我国西南山区降雨侵蚀力时空变化趋势研究

降雨是我国西南山区土壤侵蚀的主要动力因素,降雨侵蚀力反映了降雨对土壤侵蚀的潜在能力,研究降雨侵蚀力的时空变化趋势对我国西南山区土壤侵蚀的监测、评估、预报和治理具有重要意义。利用1960—2009年129个气象站逐日降雨量资料,计算出西南山区各气象站逐年降雨侵蚀力。采用趋势系数、气候倾向率和克吕格插值等方法对西南山区降雨侵蚀力50年来的时空变化趋势进行了探讨。结果表明:西南山区降雨侵蚀力空间分布特征与年降水量的空间分布特征一致;西南山区西北部的青藏高原区域降雨侵蚀力年际变化明显,变差系数Cv一般高于0.40;西南山区大部地区降雨侵蚀力呈上升趋势,说明由降雨侵蚀力引起的土壤侵蚀风险在增加,但在成都平原附近降雨侵蚀力在明显下降;降雨侵蚀力变化趋势系数随海拔高度升高而不断增加,在海拔2 500 m以上地区尤为明显,西南山区西北部的高海拔地区海拔高度对降雨侵蚀力增加具有放大效应。     

Cambrian Reefs in the Western North China Platform, Wuhai, Inner Mongolia

Mid to late Cambrian thrombolites and maze-like maceriate reefs from the western North China Platform, Wuhai, Inner Mongolia, northwestern China, occur in the middle of a succession dominated by thin-bedded lime mudstone-shale/marlstone alternations, and are laterally surrounded by limestone conglomerate and/or grainstone. Thrombolite, characterized by meter-scale lenticular mounds composed of millimeter- to centimeter-scale mesoclots and wackestone matrix, occurs in the lower middle part of the sequence. Thrombolite mesoclots are composed of microstromatolites with alternating dark gray and light gray micritic laminae. The maze-like maceriate reefs occur in the middle to the upper part of the sequence, commonly forming lenticular mounds up to 1 m thick. They are characterized by centimeter- to decimeter-scale branched maze-like structures, whose biogenic portions (maceria) are selectively dolomitized. The maceriae are composed of poorly preserved microstromatolites and siliceous sponges. Inter-macerial sediments consist of lime mud and scattered bioclasts. These Wuhai reefs are generally similar to but older than various other Cambrian reefs previously reported from the Shandong region, northeastern China.     

内蒙古白乃庙逆冲推覆构造特征及其地质意义

白乃庙逆冲推覆构造自四子王旗北东的十二台向东经白乃庙、博日和延至化德地区,大致沿北纬42°线东西向延伸超过190 km。它发育于华北克拉通与其北侧的奥陶纪白乃庙岛弧带之间,成为华北克拉通与北缘增生带的构造界线,是一套较为典型的陆缘褶冲带。它表现为华北克拉通北缘的中-新元古界白云鄂博群向北逆冲于白乃庙群及其弧后盆地的上志留统徐尼乌苏组和顶志留统西别河组之上。根据构造变形解析并结合音频大地电磁测深资料(CSAMT),得出白乃庙逆冲推覆构造由一系列分支逆断层组成,并向深部于120~800 m处交汇成主底板断层,构成一套叠瓦式逆冲推覆构造,并发育规模不同的构造窗和飞来峰。根据构造窗与飞来峰之间的距离,提出逆冲位移量大于14 km。通过线理及褶皱枢纽统计,指出白乃庙逆冲推覆构造的逆冲方向为自南向北。依据逆冲岩席中发育的断夹块的叠置关系及构造岩的特征,认为其经历了两个期次的活动。对断裂带内同构造形成的包裹石英透镜体的白云母分别进行了Rb-Sr和Ar-Ar同位素测年,认为白乃庙逆冲推覆构造早期活动于450~410 Ma,是白乃庙岛弧带与华北板块碰撞的构造反映。白乃庙逆冲断层晚期活动于晚二叠世至早三叠世,是古亚洲洋最终闭合的构造表现,亦印证研究区经历了印支期构造运动。     

