甘肃阿克塞县安南坝地区镁铁质麻粒岩锆石U-Pb年龄和Hf同位素组成:对塔里木东南缘前寒武纪地质演化的启示          下载免费PDF全文

辜平阳  徐学义  何世平  赵惠博  庄玉军  查显锋  陈锐明  郭亚鹏 《地质科学》2019,54(2):549-570

甘肃阿克塞县安南坝地区镁铁质麻粒岩呈脉状或透镜状赋存于新太古代米兰岩群和TTG片麻岩中。岩石主要由斜方辉石（Opx）+单斜辉石（Cpx）+角闪石（Amp）+斜长石（Pl）+磁铁矿（Mt）等组成,具有典型中-低压麻粒岩相岩石的矿物组合特征。LA-ICP-MS锆石U-Pb测年结果显示镁铁质麻粒岩原岩形成时代可能为2 561±29 Ma,与塔里木东南缘2.6～2.5 Ga岩浆作用时代基本一致,说明新太古代晚期是塔里木东南缘重要的陆壳增生期。此外,通过测年还获得了～1.95 Ga、～1.86 Ga两期变质年龄。其中,～1.95 Ga的峰期变质年龄是塔里木克拉通东南缘古元古代晚期强烈构造—热事件的地质记录。～1.86 Ga的变质年龄可能与该地区古元古代末期构造—岩浆事件密切相关。镁铁质麻粒锆石¹⁷⁶Hf/¹⁷⁷Hf比值均＜0.281 621,ε_Hf(t) 值为-14.08～3.12,两阶段模式年龄（T_DM2）主要集中在～2.65 Ga,指示其原岩岩浆起源于新太古代富集岩石圈地幔。  相似文献   

北大别罗田榴辉岩的减压出溶结构与超高压变质作用   总被引：1，自引：0，他引：1       下载免费PDF全文

刘贻灿  古晓锋  陈振宇 《地质科学》2009,44(1):202-212

岩石学研究表明北大别罗田榴辉岩经过了榴辉岩相、麻粒岩相和角闪岩相变质作用,表现出多种减压出溶结构.特征性的减压出溶结构有单斜辉石和石榴石中分别发育石英+角闪石+斜长石等与金红石+单斜辉石+角闪石等针状矿物出溶体,以及锆石中含有柯石英残晶.这些进一步证明北大别南部（罗田一带）同北部（如黄尾河、百丈岩等地）榴辉岩一样经过了>5～7CPa的超高压变质作用.  相似文献   

The missing half of the subduction factory: shipboard results from the Izu rear arc,IODP Expedition 350     

Cathy J. Busby  Yoshihiko Tamura  Peter Blum  Gilles Guèrin  Graham D. M. Andrews  Abigail K. Barker 《International Geology Review》2017,59(13):1677-1708

IODP Expedition 350 was the first to be drilled in the rear part of the Izu-Bonin, although several sites had been drilled in the arc axis to fore-arc region; the scientific objective was to understand the evolution of the Izu rear arc, by drilling a deep-water volcaniclastic section with a long temporal record (Site U1437). The Izu rear arc is dominated by a series of basaltic to dacitic seamount chains up to ~100-km long roughly perpendicular to the arc front. Dredge samples from these are geochemically distinct from arc front rocks, and drilling was undertaken to understand this arc asymmetry. Site U1437 lies in an ~20-km-wide basin between two rear arc seamount chains, ~90-km west of the arc front, and was drilled to 1804 m below the sea floor (mbsf) with excellent recovery. We expected to drill a volcaniclastic apron, but the section is much more mud-rich than expected (~60%), and the remaining fraction of the section is much finer-grained than predicted from its position within the Izu arc, composed half of ashes/tuffs, and half of lapilli tuffs of fine grain size (clasts <3 cm). Volcanic blocks (>6.4 cm) are only sparsely scattered through the lowermost 25% of the section, and only one igneous unit was encountered, a rhyolite peperite intrusion at ~1390 mbsf. The lowest biostratigaphic datum is at 867 mbsf (~6.5 Ma), the lowest palaeomagnetic datum is at ~1300 mbsf (~9 Ma), and the rhyolite peperite at ~1390 mbsf has yielded a U–Pb zircon concordia intercept age of (13.6 + 1.6/?1.7) Ma. Both arc front and rear arc sources contributed to the fine-grained (distal) tephras of the upper 1320 m, but the coarse-grained (proximal) volcaniclastics in the lowest 25% of the section are geochemically similar to the arc front, suggesting arc asymmetry is not recorded in rocks older than ~13 Ma.  相似文献   

江西朱溪铜钨矿床成因:来自矿物学和年代学的启示   总被引：1，自引：0，他引：1  

贺晓龙  张达  陈国华  狄永军  霍海龙  李宁  张志辉  饶建锋  魏锦  欧阳永棚 《吉林大学学报(地球科学版)》2018,48(4):1050-1070

