北祁连山东段新元古代火山岩的年代学证据

在1∶5万石门川幅、老龙湾幅区域地质调查时发现,北祁连山东段上吊吊坡地区存在一套不同于下奥陶统阴沟群的火山岩,经全岩样品Sm-Nd同位素测定,获得Sm-Nd等时线年龄为(723±25.0)Ma,表明其形成时代为新元古代。地球化学特征表明该套火山岩形成于岛弧环境,说明当时北祁连东段仍处于洋壳俯冲挤压环境。     

秦岭造山带成矿作用概述

对区域成矿背景、区域成矿元素地球化学背景、构造 -成矿体系、矿床区域成矿模式进行了讨论 ,在对大量资料研究的基础上提出了作者的认识。     

六盘山典型植被类型土壤中石砾对大孔隙形成的影响

六盘山山区土壤中存在大量的石砾,对土壤大孔隙的形成具有重要影响。为了深刻了解和评价土壤中石砾对大孔隙形成的可能作用,本研究分析了六盘山典型植被类型下土壤中的石砾体积含量、大孔隙度变异以及石砾体积含量对大孔隙度、大孔隙半径与密度的影响。结果表明,石砾含量增加导致土壤大孔隙的平均半径和体积增大,特别是导致半径大于1.4 mm的大孔隙密度的增大,但对较小半径的大孔隙密度影响不大;总体上,石砾对土壤大孔隙度的形成影响随土深的增加而越来越明显,说明六盘山地区土壤的大孔隙明显同时受到生物因素和石砾含量因素的影响。     

龙门山中段彭灌断裂带汶川Ms8.0地震同震破裂断层识别及其浅、表构造特征

2008年汶川Ms8.0地震在龙门山中段的彭灌断裂带产生的地表破裂,是该地震产生的第二大地表破裂带.综合应用地质、钻井以及二维、三维地震数据,利用横贯前山带的多条人工地震反射剖面,对彭灌断裂带产生同震破裂的断层进行准确识别和解释.研究表明,龙门山中段的彭灌断裂带是一套由3条主要断层和次级广泛发育的断裂组合构成,浅层表现...     

New Mexico structural zone—an analogue of the Colorado mineral belt

Updated aeromagnetic maps of New Mexico together with current knowledge of the basement geology in the northern part of the state (Sangre de Cristo and Sandia–Manzano Mountains)—where basement rocks were exposed in Precambrian-cored uplifts—indicate that the northeast-trending Proterozoic shear zones that controlled localization of ore deposits in the Colorado mineral belt extend laterally into New Mexico. The shear zones in New Mexico coincide spatially with known epigenetic precious- and base-metal ore deposits; thus, the mineralized belts in the two states share a common inherited basement tectonic setting. Reactivation of the basement structures in Late Cretaceous–Eocene and Mid-Tertiary times provided zones of weakness for emplacement of magmas and conduits for ore-forming solutions. Ore deposits in the Colorado mineral belt are of both Late Cretaceous–Eocene and Mid-Tertiary age; those in New Mexico are predominantly Mid-Tertiary in age, but include Late Cretaceous porphyry-copper deposits in southwestern New Mexico.The mineralized belt in New Mexico, named the New Mexico structural zone, is 250-km wide. The northwest boundary is the Jemez subzone (or the approximately equivalent Globe belt), and the southeastern boundary was approximately marked by the Santa Rita belt. Three groups (subzones) of mineral deposits characterize the structural zone: (1) Mid-Tertiary porphyry molybdenite and alkaline-precious-metal deposits, in the northeast segment of the Jemez zone; (2) Mid-Tertiary epithermal precious-metal deposits in the Tijeras (intermediate) zone; and (3) Late Cretaceous porphyry-copper deposits in the Santa Rita zone. The structural zone was inferred to extend from New Mexico into adjacent Arizona. The structural zone provides favorable sites for exploration, particularly those parts of the Jemez subzone covered by Neogene volcanic and sedimentary rocks.     

大兴安岭十八站—韩家园地区晚中生代火山岩年龄、地球化学特征及其构造意义

大兴安岭十八站—韩家园地区发育晚中生代基性-中酸性火山岩。选取粗面安山岩、粗面岩、流纹岩进行年代学和岩石地球化学研究。粗面安山岩LA-ICP-MS锆石U-Pb年龄为125.2±0.9 Ma,为早白垩世火山作用的产物。岩石地球化学特征表明,中酸性火山岩属于高钾钙碱性-钾玄岩系列。岩石稀土元素总量∑REE=121.42×10~(-6)~154.43×10~(-6),轻、重稀土元素分异明显(La/Yb)_N=19.25~31.98,在稀土元素配分图上显示右倾型,除一个流纹岩样品具显著负Eu异常外,多数样品无明显Eu负异常(δEu=0.45~0.90)。岩石具弱富集大离子亲石元素Ba、Sr,明显亏损高场强元素Nb、Ta、Ti的特征。结合区域资料,认为十八站—韩家园地区早白垩世中酸性火山岩形成于蒙古-鄂霍茨克洋闭合机制下后碰撞伸展背景。粗面安山岩、粗面岩和流纹岩系同源岩浆部分熔融与结晶分异作用的结果,岩浆来源于受俯冲流体交代的富集岩石圈地幔。     

