Tectonometamorphic Cycles in Different Geodynamic Conditions

ＩＮＴＲＯＤＵＣＴＩＯＮＳｙｓｔｅｍａｔｉｚａｔｉｏｎｏｆｋｎｏｗｌｅｄｇｅｏｆｓｐａｔｉａｌａｎｄｔｅｍｐｏｒａｌｒｅｌａ ｔｉｏｎｓｂｅｔｗｅｅｎｒｅｇｉｏｎａｌｍｅｔａｍｏｒｐｈｉｓｍａｎｄｄｅｆｏｒｍａｔｉｏｎｓｒｅｓｕｌｔ ｅｄ ,ａｔｔｈｅｂｅｇｉｎｎｉｎｇｏｆ 1970ｓ,ｉｎｄｉｓｔｉｎｃｔｉｏｎｏｆｔｅｃｔｏｎｏｍｅｔａ ｍｏｒｐｈｉｃｃｙｃｌｅｓ (ＴＭＣ)ｗｈｉｃｈｒｅｆｌｅｃｔｏｎｅ ａｃｔｍａｎｉｆｅｓｔａｔｉｏｎｏｆｍｅｔａｍｏｒｐｈｉｓｍａｎｄａｃｃｏｍｐａｎｙｉｎｇｅｎｄｏｇｅ…     

青藏高原东北缘推覆体构造稳定性定量化评价——以龙门山推覆体为例

2008年5月12日汶川特大地震震害调查及分析表明,目前以活动断裂和历史地震调查为重点的工程区域构造稳定性评价方法存在漏判与误判特大地震问题,从而为工程安全埋下重大安全隐患。以龙门山活动推覆体为例,在已有研究成果基础上,利用岩体结构控制论、拜尔利定律等普适性原理对龙门山地壳岩体结构力学特征、控震结构面的抗剪强度与地震震级的线性相关性、地震震级与抗震设防烈度的关系进行了定量研究,对评价区域构造稳定性的关键问题进行了探讨。结果表明,推覆体型活动地块边界带中的滑脱层是对推覆体区域构造稳定性起主要控制作用的构造结构面--控震结构面,地震震级与滑脱层的埋深、抗剪切强度存在显著相关性：8级地震的震源深度接近20 km、7级地震的震源深度接近14 km、6级地震的震源深度接近10 km,据此对研究区及邻近的古地震进行了深度核定,圈定了龙门山活动推覆体-岷山地块的6级以上强震可能发生的范围、对应Ⅶ－Ⅺ度的抗震设防烈度范围。此研究成果弥补了以往根据活动断裂-发震断裂-历史最大震级与对应地震烈度评价工程区域构造稳定性,因历史地震资料疏漏不全、活动断裂带研究平面与深度范围局限以及忽视区域构造稳定性的岩体力学实质而导致评价结果常常出现误判与漏判的诸多缺陷。     

The origin of the 2008 Wenchuan Earthquake determined by the analysis on the active Longmenshan nappe in terms of rockmass mechanics

On 12 May 2008, the magnitude 8.0 Wenchuan Earthquake occurred along the Longmen Shan nappe, Sichuan, China. This devastating earthquake led to a heavy death toll of greater than 80,000. The seismic origin of this earthquake is currently hotly debated. We suppose that it is a special type of intraplate earthquake called an active-nappe-type earthquake. Using a holistic methodology, incorporating rockmass structure cybernetics and Byerlee’s law, we present a comprehensive study on the geological origin of macroseisms in the Longmen Shan area and the seismic origin of the 2008 Wenchuan earthquake. Previous studies of neotectonic activity indicate that the Longmen Shan nappe moves at a rate of 1~3 mm/yr, due to horizontal compressive stress from the Tibetan Plateau. The difference between movement rates in the Bayankala block, Longmen Shan nappe and Sichuan Basin cause slow shear stress and strain accumulation in the Longmen Shan nappe. It is exhibited a relatively simple linear relations for the shear strength and the buried depth of the structural planes, and the detachment layer of the nappe has a higher shearing-sliding strength compared to the overlying fault planes and the underlying ductile shear belts, thus making it more prone to stick-slip deformation. Therefore, the detachment layer was the main section responsible for the Wenchuan earthquake. The initial rupture burst in the detachment layer under the Yingxiu-Beichuan fault, the rupture area nearly 1.4454 × 104 km2,encompassed the cross point of the Yingxiu and the Anxian-Guanxian faults with the detachment layer, then caused the Yingxiu-Beichuan and Anxian-Guanxian faults took an active part in this earthquake, so this earthquake might consist of three chain-like earthquake stages, totally increasing the duration of this earthquake an unusually large amount, to 120 s. The focal depth spanned range of 10-20km,consistent with the observed result of this focal depth by several agencies.     

