Crustal structure of the Ruby Mountains and southern Carlin Trend region, Nevada, from magnetotelluric data

We have collected about 150 magnetotelluric (MT) soundings in northeastern Nevada in the region of the Ruby Mountains metamorphic core complex uplift and southern Carlin mineral trend, in an effort to illuminate controls on core complex evolution and deposition of world-class gold deposits. The region has experienced a broad range of tectonic events including several periods of compressional and extensional deformation, which have contributed to the total expression of electrical resistivity. Most of the soundings reside in three east–west profiles across increasing degrees of core uplift to the north (Bald Mountain, Harrison Pass, and Secret Pass latitudes). One short cross-line was also taken to assess an east–west structure to the north of the northern profile. Model resistivity cross-sections were derived from the MT data using a 2-D inversion algorithm, which damps departures of model parameters from an a priori structure. Geological interpretation of the resistivity combines previous seismic, potential field and isotope models, structural and petrological models for regional compression and extension, and detailed structural/stratigraphic interpretations incorporating drilling for petroleum and mineral exploration. To first order, the resistivity structure is one of a moderately conductive, Phanerozoic sedimentary section fundamentally disrupted by intrusion and uplift of resistive crystalline rocks. Late Devonian and early Mississippian shales of the Pilot and Chainman Formations together form an important conductive marker sequence in the stratigraphy and show pronounced increases in conductance (conductivity–thickness product) from east to west. These increases are attributed to graphitization caused by Elko–Sevier era compressional shear deformation and possibly by intrusive heating. The resistive crystalline central massifs adjoin the host stratigraphy across crustal-scale, steeply dipping fault zones. The zones provide pathways to the lower crust for heterogeneous, upper crustal induced, electric current flow. Resistive core complex crust appears steeply bounded under the middle of the neighboring grabens and not to deepen at a shallow angle to arbitrary distances to the west. The numerous crustal breaks imaged with MT may contribute to the low effective elastic thickness (T_e) estimated regionally for the Great Basin and exemplify the mid-crustal, steeply dipping slip zones in which major earthquakes nucleate. An east–west oriented conductor in the crystalline upper crust spans the East Humboldt Range and northern Ruby Mountains. The conductor may be related to nearby graphitic metasediments, with possible alteration by middle Tertiary magmatism. Lower crustal resistivity everywhere under the profiles is low and appears quasi one-dimensional. It is consistent with a low rock porosity (<1 vol.%) containing hypersaline brines and possible water-undersaturated crustal melts, residual to the mostly Miocene regional extension. The resistivity expression of the southern Carlin Trend (CT) in the Pinon Range is not a simple lineament but rather a family of structures attributed to Eocene intrusion, stratal deformation, and alteration/graphitization. Substantial reactivation or overprinting by core complex uplift or Basin–Range extensional events seems likely. We concur with others that the Carlin Trend may result in part from overlap of the large Eocene Northeast Nevada Volcanic Field with Precambrian–Paleozoic deep-water clastic source rocks thickening abruptly to the west of the Pinon Range, and projecting to the north–northwest.     

川西龙门山前陆盆地晚新生代沉积记录与构造响应

龙门山前陆盆地位于青藏高原东缘,夹于龙门山推覆造山带与龙泉山褶断带之间。自4.6 Ma以来,逆冲推覆构造运动使龙门山造山带强烈隆升,古河流的侵蚀、搬运和堆积作用使盆地沉积了1套巨厚的半固结—松散堆积物。通过对沉积特征和沉积结构的综合研究,认为龙门山前陆盆地是由自东向西的深部多级俯冲潜滑而引起的浅部由西向东的多层次推覆作用形成的,其晚新生代逆冲推覆构造所产生的构造负载是龙门山前陆盆地的成盆动力。岩浆物质的循环过程表明成都盆地在形成过程中遵循物质循环与能量守恒定律。龙门山前陆盆地地质构造的沉积响应表现为:沉积基底整体上向西倾斜,盆地剖面明显不对称;沉积地层与下伏地层均为不整合接触;盆内发育了一系列相间排列的次级凹陷和凸起,并呈雁斜式展布;砾质粗碎屑楔状体的周期性发育。从盆地动力学的角度初步分析了龙门山前陆盆地盆-山耦合关系,龙门山冲断带及其前陆盆地的研究对于大地构造位置、成矿作用以及油气聚集地的勘探等具有重要意义。     

从阿巴拉契亚-阿钦塔造山带看中国北方大陆南缘古生代的油气前景

阿巴拉契亚-阿钦塔造山带是北美乃至世界著名的大陆边缘挤压碰撞推覆造山带,是地质学研究的经典地区之一,也是许多经典地学理论和概念的发源地.其中,对地质学影响最大的当属地槽学说.继20世纪60年代由深海钻探带来地学革命之后,由COCORP实施的地震反射剖面和深钻揭示了该造山带的巨大推覆构造.人们惊奇地发现,在巨大推覆体之下...     