白云鄂博富稀土元素碳酸岩墙的 碳和氧同位素特征

重点解剖了一条距白云鄂博超大型REE-Nb-Fe矿床东矿北东方向2 k m、切割白云鄂 博群H1及H3岩性段的细粒方解石碳酸岩岩墙的碳和氧同位素地球化学特征。结果表明,碳酸 岩的碳同位素组成变化范围较小(δ13C值为－6.6‰ ～ －4.6‰),与正常地幔碳δ 13C值－5±2‰一致;而氧同位素组成变化范围较大(δ18O值为11.9‰～17.7‰ ),显著高于地幔的δ18O值5.7±1.0‰,表明碳酸岩浆在结晶过程中或之后曾与 低 温热液流体发生了同位素交换。碳酸岩墙中白云石与方解石之间的碳和氧同位素分馏均小于 0‰,处于不平衡状态,说明该碳酸岩墙中的白云石与方解石并非同成因矿物,白云石可能 为次生成因的。     

内蒙古长山壕金矿矿床地球化学特征与成因研究

长山壕金矿是近年来在内蒙古中部发现的一个大型浅变质碎屑岩型金矿,产于中—新元古代白云鄂博群比鲁特组碳质板岩和千枚岩中,矿体与围岩呈渐变关系。矿石呈硫化物细脉和石英硫化物细脉状,产于地层层理、节理和破碎带中,与地层同步褶皱变形。矿石的微量元素特征与围岩一致,矿石铅同位素为208Pb/204Pb为37.430 8～38.9792,207Pb/204Pb为15.452 2～15.674 1,206Pb/204Pb为17.109～18.921 7,与地层铅同位素接近。流体包裹体以液相包裹体为主,均一温度230～370℃,平均286.8℃;盐度w(NaCl)为6.01%～20.52%,平均10.84%;包裹体水的δD为-108‰～-112‰,δ18O为6.4‰～9.4‰。地质地球化学特征表明成矿物质来自地层,成矿热液主要来自地层水。研究认为长山壕金矿为沉积-变质型金矿,后期的岩浆活动对成矿作用影响较小。     

水岩作用对内蒙古南部砒砂岩风化侵蚀的影响分析

砒砂岩是指在内蒙古东胜至准格尔旗一带,发育于三叠纪、侏罗纪、白垩纪时期的一套河流相碎屑岩沉积,是黄河中游集中的基岩产沙区和粗泥沙的主要来源地之一。通过野外调查、样品采集和测试、水岩作用模拟等方法,分析雨水对岩石风化侵蚀的影响。对水样品测试结果的逆向模拟显示雨水对砒砂岩主要有3个方面的作用：(1)减小岩体内部粘结力,增加岩体孔隙度,促使方解石、长石、白云石、石膏和岩盐等溶解,使得岩体内孔隙度增大;(2)发生化学溶蚀,长石等矿物易于风化成高岭石、钙蒙脱石,扩大岩体中的裂隙;(3)钙蒙脱石的沉淀量较大,其遇水即膨胀的特性会给岩体内部增大压力而破坏岩石结构。水岩作用影响了砒砂岩的物理力学性质,加剧了砒砂岩风化与侵蚀。      

内蒙古牙克石喇嘛山花岗岩景观特征及其对比分析

内蒙古牙克石市喇嘛山有海西期至燕山期白岗质花岗岩岩组和花岗斑岩岩组出露.受新华夏构造体系波及,塑性地层发生褶皱,刚性岩层断裂,形成区内大小28座突兀挺拔、陡峭嶙峋的花岗岩奇峰;又由于该区气候湿润,岩石风化、溶蚀较快,周围岩石脱落,导致各种类型的花岗岩峰石球化,形成大量石蛋、石柱、象形石、石槽、岩臼、石穴等微地貌.本文简要叙述了喇嘛山花岗岩景观的类型、特征,并与其他地区典型花岗岩地貌景观进行了对比分析.     