大别山北缘石炭系碎屑岩地球化学及碎屑锆石年代学分析及其对物源区大地构造属性判别的制约

大别山北缘石炭系作为古生代唯一不变质或轻微变质的沉积地层,记录了其物源信息和古生代的构造演化.针对研究区这一地质特征,本文分析了研究区砂岩的碎屑组分、常量元素、微量元素和稀土元素,以及碎屑锆石的同位素年龄,并据此对物源区的大地构造属性进行了研究.研究区碎屑岩主要以中细粒石英砂岩和长石石英砂岩为主,砂岩的QFL平均值为Q 76.2％,F 15.9％,L7.9％,Q/(F+ L) 4.26;主要元素氧化物平均百分含量SiO263.69％,Al2O3 11.25％,MgO 3.66％,CaO 5.15％,Fe2O3T 6.15％,K2O 1.68％,Na2O 0.68％;部分特征微量元素Th,U,Hf,Sc,Zr,Y平均含量分别为10.78×10-6、2.64×10-6、4.39×10-6、15.67×10-6、166×10-6、25.33×10-6.Rb/Sr,Th/U,La/Y,La/Sc,Th/Sc比值分别为1.49、4.10、14.75、31.92和0.89;稀土元素总量ΣREE平均146.2×10-6(54.11×10-6 ～256.0×10-6),Eu异常0.64,轻稀土略有富集,La/Yb为12.58(3.94～15.42),(La/Yb)N为9.02.锆石年龄测定表明,早石炭世地层中碎屑锆石的年龄主要集中在400 ～500Ma,晚石炭世地层中碎屑锆石年龄主要为900～ 1300Ma,其次为2000～ 2800Ma.上述结果表明大别山北缘石炭系沉积物来源于不同的源区,包括早古生代的大陆岛弧、扬子板块中-新元古代基底以及华北板块古-中元古代基底.     

北秦岭火山岩岩石化学特征和成因

北秦岭存在A、B、C三类火山岩系列,对应着幔源型、壳幔混染型和壳幔混合型成因类型。火山岩系列和成因类型的系统变化,反映了多旋回壳幔物质迁移特证。     

Landslides in the Central Coalfield (Cantabrian Mountains, NW Spain): Geomorphological features, conditioning factors and methodological implications in susceptibility assessment

A geomorphological study focussing on slope instability and landslide susceptibility modelling was performed on a 278 km² area in the Nalón River Basin (Central Coalfield, NW Spain). The methodology of the study includes: 1) geomorphological mapping at both 1:5000 and 1:25,000 scales based on air-photo interpretation and field work; 2) Digital Terrain Model (DTM) creation and overlay of geomorphological and DTM layers in a Geographical Information System (GIS); and 3) statistical treatment of variables using SPSS and development of a logistic regression model. A total of 603 mass movements including earth flow and debris flow were inventoried and were classified into two groups according to their size. This study focuses on the first group with small mass movements (10⁰ to 10¹ m in size), which often cause damage to infrastructures and even victims. The detected conditioning factors of these landslides are lithology (soils and colluviums), vegetation (pasture) and topography. DTM analyses show that high instabilities are linked to slopes with NE and SW orientations, curvature values between − 6 and − 0.7, and slope values from 16° to 30°. Bedrock lithology (Carboniferous sandstone and siltstone), presence of Quaternary soils and sediments, vegetation, and the topographical factors were used to develop a landslide susceptibility model using the logistic regression method. Application of “zoom method” allows us to accurately detect small mass movements using a 5-m grid cell data even if geomorphological mapping is done at a 1:25,000 scale.     

大兴安岭摩天岭雨养泥炭沼泽多环芳烃分布特征与来源分析

运用气相色谱—质谱(GC-MS)技术对大兴安岭摩天岭(47°22′23″N,120°38′45″E)雨养泥炭沼泽泥炭柱中的多环芳烃(PAHs)污染物进行了分析。结果表明,研究区雨养泥炭沼泽表层PAHs总含量的质量比为1 874.4 ng/g,与国内外雨养泥炭沼泽表层相比,其污染水平相对较高。由于研究区气候冷湿,雨养泥炭沼泽中的有机质腐殖化程度较低,有机碳含量较高,这和其PAHs含量的相关性较小。研究区样品中检测出的PAHs主要以2~3环的多环芳烃为主;由PAHs分子标志物指标分析结果可知,研究区雨养泥炭沼泽PAHs污染物的主要来源是当地森林火灾与大气远距离沉降;沉降的PAHs污染物是原油开采、石油生产和化石燃料燃烧的共同贡献。在距地表15~34 cm处,柱状剖面层的PAHs含量显著增加,这是由于1987年和1998年大兴安岭发生森林火灾树木燃烧所致。