辽宁西部TM图像逆冲断层解译及找煤研究

辽西坳陷中的断陷盆地边缘逆冲断层发育。本文描述了逆冲断层的TM影像特征,解译划分了逆冲断裂带,并指出逆冲断层对找煤远景解译推断的意义。具体分析了南票、北票矿区外围的找煤远景,还应用影像特征探索性地对逆冲断层倾角进行了解译分类。     

逆掩断层垂向封闭性定量模拟实验及评价方法

在正确分析逆掩断层形成的地质条件和封闭机理的基础上,本文认为与逆掩断层相伴生的塑性岩石的变形特征、断面压力和断裂带中泥质含量是影响断层垂向封闭性的主要因素。进行了断裂带填充物中泥质含量与断层封闭性定量关系物理模拟实验,并分析了岩石变形特征对断层封闭性的影响,建立了断层封闭性评价标准,提出了利用断裂带填充物质的性质、断面压力和膏泥岩变形特征评价断层封闭性方法。选择了库车坳陷克拉 3号构造进行了实例分析,结果表明该方法具有可靠性     

应用深部物探资料探讨赣中南地区深断裂、隐伏逆冲推覆构造与铀成矿的关系

通过对江西省１０条大地电磁测深（ＭＴ）剖面研究成果和区域重磁、莫霍面对比分析研究,讨论了赣中南地区深部地质构造格架。本区属华南块体。与扬子块体接壤地带的萍乡－广丰一线呈现为近东西向展布的幔凹－幔坡带。华南块体内部为北北东－北东向幔隆－幔坡－幔凹结构。莫霍面变异部位多为深断裂带反映。推断了近东西向展布的萍乡－广丰深断裂带、北北东向抚州－安远深断裂带和北北东向丰城－大余深断裂带;同时推断了北东向于都－宁都逆冲推覆滑覆构造系、近东西向乐安－南城逆冲推覆构造系等。根据铀矿产的分布,论证了莫霍面变异部位、逆冲推覆构造与铀成矿作用存在着十分密切的时空关系,为寻找隐伏铀矿提供了线索。     

地震叠前深度偏移方法流程及应用

针对复杂介质的成像问题，提出了一套地震资料叠前深度偏移方法流程，主要包括三部分：（１）地震资料精细预处理；（２）速度－深度模型建立；（３）叠前深度偏移成像．以Ｋｉｒｃｈｈｏｆｆ偏移理论为基础，强调地质与地球物理的综合以及地震处理与解释的一体化．在ＺＸ地区成功地实现了二维地震资料叠前深度偏移，所获得的ＮＥ２０６叠前深度偏移剖面揭示了复杂的ＺＸ古潜山及其内部构造，并清楚地展示了逆掩断层的存在．     

准噶尔盆地东北缘构造特征、演化及与油气的关系

通过“建造”与“改造”特征的综合分析，划分了准噶尔盆地东北缘的构造带：早古生代（1－2）陆缘逆冲带；晚古生代（D1）混杂岩浆碰撞带；晚古生代（D1）火山岩浆岛弧挤带；晚古生代（D2－3）弧后盆地褶皱带；晚古生代（C1－P2）陆缘盆地褶皱带以及中生代前陆盆地平缓背斜带等6个构造带。自古生代以来，曾发生了两次拉张－碰撞（闭合）－推覆的演化过程，均表现为“北挤南拉”和“北老南新”的构造迁移，直到二叠纪末期，相当于晚海西期构造运动，全区发生大规模褶皱变形和挤压推覆。最后依据构造特征和演分分析结果，笔建议在双井子级盆地褶皱带具备良好石油地质条件的有利油气区做进一步工作。     

西天山造山带的构造变形特征研究

西天山造山带由伊犁中天山北缘－北天山推覆走滑系统、伊犁中天山南缘－南天山推覆走滑系统和两者之间的伊犁地块组成。伊犁中天山北缘－北天山推覆走滑系统包括北天山推覆构造带、伊犁中天山北缘逆冲带和中天山北缘断裂带。伊犁中天山南缘－南天山推覆系统包括中天山南缘逆冲带、南天山北坡增生楔推覆席、南天山北坡早古生代被动陆缘推覆席、南天山南坡晚古生代洋壳－火山弧－复理石复合推覆席、中天山南缘断裂带和南天山南坡断裂带。区域构造和变形构造的研究表明西天山推覆构造主要奠定于早二叠世早期，走滑运动发生于晚二叠世－早三叠世。中新生代，沿古生代构造有进一步的推覆和走滑运动发生     

徐州吴桥—张圩地区新元古界地层特征与平衡地质剖面研究

徐州铜山吴桥—睢宁张圩一带主要出露一套新元古代地层 ,包括贾园组、赵圩组、倪园组和九顶山组 ,贾园组未见底、九顶山组未见顶。贾园组主要为灰色薄—中厚层细砂质、粉砂质泥质微晶灰岩 ,赵圩组主要为中厚层微晶灰岩 ,倪园组主要为薄层—中厚层微晶白云岩和灰岩 ,九顶山组主要为中厚层微晶白云岩。岩层受推覆构造运动影响强烈变形 ,褶皱和断裂构造发育 ,文中运用平衡地质剖面方法 ,对二朗山—宋湾剖面进行了平衡后得出该区造山运动缩短量为 3 .0 km ,缩短率为 15 %。