A rare earth element-rich carbonatite dyke at Bayan Obo, Inner Mongolia, North China

Summary ?A carbonatite dyke, extremely enriched in rare earth elements (REE), is reported from Bayan Obo, Inner Mongolia, North China. The REE content in the dyke varies from 1 wt% to up to 20 wt%. The light REEs are enriched and highly fractionated relative to the heavy REEs, and there is no Eu anomaly. Although carbon isotope δ¹³C (PDB) values of the carbonatites (−7.3 to −4.7‰) are within the range of normal mantle (−5±2‰), oxygen isotope δ¹⁸O (SMOW) (11.9 to 17.7‰) ratios apparently are higher than those of the mantle (5.7±1.0‰), indicating varying degrees of exchange with hydrothermal fluids during or after magmatic crystallization. The carbonatite is the result of partial melting followed by fractional crystallization. Primary carbonatite melt was formed by less than 1% partial melting of enriched mantle, leaving a garnet-bearing residue. The melt then rose to a crustal magma chamber and underwent fractional crystallization, producing further REE enrichment. The REE and trace element distribution patterns of the carbonatites are similar to those of fine-grained dolomite marble, the ore-host rock of the Bayan Obo REE–Nb–Fe giant mineral deposit. This fact may indicate a petrogenetic link between the dykes described here and the Bayan Obo mineral deposit. Received November 1, 2001; revised version accepted June 16, 2002     

Geological and Geochemical Characteristics of the Zhulazhaga Gold Deposit in Inner Mongolia, China

Located in Alxa Zuoqi (Left Banner) of Inner Mongolia, China, the Zhulazhaga gold deposit is the first largescale gold deposit that was found in the middle-upper Proterozoic strata along the north margin of the North China craton in recent years. It was discovered by the No. l Geophysical and Geochemical Exploration Party of Inner Mongolia as a result of prospecting a geochemical anomaly. By now, over 50 tonnes of gold has been defined, with an average Au grade of 4 g/t. The ore bodies occur in the first lithological unit of the Mesoproterozoic Zhulazhagamaodao Formation (MZF), which is composed mainly of epimetamorphic sandstone and siltstone and partly of volcanic rocks. With high concentration of gold,the first lithological unit of the MZF became the source bed for the late-stage ore formation. Controlled by the interstratal fracture zones, the ore bodies mostly appear along the bedding with occurrence similar to that of the strata. The primitiveore types are predominantly the altered rock type with minor ore belonging to the quartz veins type. There are also some oxidized ore near the surface. The metallic minerals are composed mainly of pyrite, pyrrhotite and arsenopyrite with minor chalcopyrite, galena and limonite. Most gold minerals appear as native gold and electrum. Hydrothermal alterations associated with the ore formation are actinolitization, silicatization, sulfidation and carbonation. A total of 100 two-phase H2O-rich and 7 three-phase daughter crystal-beating inclusions were measured in seven goldbearing quartz samples from the Zhulazhaga gold deposit. The homogenization temperatures of the two-phase H2O-rich inclusions range from 155 to 401℃, with an average temperature of 284℃ and bimodal distributions from 240 to 260℃ and 300 to 320℃ respectively. The salinities of the two-phase H2O-rich inclusions vary from 9.22wt% to 24.30wt% NaCl eqniv, with a mode between 23 wt% and 24wt% NaC1 equiv. Comparatively, the homogenization temperatures of the threephase daughter crystal-beating inclusions vary from 210 to 435℃ and the salinities from 29.13wt% to 32.62wt% NaCl equiv. It indicates that the ore-forming fluid is meso-hypothermal and characterized by high salinity, which is apparently different from the metamorphic origin with low salinity. It suggests a magmatic origin of the gold-bearing fluid. The δ^18O values of quartz from auriferous veins range from 11.9 to 16.3 per mil, and the calculated δ^18OH2O values in equilibrium with quartz vary from 1.06 to 9.60 per mil, which fall between the values of meteoric water and magmatic water. It reflects that the ore-forming fluid may be the product of mixing of meteoric water and magmatic water.Based on geological and geochemical studies of the Zhulazhaga gold deposit, it is supposed that the volcanism in the Mesoproterozoic might make gold pre-concentrate in the strata. The extensive and intensive Hercynian tectono-magmatic activity not only brought along a large number of ore-forming materials, but also made the gold from the strata rework. It can be concluded that the ore bodies were mainly formed in late hydrothermal reworking stage. Compared with typical gold deposits associated with epimetamorphic clastic rocks, the Zhulazhaga deposit has similar features in occurrence of ore bodies, ore-controlling structure, wall-rock alterations and mineral assemblages. Therefore, the Zhulazhaga gold deposit belongs to the epimetamorphic clastic rock type.     

Geological Characteristics and Origin of the Hashitu Molybdenum Deposit, Inner Mongolia, China

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