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91.
92.
郯庐断裂带张八岭隆起北段的左旋走滑挤压变形及其~(40)Ar/~(39)Ar定年 总被引:4,自引:0,他引:4
郯庐断裂带张八岭隆起北段,自西向东分别出露北北东向的韧性滑脱变形带、脆-韧性过渡带和脆性的前陆褶断带。韧性滑脱变形带内的张八岭群片岩,广泛发生了低绿片相背景下的糜棱岩化。其中呈现为平缓的糜棱面理和近南北向的矿物拉伸线理。显微构造及石英C轴组构分析显示,该韧性滑脱带一致为上盘向南的运动。该带以东依次变为上盘向南南东→南东的逆冲活动,总体上为左旋走滑挤压变形带。张八岭群所在的韧性变形带为深部陡立走滑构造与浅部脆性构造之间的滑脱变形带,其间的差异走滑变形,造成了该滑脱层在总体向北运动中出现上盘向南的剪切变形。对6处张八岭群片岩中15个不同粒级白云母的40Ar/39Ar定年指示,变形发生在(236.2±0.5)~(238.0±0.4)Ma的中三叠世晚期。这表明郯庐断裂带的左行平移发生在华北与华南板块碰撞的深俯冲阶段,起源于陆内转换断层。 相似文献
93.
S.I. Sherman E.A.Gorbunova 《地学前缘》2008,15(3):337-347
已有的地质和地球物理方法无法对年、月、旬等现今时间尺度上的断层活动变化进行有效预测。运用基于地震活动定量指数运算程序的地理信息技术可以解决这个问题。这种方法被应用于贝加尔裂谷系(BRS)及邻区的研究当中。研究发现,断层活动变化发生在以几年为周期的时间尺度上,这无法用区域应力场的变化进行合理解释。沿着穿越贝加尔裂谷系的剖面编制了活动断层图以及地震活动定量指数曲线。提出的这种方法可以根据地震活动定量指数对活动断层进行仔细的分类,从而为解决地震中期预报相关问题开辟了重要途径。这种方法还被用来研究断层现今活动的时空变化和形成机制。研究发现,在实时尺度上断层活动具有高频发生的特征,这种现象可能是由于脆性岩石圈板内和块体内部运动产生的慢变形波的干扰导致的。利用变形波的通过速度可以对活动断层进行分组,各组具有不同的地质和地球物理特征参数,同时还可以对变形波波前的方向以及某一区域内主要断层在实时间隔内(地质上的瞬间)的活动情况进行预测。 相似文献
94.
95.
96.
浑河断裂带(抚顺段)近期活动性与地质灾害的关系 总被引:1,自引:0,他引:1
通过对浑河断裂带(抚顺段)的地质调查、人工地震勘查、断裂绝对年龄测定、跨断裂形变测量等资料的综合分析与研究,讨论了断裂构造的近期活动特征,并据此认为浑河断裂自晚更新世以来若非人类工程活动扰动是没有活动的,现今的断裂活化效应是由于大量的人类采煤活动造成的。由于断裂的活化效应破坏了抚顺煤田及其周围区域原始构造应力场的平衡状态,为达到新的平衡必然导致应力的重新集中与释放,在此过程中伴随产生了抚顺煤田广泛发育的滑坡、地面沉陷、矿震、地裂缝等地质灾害。 相似文献
97.
We simulate direct current (DC) borehole resistivity measurements acquired in steel-cased deviated wells for the assessment
of rock formation properties. The assumed data acquisition configuration considers one current (emitter) and three voltage
(collector) electrodes that are utilized to measure the second difference of the electric potential along the well trajectory.
We assume a homogeneous, 1.27-cm-thick steel casing with resistivity equal to 10 − 5 Ω· m. Simulations are performed with two different numerical methodologies. The first one is based on transferring two-dimensional
(2D) axisymmetric optimal grids to a three-dimensional (3D) simulation software. The second one automatically produces optimal
3D grids yielded by a 3D self-adaptive goal-oriented algorithm. Both methodologies utilize high-order finite elements (FE)
that are specially well-suited for problems with high-contrast coefficients and rapid spatial variations of the electric field,
as it occurs in simulations that involve steel-cased wells. The method based on transferring 2D-optimal grids is efficient
in terms of CPU time (few seconds per logging position). Unfortunately, it may produce inaccurate 3D simulations in deviated
wells, even though the error remains below 1% for the axisymmetric (vertical) well. The method based on optimal 3D grids,
although less efficient in terms of CPU time (few hours per logging position), produces more accurate results that are validated
by a built-in a posteriori error estimator. This paper provides the first existing simulations of through-casing resistivity
measurements in deviated wells. Simulated resistivity measurements indicate that, for a 30° deviated well, measurements in
conductive layers 0.01 Ω· m) are similar to those obtained in vertical wells. However, in resistive layers (10,000 Ω· m),
we observe 100% larger readings in the 30° deviated well. This difference becomes 3,000% for the case of a 60° deviated well.
