南沙地块内破裂不整合与碰撞不整合的构造分析

廷贾断裂以东的南沙地块与南海北部陆缘共轭,因此其构造过程研究对认识整个南海的构造演化具有重要意义.地震资料和区域构造背景分析揭示,破裂不整合面(BU)和碰撞不整合面(CU)是控制南沙地块内盆地演化的骨架界面;为了揭示南沙地块内的主要构造过程,本文利用地震剖面分析和数值模拟的方法,侧重对两个重要界面开展构造分析.结果显示...     

中天山北缘华力西期造山作用——变质岩锆石U-Pb年代学限定

笔者对中天山微陆块北缘托克逊干沟地区角闪岩相变质岩中的锆石进行了U-Pb年代学研究,结果证明变质沉积岩中的碎屑锆石记录了从太古宙至元古宙(3320～530 Ma)的源区岩浆热事件,变质火成岩中的岩浆锆石记录了新元古代晚期(550 Ma)的岩浆作用,而变质锆石记录了晚泥盆纪(385～360 Ma)的变质作用。这一定年结果表明,中天山微陆块北缘的造山作用很可能发生在华力西期,中天山微陆块形成于新元古代以前,但并没有经历前寒武纪变质作用,具有与塔里木克拉通明显不同的前寒武纪构造演化历史。因此,中天山微陆块很可能是一个独立的块体,并不支持其是从塔里木板块分离出来的观点。     

扬子地块北缘晚古生代-早中生代裂谷系统的分布及成因分析

晚二叠世长兴期-早三叠世印度期,在扬子地块的西北缘发育了一系列北西向展布的深水盆地区。根据成因分析证实,它们为伸展背景下形成的裂谷系统或者裂谷盆地群。平面上各裂谷盆地彼此近于平行,与北侧的南秦岭造山带在走向上呈正交和大角度斜交的排列,自西向东依次为开江-梁平裂谷、城口-鄂西裂谷和荆门-当阳裂谷。其中的开江-梁平裂谷东西两侧发现了巨大的天然气田而引起石油勘探家和地质学家的关注。本文对于这些控制油气资源储备的裂谷体系的分布和形成机制进行研究后,认为它们形成于南秦岭洋闭合时的碰撞作用,是南秦岭造山带和扬子地块拼合时同生的巨型"碰撞裂谷系统"。     

羌塘盆地基底地层及大地构造性质

根据不同学者在盆地基底地层中所得出的锆石同位素测年数据进行统计分析,结合前人对羌塘地区大地构造方面的研究成果得出:羌塘盆地中央隆起带出露的变质岩基底可能经历过泛非时期构造热事件的作用,羌塘块体在演化过程中受到了南部冈瓦纳大陆的影响,这对于了解本地区的大地构造背景以及对古特提斯缝合带的研究有所帮助.     

The structural evolution of the Asinara Island (NW Sardinia,Italy)

The metamorphic basement of the Asinara island represents a key area of the Sardinia Variscan segment, because it displays an almost complete cross-section through the inner part of the Sardinia Variscan belt, where different tectono-metamorphic complexes have been juxtaposed along narrow belts of high-strain concentration. Detailed field mapping coupled with preliminary studies on the structural and metamorphic features of this small island, allow to draw a better picture of the structural frame issued from the Variscan collision in the inner zone of the belt. Three deformation phases related to crustal thickening in a compressive and transpressive, partitioned tectonic regime, followed by a later phase of extensional deformation have been recognised. In spite of a general HT/LP metamorphic overprint, linked to the post-collisional deformation phases, a relic Barrovian zoneography is still detectable. The Barrovian assemblages are preto syn-kinematic with respect to the D2 deformation phase, and pre-date the third, contractional tectonic event.

The HT/LP assemblage indicates a static growth of weakly deformed by the last deformation events. The complex geometry of the fabric associated to the D2 and D3 deformation events suggests an heterogenous deformation history with a monoclinic geometry characterized by switching of the stretching lineation orientation and a contrasting sense of displacement, probably controlled by a northward partitioned pure shear.     

Late Cretaceous ophiolite obduction and Paleocene India-Asia collision in the westernmost Himalaya

