associated elements. The deposit’s mineralization process can be divided into skarn, sulfide, and supergene episodes with five stages, marking formation of magnetite in the skarn episode, quartz–molybdenite, quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite, and calcite–galena–sphalerite in the sulfide episode, and chalcedony–limonite in the supergene episode. Re–Os and ⁴⁰Ar–³⁹Ar dating indicates that both the skarn-type and porphyry-type orebodies of the Yinjiagou deposit formed approximately 143 Ma ago during the Early Cretaceous. Four types of fluid inclusions (FIs) have been distinguished in quartz phenocryst, various quartz veins, and calcite vein. Based on petrographic observations and microthermometric criteria the FIs include liquid-rich, gas-rich, H₂O–CO₂, and daughter mineral-bearing inclusions. The homogenization temperature of FIs in quartz phenocrysts of K-feldspar granite porphyry ranges from 341 °C to >550 °C, and the salinity is 0.4–44.0 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite veins is 382–416 °C, and the salinity is 3.6–40.8 wt% NaCl eqv. The homogenization temperature of FIs in quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite ranges from 318 °C to 436 °C, and the salinity is 5.6–42.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite stockworks is in a range of 321–411 °C, and the salinity is 6.3–16.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–sericite–pyrite is in a range of 326–419 °C, and the salinity is 4.7–49.4 wt% NaCl eqv. The ore-forming fluids of the Yinjiagou deposit are mainly high-temperature, high-salinity fluids, generally with affinities to an H₂O–NaCl–KCl ± CO₂ system. The δ¹⁸O_H2O values of ore-forming hydrothermal fluids are 4.0–8.6‰, and the δD_V-SMOW values are between −64‰ and −52‰, indicating that the ore-forming fluids were primarily magmatic. The δ³⁴S_V-CDT values of sulfides range between −0.2‰ and 6.3‰ with a mean of 1.6‰, sharing similar features with deeply sourced sulfur, implying that the sulfur mainly came from the lower crust composed of poorly differentiated igneous materials, but part of the heavy sulfur came from the Guandaokou Group dolostone. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of sulfides are in the range of 17.331–18.043, 15.444–15.575, and 37.783–38.236, respectively, which is generally consistent with the Pb isotopic signature of the Yinjiagou intrusion, suggesting that the Pb chiefly originated from the felsic–intermediate intrusive rocks in the mine area, with a small amount of lead from strata. The Yinjiagou deposit is a porphyry–skarn deposit formed during the Mesozoic transition of a tectonic regime that is EW-trending to NNE-trending, and the multiepisode boiling of ore-forming fluids was the primary mechanism for mineral deposition.     

Seismic structure of the Helan–Liupan–Ordos western margin tectonic belt in North-Central China and its geodynamic implications

We study high-resolution three-dimensional P-wave velocity (Vp) tomography and anisotropic structure of the crust and uppermost mantle under the Helan–Liupan–Ordos western margin tectonic belt in North-Central China using 13,506 high-quality P-wave arrival times from 2666 local earthquakes recorded by 87 seismic stations during 1980–2008. Our results show that prominent low-velocity (low-V) anomalies exist widely in the lower crust beneath the study region and the low-V zones extend to the uppermost mantle in some local areas, suggesting that the lower crust contains higher-temperature materials and fluids. The major fault zones, especially the large boundary faults of major tectonic units, are located at the edge portion of the low-V anomalies or transition zones between the low-V and high-V anomalies in the upper crust, whereas low-V anomalies are revealed in the lower crust under most of the faults. Most of large historical earthquakes are located in the boundary zones where P-wave velocity changes drastically in a short distance. Beneath the source zones of most of the large historical earthquakes, prominent low-V anomalies are visible in the lower crust. Significant P-wave azimuthal anisotropy is revealed in the study region, and the pattern of anisotropy in the upper crust is consistent with the surface geologic features. In the lower crust and uppermost mantle, the predominant fast velocity direction (FVD) is NNE–SSW under the Yinchuan Graben and NWW–SEE or NW–SE beneath the Corridor transitional zone, Qilian Orogenic Belt and Western Qinling Orogenic Belt, and the FVD is NE–SW under the eastern Qilian Orogenic Belt. The anisotropy in the lower crust may be caused by the lattice-preferred orientation of minerals, which may reflect the lower-crustal ductile flow with varied directions. The present results shed new light on the seismotectonics and geodynamic processes of the Qinghai–Tibetan Plateau and its northeastern margin.