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首页> 外文学位 >Structural analysis of spectacular late Eocene soft-sediment deformation in the lower Spears Group, Sawtooth Mountains, western New Mexico.
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Structural analysis of spectacular late Eocene soft-sediment deformation in the lower Spears Group, Sawtooth Mountains, western New Mexico.

机译：新墨西哥州西部锯齿山下部矛群中壮观的晚始新世软沉积变形的结构分析。

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摘要

Spectacular soft-sediment deformation (?150-m thick) in the upper Eocene lower Spears Group is exposed along the northern periphery of the Mogollon Datil volcanic field (MDVF) in the Sawtooth, Datil, and Gallinas Mountains of western New Mexico. Despite detailed studies of the stratigraphy, geochronology, and geochemistry of volcanic and volcaniclastic rocks in the MDVF, no thorough structural analysis of widespread soft-sediment deformation has been undertaken. The present study exploits excellent exposures in the Sawtooth Mountains to reconstruct the late Eocene deformational history of the northern MDVF.;Four methods were used to analyze lower Spears Group deformation: (1) 1:6000 scale geologic mapping on enlarged 1:24,000 USGS topographic quadrangle base maps, (2) mapping fault and bedding traces on oblique photos of cliff exposures, (3) measuring and describing slip and separation indicators such as Riedel shears, fault-plane striations, drag folds, and displaced contacts, and (4) analyzing thin sections of cataclasite and undeformed rock samples.;A structural stack with five distinct levels is present throughout the study area. The lowest level exposed is the middle to late Eocene Baca Formation with gently east-dipping bedding. A detachment fault sub-parallel to underlying bedding is present in some locations at the upper Baca contact and in others less than five meters above a depositional contact. Above the Baca, the volcaniclastic unit of Largo Creek (VLC) of the lower Spears Group forms a sheet (0--150 m thickness) of variably contorted sandstones. In thicker sections, localized listric faults in lower exposures are truncated above by a zone of up to five gently- to moderately-dipping faults (15°--35°) bounding deformed VLC sandstones. The upper VLC contact is an extensive gently- to moderately- dipping (5°--30°) detachment fault with indicators suggesting the upper plate slipped east or southeast. Overlying Dog Springs Formation (lower Spears Group) debris-flow deposits are sub-horizontal and parallel to the subjacent detachment in western peaks but, in eastern peaks, steeply east-dipping (75°--85°) and east-facing strata form a hanging-wall ramp. South- and southwest-striking reverse-dextral(?) faults offset the stack down to the east.;Analyzing the structural stack and incorporating previous investigators' findings results in multiple spatial and temporal interpretations. The detachment fault separating the Dog Springs from underlying units formed during one or more mass movements, possibly landsliding or block spreading events. The upper plate translated east or southeast, presumably from a topographically high area west of the Hickman fault zone. The hanging-wall ramp is interpreted to have formed where the detachment cut up- section eastward across an inferred growth fold adjacent to that fault. The unusually thick nature of soft-sediment deformation and common granular fault zones lacking sharp slip surfaces is attributed to shear of saturated and poorly-consolidated VLC sandstones by a thick (~375 m minimum) rigid overriding plate that may have slipped multiple times, as suggested by grain-size reduction and multiple slip surfaces in the detachment core. In lower Spears Group exposures east of the study area, exotic non-volcanic blocks were likely derived from southern sources. Crosscutting relationships between faults provide a timeline of deformation events. Following deposition of the lower Spears from 37--40 Ma, localized slumping and thrusting formed listric faults in the VLC. One or more large blocks of Dog Springs deposits detached from a western source and moved eastward over VLC deposits. Reverse-dextral faults offset the detachment fault down to the east, probably during late-Laramide transpression, which ended approximately 36 Ma, providing a minimum age constraint on deformation in the Sawtooth Mountains.
机译：在新墨西哥州西部的锯齿山，达蒂尔山和加利纳斯山的Mogollon Datil火山场（MDVF）的北缘，上始新世的下矛族的壮观的软沉积变形（约150 m厚）暴露在外。尽管对MDVF中火山岩和火山碎屑岩的地层学，年代学和地球化学进行了详细的研究，但尚未对广泛的软沉积变形进行详尽的结构分析。本研究利用在锯齿山的极好的暴露来重建北部MDVF的始新世晚期变形历史。;四种方法被用来分析较低的矛群变形：（1）1：6000比例尺的地质地图，放大了1：24,000 USGS地形四边形底图；（2）在悬崖暴露的倾斜照片上绘制断层和层理痕迹；（3）测量和描述滑移和分离指标，例如Riedel剪，断层平面条纹，阻力褶皱和位移接触，以及（4）用于分析加长石和未变形岩石样品的薄片。在整个研究区域中，存在具有五个不同水平的结构叠层。暴露的最低层是始新世中晚期的巴卡组，地层东缓。在上Baca接触点的某些位置处存在次平行于下层顺层的脱离断层，而在沉积接触点以上不到五米的其他位置则存在。在Baca之上，较低的Spears组的Largo Creek（VLC）的火山碎屑岩单元形成了一块厚度为0--150 m的扭曲扭曲的砂岩。在较厚的部分中，较低暴露区域的局部李斯特断裂在上方被一个最多5个以变形VLC砂岩为界的轻度至中度倾斜断层（15°--35°）的区域截断。上层VLC接触是一个广泛的，轻度到中度倾斜（5°--30°）的脱离断层，指示物表明上板向东或向东滑动。上层狗泉组（下矛组）的泥石流沉积物是水平的，与西峰的下分离线平行，但在东峰，陡峭的东倾（75°--85°）和朝东的地层形式吊墙坡道。向南和西南向逆转的右旋（？）断层将烟囱向东偏移。;分析构造烟囱，并结合先前研究人员的发现，得出多种时空解释。分离断层将狗弹簧与一种或多种群众运动（可能发生的滑坡或块状蔓延事件）中形成的底层单元分开。上板块向东或向东南平移，大概是从希克曼断裂带以西的地形高处。悬挂壁的坡道被解释为已形成，在该断层处，该断层向东穿过与该断层相邻的推测的生长褶皱向东切开。软沉积物变形和缺乏陡峭滑动面的普通颗粒断层带异常厚的性质，是由于厚的（至少约375 m）刚性上覆板剪切了饱和的和固结力差的VLC砂岩而造成的，该板可能滑动了多次，如晶粒尺寸减小和分离芯中有多个滑动表面提示了这一点。在研究区以东的较低Spears Group暴露地区，外来非火山岩块很可能来自南部地区。断层之间的横切关系提供了变形事件的时间表。在37--40 Ma下矛的沉积之后，局部塌陷和逆冲作用在VLC中形成了李斯特断裂。一个或多个大块的Dog Springs矿床与西方资源分离，并在VLC矿床上向东移动。右旋断层可能将分离断层向东偏移，可能是在后期拉拉酰胺逆转过程中，该断层终止于约36 Ma，从而为锯齿山的变形提供了最小的年龄限制。

著录项

  • 作者

    Dobbins, Jeffrey W.;

  • 作者单位

    New Mexico Institute of Mining and Technology.;

  • 授予单位 New Mexico Institute of Mining and Technology.;
  • 学科 Geology.
  • 学位 M.S.
  • 年度 2016
  • 页码 70 p.
  • 总页数 70
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 文学理论;
  • 关键词

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