Intrusion age, geochemistry and metamorphic conditions of a quartz-monzosyenite intrusion at the craton–Eastern Ghats Belt contact near Jojuru, India     

D. Upadhyay  M.M. Raith 《Gondwana Research》2006,10(3-4):267-276

The boundary between the Archean cratons and the Eastern Ghats Belt in peninsular India represents a rifted Mesoproterozoic continental margin which was overprinted by a Pan-African collisional event associated with the westward thrusting of the Eastern Ghats granulites over the cratonic foreland. The contact zone contains a number of deformed and metamorphosed nepheline syenite complexes of rift-related geochemical affinities. In addition to the nepheline-bearing rocks, metamorphosed quartz-bearing monzosyenitic bodies can also be identified along the suture in the region between the Godavari-Pranhita graben and the Prakasam Igneous Province. One such occurrence at Jojuru near Kondapalle is geochemically comparable to the nepheline syenites and furnishes a weighted mean concordant U–Th–Pb SHRIMP zircon age of 1263 ± 23 Ma (2σ), which provides a lower age bracket for the rift-related magmatic activity. The original igneous mineral assemblage in the monzosyenite was partially replaced by the formation of coronitic garnet during the Pan-African metamorphism of the rocks. P–T estimates of garnet corona formation at the interface between clinopyroxene–orthopyroxene–ilmenite clusters and plagioclase indicate mid to upper amphibolite facies condition (5.5–7.0 kbar and 600–700 °C) during the thrust induced deformation and metamorphism associated with the Pan-African collisional tectonics.  相似文献   

河北省赤城县温泉环斑花岗岩的地质特征及形成时代   总被引：2，自引：0，他引：2       下载免费PDF全文

刘振锋  王继明吕金波郑桂森 《中国地质》2006,33(5):1052-1058

温泉环斑花岗岩分布于河北省赤城县温泉一带,面积约50km2。在1:25万延庆县幅区域地质调查工作的基础上,笔者研究了该岩体的产出状况、侵入关系等地质特征。结合岩石学、地球化学及同位素年龄等证据,探讨了温泉环斑花岗岩的形成时代。研究表明,该岩体为富钾、过铝、高铁、低钙、低镁A型花岗岩,形成于中元古代,相当于长城纪大红峪期,与北京市密云县沙厂环斑花岗岩可以对比。同时也为华北板块基底的克拉通化时间及其在中元古代发生的裂解事件提供了岩石学及同位素年龄依据。  相似文献   

华北中部古元古代末期构造－热事件性质及其构造成因模式   总被引：2，自引：1，他引：2       下载免费PDF全文

李江海刘守偈  侯贵廷 《中国地质》2006,33(6):1256-1266

古元古代末期为华北克拉通演化的重大转折时期。但这一时期重大构造热事件序列及其构造格局的研究较薄弱。笔者在区域构造分析基础上。结合最新的同位素年龄制约。探讨古元古代末期区域构造演化过程及其成因模式。太行山-恒山基性岩墙群对应于燕辽坳拉谷与太行坳拉谷的夭折支，它们共同构成非对称的三叉坳拉谷系。非造山的岩浆活动序次依次为：花岗岩、伟晶岩（1．85～1．80Ga）、基性岩墙群侵位（1．80-1．77Ga）、斜长岩、碱性花岗岩、环斑花岗岩（1．71-1．70Ga）、火山岩喷发（1．68Ga）等。下伏基底性质对比及其同位素年龄表明，18亿年前后燕辽-太行山地区发生大规模隆升。隆升范围达上千千米，核心区处于燕辽-太行山坳拉谷系中心位置。基底隆升事件与浅表层伸展构造-非造山岩浆活动在时空上相吻合，表明地幔柱模式可以合理解释上述区域隆升及其伸展裂解事件。  相似文献   

Origin of Molar-Tooth Structure Based on Sequence- Stratigraphic Position and Macroscopic Features： Example from Mesoproterozoic Gaoyuzhuang Formation at Jixian Section, Tianjin, North China   总被引：2，自引：1，他引：2  