江西景德镇朱溪铜钨矿床是近年来发现的一个世界级超大型铜钨矿床。矿床地质特征、矽卡岩矿物学和成矿岩体年代学的研究表明,矿体赋存于上石炭统黄龙组大理岩与新元古界双桥山群变质岩之间的不整合界面之上,空间上具有明显的矿物组合分带特征。根据矽卡岩产状、矿物共生组合和相互关系,把成矿作用划分为矽卡岩阶段、退化蚀变阶段、石英-硫化物阶段、碳酸盐-萤石阶段。代表性的矽卡岩矿物组合有石榴子石、透辉石、透闪石、硅灰石、符山石、蛇纹石、绿泥石等。电子探针分析表明,石榴子石为钙铝榴石—钙铁榴石系列,辉石为透辉石—钙铁辉石系列。同位素年代学及岩浆与成矿关系的研究表明：花岗闪长岩与早期矽卡岩型矿化相关,矿化范围较小,矿石品位较低;黑云母花岗岩与云英岩型和晚期矽卡岩型的矿化相关,矿化范围较广,矿石品位较高,并获得黑云母花岗岩LA-ICP-MS锆石U-Pb年龄为（147.7±2.2）Ma。综合分析指出,朱溪铜钨矿床为晚侏罗世花岗岩浆有关的热液与晚古生代碳酸盐岩发生多阶段交代作用而形成,成矿作用以矽卡岩型和云英岩型为主。  相似文献   

Hydrochemistry,multidimensional statistics,and rock mechanics investigations for Sanshandao Gold Mine,China     

Hongyu Gu  Fengshan Ma  Jie Guo  Kepeng Li  Rong Lu 《Arabian Journal of Geosciences》2017,10(3):62

Prediction of bursting water in a submarine mine (Sanshandao Gold Mine) is very important. The aim of this study was to understand the water sources, mixing ratios, and flow paths in a mining region by using hydrochemistry, principal component analysis (PCA), and rock mechanics. Field observations reveal that there are unusual geothermal gradients and complicated geological conditions. Samples collected from the surface and every depth of the tunnel were analyzed for various ions and isotopes (¹⁸O and D). PCA was used to identify the most likely water sources on the foundation of hydrochemistry and a conceptual model. Four kinds of water sources were identified: (1) water mixture of surface freshwater and seawater, (2) brine derived from a deep closed environment, (3) thermal brine derived from the northwestern fault (F3), and (4) Quaternary water. The water sources were variable with time at a sampling site. The combination of water sources in a specific sampling campaign can be decided by the positive scores on principal components (PCs). The PCA results indicate that the first and the fourth kind of water source appear in the deep tunnel with the continual mining activity. Mixing ratio calculations for each sampling campaign show that the first and the fourth kind of water source constitute a small proportion of the total water. The main water sources are the second and third kinds of water. Finally, water flow paths were determined based on the PCA, and rock mechanics is used to explain the change in the water flow paths after excavation. The results show the following: (1) There are several strong water diversion zones that distribute at a certain spacing interval on the large scale and (2) “zonal disintegration” is also found in the tunnel. The fractured zone and the non-fractured zone appear in turn around the tunnel. The rock mass in these two zones represents the tensile and compressive properties, respectively. Thus, volumes of water and permeability of joints and fractures in these two zones are great different.  相似文献   

Temporal variation of intertidal seagrass in southern China (2008–2014)     

Guanglong Qiu  Frederick T. Short  Hangqing Fan  Guohua Liu 《Ocean Science Journal》2017,52(3):397-410

Understanding the temporal dynamics of seagrasses and the major influences on seagrass growth is critical for seagrass habitat conservation and administration. However, little work has been done regarding these issues in southern China. To examine inter-annual and seasonal variations of the intertidal Halophila ovalis community in southern China, we conducted quarterly sampling using the SeagrassNet methodology and assessed environmental conditions as well as direct anthropogenic impacts on the seagrass meadow from July 2008 to October 2014. Our study demonstrated strong inter-annual and seasonal dynamics of the intertidal seagrass meadow in the study area. Generally, the community performed best (highest seagrass cover, leaf area, shoot density, total biomass) in summer and worst in spring among the 4 seasons. The temporal variations in the seagrass community attributes (e.g. above-ground biomass) were significantly affected by precipitation, atmospheric visibility, and salinity, while leaf width was significantly negatively correlated with temperature, atmospheric visibility and salinity. Temperature was a major factor influencing the seagrass community (both macroalgae and seagrass), with temperature data showing an inverse relationship between seagrass and macroalgae. The above-ground: below-ground biomass ratio and leaf width of H. ovalis were the most sensitive plant parameters monitored when assessing environmental interactions. Human physical disturbances did not have a significant effect on seagrass dynamics in the study area. We concluded that long-term monitoring (like SeagrassNet) is valuable in understanding the relationship between environmental variables and seagrasses.  相似文献   