Abstract

Collision of the Kohistan island arc with Asia at ~100 Ma resulted in N-S compression within the Neo-Tethys at a spreading center north of the Indo-Pakistani craton. Subsequent India-Asia convergence converted the Neo-Tethyan spreading center into a short-lived subduction zone. The hanging wall of the subduction zone became the Waziristan, Khost and Jalalabad igneous complexes. During the Santonian- Campanian (late Cretaceous), thrusting of the NW IndoPakistani craton beneath Albian oceanic crust and a Cenomanian volcano-sedimentary complex, generated an ophiolite-radiolarite belt. Ophiolite obduction resulted in tectonic loading and flexural subsidence of the NW Indian margin and sub-CCD deposition of shelf-derived olistostromes and turbidites in the foredeep. Campanian-Maastriehtian calci- clastic and siliciclastic sediment gravity flows derived from both margins filled the foredeep as a huge allochthon of Triassic-Jurassic rise and slope strata was thrust ahead of the ophiolites onto the Indo-Pakistani craton. Shallow to intermediate marine strata covered the foredeep during the late Maastrichtian. As ophiolite obduction neared completion during the Maastrichtian, the majority of India-Asia convergence was accommodated along the southern margin of Asia. During the Paleocene, India was thrust beneath a second allochthon that included open marine middle Maastrichtian colored mélange which represents the Asian Makran-Indus-Tsangpo accretionary prism. Latérites that formed on the eroded ophiolites and structurally higher colored mélange during the Paleocene wei’e unconformably overlapped by upper Paleocene and Middle Eocene shallow marine limestone and shale that delineate distinct episodes of Paleocene collisional and Early Eocene post-collisional deformation.     

Differential absorption measurements of mesospheric and lower thermospheric electron densities using the Buckland Park MF radar

The differential absorption experiment (DAE) was first proposed in the 1950s for the estimation of mesospheric and lower thermospheric electron density using MF/HF radars. The technique was used extensively until the late 1970s, when interest in the technique declined, due to experimental limitations and questions regarding the assumptions of the technique. This paper describes the application of the DAE within the online observations of the Buckland Park MF (BPMF) radar. The experimental limitations of the technique for the BPMF radar are discussed, with particular attention paid to effects of complex gain differences between receiving channels used to decompose the linearly received signals into circular components. Hourly and monthly averaged midday DAE electron densities are presented, revealing good agreement with IRI model estimates. Monthly averaged midnight DAE electron densities are also presented, revealing good qualitative agreement with the IRI model estimates.     

北山泥盆纪碰撞造山火山－磨拉石地质构造及地球化学特征

本区早泥盆世旱山微大陆与塔里木板块的北山地体间发生对接，原洋区变为残留滨浅海区。中泥盆世该区形成中央断块山，相应南带的断陷山间洼地内形成陆相磨拉石堆积，北带与南蒙古洋毗邻，形成陆缘滨浅海火山－磨拉石沉积。经计算，中带造山隆起侵蚀速率为０．１５４ｍｍ／ａ。晚泥盆世火山岩显示弱碱性和深熔岩浆喷溢特点，表明陆壳演化尚未达到完全稳定的阶段。     

再论华南（东）晋宁－加里东海盆地形成、演化及封闭

华南（东）晋宁－加里东海盆地形成于青白口纪，经历了晋宁期，加里东早期及加里东晚期３个演化阶段。海盆地基底为陆壳，形成于拉伸的裂谷环境，海盆地的封闭以陆内俯冲及拼贴为主，具多阶段性。海盆地基底，特别是华夏地块基底高热值属性导致了加里东海盆地有湘桂海盆地和赣闽粤海盆地２种类型，后者位于华夏基底之上，活动性明显，形成数条陆内动力热流变质带。     

Regional Tectonic Transformation in East Kunlun Orogenic Belt in Early Paleozoic: Constraints from the Geochronology and Geochemistry of Helegangnaren Alkali-feldspar Granite

The Helegangnaren feldspar granite exposed in the eastern part of East Kunlun, is characterized by high concentrations of SiO2 and alkaline, low abundances of Fe, Mg and Ca, metaluminous-weak peraluminous. Trace elements analysis shows that the granite is depleted extremely in Ba, Sr and Eu, and rich in some large-ion lithophile elements and high field strength elements. Besides, the granite has high Ga contents, the values of 104(Ga/Al) vary from 2.50 to 2.77, which is mainly greater than the lower limit of A-type granites (2.6), and is higher than the I- and S-type granites’ average (2.1 and 2.28, respectively). Rare earth element (REE) is characterized by relatively high fractionations of light REE (LREE) and heavy REE (HREE) (LREE/HREE=9.3–13.60, (La/Yb)N=10.92–18.02), pronounced negative Eu anomalies (δEu=0.08–0.13), and exhibits right-dipping gull pattern. Major elements, rare elements and trace elements features show the granite is ascribed to A-type granite and A2 subtype in tectonic genetic type. They are plotted into post-collision or within-plate area in a variety of tectonic discriminations. Geological and geochemical data comprehensively suggest that the granite is formed in a post-collision extensive tectonic setting. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields a weighted mean age of 425?Ma, belonging to Middle Silurian, which is similar to the age of the post-collision geological events in the region. The differences of magmatic rocks in formation age, rocks assemblage and rocks series systematically indicate that the regional tectonic stress regime in the East Kunlun orogenic belt experienced a major transformation from compress to extension in Middle Silurianin, and the Helegangnaren feldspar granite intruded in the early stage of tectonic transformation.