滇西北剑川-虎跳峡大规模东向西逆冲推覆构造——兼论滇西扬子陆块区与西藏-三江造山系界线

基于剑川至虎跳峡一带的野外区域地质调查资料, 论述剑川-虎跳峡断裂的性质, 进而探讨扬子-华南陆块区与西藏-三江造山系的界线。野外观察显示, 该区存在大规模自东向西的逆冲推覆构造, 从剑川开始, 经丽江白汉场—汝寒坪、忠义村, 至香格里拉县的虎跳峡镇(下桥头)等地, 多条剖面可见上扬子稳定型的古生代及中生代三叠纪地层自东向西逆冲推覆在西藏-三江造山系地层层序之上, 推覆距离大于50 km。因此, 剑川—虎跳峡断裂不是两大板块的边界, 而是一条狭长的构造窗。两大板块的界线应是大理-剑川-丽江-木里断裂, 南段接红河断裂。      

辽宁建平黄花山金矿床地质特征及成矿模式

黄花山金矿系辽西建平地区重要的热液蚀变岩型金矿.新太古代变质基底片麻岩系为金矿的矿源层,中元古代侵入岩为金矿的主要容矿围岩,晚侏罗世侵入岩是金矿的成矿岩体.黄花山地区在印支期形成了北西向南东推覆的叠瓦状逆冲推覆构造,并长期活动,为成矿提供了空间.由于燕山期岩浆活动剧烈,即侵入体同下伏古老地层中金矿源层的重熔或捕获古老含金丰度高的层位,这些成矿热液沿黄花山叠瓦状逆冲推覆构造上升,并在逆冲推覆构造带中堆积形成了金矿体.通过总结、分析成矿的主要过程,建立了黄花山金矿的成矿模式.     

The Rand Granite in the southern Schwarzwald and its geodynamic significance in the Variscan belt of SW Germany

The Rand Granite is a heterogeneous metamorphosed granitoid rock complex with numerous wallrock inclusions situated in the Moldanubian Zone at the southern margin of the Central Schwarzwald Gneiss Complex. It is a largely mylonitized elongated body and is thrust over the Badenweiler-Lenzkirch Zone forming a nappe with shear zones along its northern and southern boundaries. It comprises meta-granites, meta-trondhjemites and biotite augen gneisses derived from monzogranites to granodiorites. Mineral behaviour indicates that the magmatic body has been deformed under upper greenschist facies conditions. Nappe thrusting, which also affected the South Schwarzwald Gneiss Complex, occurred in Visean time during high-temperature / low-pressure metamorphism. Kinematic indicators in the mylonites document E- to ESE-directed nappe transport, highly transpressive relative to the trend of the nappe boundaries and the foliation. The trondhjemites formed at 351 +5/-4 Ma, predating the Variscan HT metamorphism. They have initial _Nd-values of +6.6 to +6.7 and relatively low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7042 to 0.7063), indicating a predominant mantle origin. The granites and protoliths of the biotite augen gneisses probably crystallised between 436 and 377 Ma, suggested by U-Pb zircon model ages. They are different from the trondhjemites with low initial _Nd-values (–4.7 to –3.3) and higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7068–0.7077), indicating that large part of the Rand Granite originated from anatexis of continental crust. Internal structure of zircons from the Rand Granite reveals mixing of magmas derived from both mantle and crust sources. These new data support an interpretation that the Rand Granite developed along an active continental margin and therefore represents a possible root of a Variscan magmatic arc.     

西准噶尔达拉布特断裂系构造演化特征

呈北东走向横贯于西准噶尔的达拉布特断裂系,是一组倾向北西的犁状断层。断裂系的形成、发育是由于碰撞后的西伯利亚、哈萨克斯坦和塔里木三大陆块在早石炭世以后,仍在不断地相向运动。由此所形成的断裂系,其早期是以左行陡倾的走滑断层形式出现;中期受陆内俯冲作用的影响,被强烈的推覆构造改造成上陡下缓的犁状断层;娩近时期,断裂处于引张状态,表现为正断层性质,形成了明显的断层地貌。     

黄陇侏罗纪煤田陇县地区构造及控煤作用分析

研究区位于陇东黄土高原区,大部分地方为Q2＋3黄土所覆盖,煤系地层的构造形态及煤层的赋存状况无法从地表直接获得.从构造演化的角度,结合地层沉积建造,通过构造控煤作用分析,总结了区内煤系的发育特征和赋存规律.     

燕山造山带复杂构造变形型式的新证据及其地质意义

我们在燕山造山带若干区域的构造填图工作表明，燕山带构造变形型式十分复杂。在华北地区中元古代“标准剖面”所在的天津市蓟县常州村-团山子-杨庄地区，我们的填图工作识别出众多的逆冲构造。在北京市东部密云县丰台顶一带发现了褶皱的推覆体。在北京市西北部延庆县的河口．石槽地区填绘出强烈变形的褶皱冲断构造。但是，前人已发表的地质图并未显示这些构造形迹。根据G A Davis及其合作者的研究和我们的调查工作，我们认为前人对燕山造山带的填图工作在识别区域主要构造特征方面是不成功的，燕山带挤压变形比前人所认为的要更为强烈和复杂。