内蒙古双尖子山银多金属矿床花岗斑岩年代学、地球化学特征及构造意义   总被引：2，自引：0，他引：2  

顾玉超 《地质与勘探》2017,53(3):495-507

本文对内蒙古双尖子山银多金属矿床花岗斑岩进行了锆石SHRIMP U-Pb定年,并对花岗斑岩的主量元素、微量元素组成进行了分析研究。结果显示,双尖子山花岗斑岩加权平均年龄为(133.4±1.2)Ma,为大兴安岭南段早白垩世岩浆活动集中期产物;花岗斑岩SiO_2含量为68.81%~70.05%,低MgO、TiO_2,K_2O/Na_2O为0.97~1.27,较为富钾;A/CNK在0.94~1.12之间,属准铝-弱过铝系列;富集Rb、Th、U、K等大离子亲石元素(LILE),亏损Sr、P、Ti等高场强元素(HFSE);稀土总量ΣREE中等,δEu为0.55~0.62,Eu中等负异常。本文认为双尖子山银多金属矿床为多期次叠加的岩浆热液型矿床,160Ma和133Ma可能分别是岩浆活动的两个高峰期。花岗斑岩形成于陆内晚造山期-造山期后的伸展环境,蒙古-鄂霍次克洋俯冲板片在深部断离,引发软流圈物质上涌,这是导致大兴安岭南段早白垩世岩石圈伸展环境的主要机制。  相似文献   

Compositional dual mesh method for single phase flow in heterogeneous porous media—application to CO<Subscript>2</Subscript> storage     

Dominique Guérillot  Jérémie Bruyelle 《Computational Geosciences》2017,21(5-6):949-961

Numerical simulation of fluid flow coupled with chemical reactions has been an active field in the hydrogeology community and many formulations have been programmed into different software. In recent years, this subject has attracted increasing interest in the reservoir simulation community, partly for the application of chemical methods for hydrocarbon extraction but also for research on the geological sequestration of CO₂. In this paper, an extension to the concept of dual mesh for reactive transport modeling is presented. This approach involves two meshes, a low-resolution mesh to resolve the pressure equation and a high-resolution mesh to transport the species and to calculate the geochemical equilibrium. The main objective is to preserve the fine scale heterogeneities to reach a more accurate field behavior simulation than conventional approach which consist in performing simulations on a coarser mesh. The method is applied to a simulation of CO₂ storage in the SPE10 model that keep a high resolution of the heterogeneities.  相似文献   

Understanding the triggering mechanism and possible kinematic evolution of a reactivated landslide in the Three Gorges Reservoir   总被引：2，自引：0，他引：2  

Dong Ming Gu  Da Huang  Wei Dong Yang  Ji Liang Zhu  Guo Yang Fu 《Landslides》2017,14(6):2073-2087

More than 5000 landslides or potential landslides have been induced in the Three Gorges Reservoir (TGR) region since the impoundment in 2003, which have caused great damage and remain a huge threat to the dam and people living in the reservoir area. Understanding the deformation characteristics and failure mechanism of the landslides can be helpful in stability evaluation and landslide prediction. The primary aim of this study is to research the characteristics of the landslide motion and its relationships with environmental triggers, taking the Quchi landslide, a large, slow-moving, reactivated landslide in the TGR region, as an example. The instability clearly showed visible signs of movements since 2002, and after that, the slope has been experiencing persistent deformation. By combining 4 years of meteorological, hydrological data with displacement measurements from open fractures, deep boreholes, and surface points, as well as in situ observations, this paper reports the geological and geotechnical investigations performed to define the movement. The deformation is believed to be governed by reservoir water levels, while the precipitation has a minor effect. Seasonally, the slope movement has a very distinctive pattern with large deformation starting abruptly right after reservoir drawdown in June and lasting into late summer (September). Then there is a rapid transition to constant deformation (almost no displacement) as the reservoir level rises. The slope displacements appear to gradually increase every year, which suggests very high possibility of the large and overall failure of the slide. Both monitoring results and geomorphological observations have highlighted that the two active slide masses Q1 and Q2 would probably collapse in different kinematic evolution modes, i.e., the multistage failure and whole sliding motion.  相似文献   

四川盆地中二叠统栖霞组、茅口组岩相古地理及勘探方向     

厚刚福  周进高  谷明峰  姚倩颖  杨柳  潘立银  郝毅 《海相油气地质》2017,22(1)

通过地层剥蚀关系分析,四川盆地中二叠统沉积前的古构造格局具有"三隆一洼"的特点。基于野外剖面、岩心和薄片观察,结合录井、测井相和地震相分析,明确了栖霞组和茅口组发育镶边碳酸盐岩台地沉积,包含一级台缘带、二级台缘带、开阔台地和台盆等4种亚相以及一级台缘滩、二级台缘滩、台内滩和硅质台盆等微相。栖霞组、茅口组岩相古地理受控于沉积前古构造:一级台缘带分布于古隆起与斜坡—盆地过渡地带;开阔台地分布于古隆起区和低隆起区;台盆分布于低洼区;二级台缘带分布于开阔台地和台盆之间的过渡地带。类比上二叠统长兴组和下三叠统飞仙关组油气勘探,栖霞组、茅口组台地内部的二级台缘带可作为下一步油气勘探的有利领域。  相似文献