For this highly-deviated well, readings corresponding to the conductive formation layer are about 30% smaller in magnitude
than those in a vertical well. Shoulder effects significantly vary in deviated wells. 相似文献
98.
In this paper, we formulate a finite-element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation
model of poroelasticity. We approximate the flow variables by a mixed finite-element space and the displacement by a family
of discontinuous Galerkin methods. Theoretical convergence error estimates are derived and, in particular, are shown to be
independent of the constrained specific storage coefficient, c
o
. This suggests that our proposed algorithm is a potentially effective way to combat locking, or the nonphysical pressure
oscillations, which sometimes arise in numerical algorithms for poroelasticity. 相似文献
99.
O. Maurel P. Moniè R. Pik N. Arnaud M. Brunel M. Jolivet 《International Journal of Earth Sciences》2008,97(3):565-584
Vertical displacements on the SW–NE Têt fault (Eastern Pyrenees Axial Zone, France), which separates the Variscan Canigou-Carança and Mont-Louis massifs, were constrained using a thermochronologic multi-method approach. 40Ar/39Ar data from the granitic Mont-Louis massif record its Variscan cooling history and reveal no ages younger than Early Cretaceous, while the Canigou-Carança gneiss massif records systematically younger 40Ar/39Ar ages. These younger 40Ar/39Ar ages in the Canigou-Carança gneiss massif are the result of partial to total rejuvenation of argon isotopic systems related to a thermal flow coeval with the Cretaceous HT-BP metamorphism in the North Pyrenean Zone. Only the deepest rocks from the Canigou-Carança suffered this extensive Mid-Cretaceous thermal overprint probably due to differential burial around 4 km at that time. The post Mid-Cretaceous vertical displacements along the Têt fault are recorded by “low” temperature thermochronology using K-feldspar 40Ar/39Ar, zircon and apatite fission track and (U–Th)/He datings. The Mont-Louis granite samples experienced a long period of protracted cooling reflecting a lack of thermo-tectonic activity in this area from Late Palaeozoic to Early Cenozoic, followed by cooling from 55–60 Ma to Late Eocene at a mean rate of 15–20°C/Ma in the final stage. This cooling stage corresponds to Têt fault reactivation with a reversed component, promoting exhumation of the Mont-Louis roof zone contemporaneously with the south-vergent Pyrenean thrusting. In the Canigou-Carança massif, the main cooling event occurred from 32 to 18 Ma at a maximum rate of 30°C/Ma during Early Oligocene followed by a more moderate rate of 3°C/Ma from Late Oligocene to Early Burdigalian, coeval with the normal reactivation of the Têt fault in brittle conditions that accommodated the final exhumation of the massif during the opening of the Gulf of Lion. 相似文献
100.
Makoto Yamano Masataka Kinoshita Shusaku Goto 《International Journal of Earth Sciences》2008,97(2):345-352
Thirty-three new measurements on the seaward slope and outer rise of the Japan Trench along a parallel of 38°45′N revealed
the existence of high heat flow anomalies on the subducting Pacific plate, where the seafloor age is about 135 m.y.. The most
prominent anomaly with the highest value of 114 mW/m2 is associated with a small mound on the outer rise, which was reported to be a kind of mud volcano. On the seaward slope
of the trench, heat flow is variable: high (70–90 mW/m2) at some locations and normal for the seafloor age (about 50 mW/m2) at others. The spatial variation of heat flow may be related to development of normal faults and horst/graben structures
due to bending of the Pacific plate before subduction, with fluid flow along the fault zones enhancing the vertical heat transfer.
Possible heat sources of the high heat flow anomalies are intra-plate volcanism in the last several million years like that
discovered recently on the Pacific plate east of the Japan Trench. 相似文献