梅冥相 《中国地质大学学报(英文版)》2006,17(3):201-208,271

INTRODUCTION Located at the famous Jixian Section in Tianjinin the North China , the MesoproterozoicGaoyuzhuang Formationis a set of 1 600 mthick car-bonates that formed over about 200 Ma in the Clym-Figure 1 .Section location of the Mesoprotero-zoic Gaoyuzhuang Formation at the Jixian Sec-tion in Tianjin.mian (1 600 Ma to 1 400 Ma ;Zhu et al .,1994 ; Du,1992 ;Fig.1) . The Gaoyuzhuang Formation at theJixian Section can be divided into four members thatare characterized by differ…  相似文献   

赣东北万年地区万年群的建立及其意义   总被引：6，自引：0，他引：6  

吴新华  楼法生  刘春根  赵炼忠 《地质通报》2005,24(9):819-825

万年群是发育在江南复合混杂岩带中之赣东北进贤——万年地区的一套中元古代蓟县纪浅变质岩系。据其岩性组合、沉积环境等特征自下而上进一步划分为枫树岭组、牛头岭组、皮库组和程源组，岩石地球化学特征反映其大地构造环境为大陆岛弧——弧后盆地，其层位与弧后盆地之双桥山群安乐林组、修水组，溪口岩群，火山岛弧的双溪坞群和弧间盆地的张村群相当。但岩性组合差异甚大，属同时异相的产物。万年群的建立为华南中元古代地层的划分对比提供了新的思路。  相似文献   

天津蓟县中元古界高于庄组“球形臼齿状构造”新解——1400 Ma以前球形或似球形实体宏观藻类化石的细胞显微结构   总被引：1，自引：0，他引：1  

梅冥相 《现代地质》2007,21(4):738-748

天津蓟县剖面高于庄组,组成一个复杂而特别的叠层石—非叠层石碳酸盐岩沉积序列,其中,第三段构成一个特征迥异的非叠层石碳酸盐岩沉积序列。在该非叠层石序列上部的均一石灰岩(隐晶质泥晶灰岩)中普遍发育大小不等的带状臼齿状构造,与臼齿状构造共同产出的是一些数毫米乃至厘米级的球形体或似球形体。这些球形体或似球形体,曾经被解释为球形臼齿状构造,也被解释为灰岩结核、燧石结核或凝灰岩结核。岩石薄片的显微镜观察表明,这些球形体或似球形体的内部,显示出较为明显但又较为原始的多细胞组织,如分生组织和类似于薄壁组织的成熟组织,其中一些成熟细胞还保留着较为明显的细胞显微结构,表明这些球形体或似球形体的内部结构明显不同于臼齿状构造的特殊填充物——等粒状微亮晶方解石。因此,这些球形体或似球形体应该归为丘尔藻或拟丘尔藻之类的宏观藻类化石,而不是球形臼齿状构造。尽管前人在前寒武纪地层之中描述了若干宏观藻类化石,但多以碳质压型的形式保存在泥岩之类的细粒沉积之中。发现于天津蓟县剖面高于庄组灰岩中的实体球形或似球形宏观藻类化石,以其较老的地质年代(大于1400Ma)、较为明显而又原始的多细胞组织和一些成熟细胞的可能细胞显微结构,表明该球形实体化石具明显的多细胞真核生物属性。这些初步研究和发现为探讨真核生物的起源演变、揭示宏观藻类化石的生物学属性提供了罕见的实际材料,因而具有重要的意义。  相似文献   

Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China: A Case Study of the Langshan-Zha'ertaishan Belt,Inner Mongolia, China     

PENG Runmin  ZHAI YushengKey Laboratory of Lithospheric Tectonics  Lithoprobing Technology  China University of Geosciences  Ministry of Education  Beijing 《《地质学报》英文版》2004,78(2)

Most ore-forming characteristics of the Langshan-Zha'ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha'ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures, showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical  相似文献   

The paleomagnetism and geological significance of Mesoproterozoic dyke swarms in the central North China Craton   总被引：4，自引：0，他引：4  

HOU Guiting  LI Jianghai  QIAN Xianglin  ZHANG Baoxing  H.C.Halls 《中国科学D辑(英文版)》2001,44(2):185-192

The Mesoproterozoic mafic dyke swarms are extensively distributed in the central North China Craton(NCC) including North Shanxi, Wutai and Lüliang areas, which are not deformed and metamorphic but high magnetic, so the dyke swarms become the mark to compare the high metamorphic rock areas in magnetism. Based on the analysis of paleomagnetism of mafic dyke swarms in North Shanxi, Wutai and Lüliang areas, NCC inclined southward about 18ü so that North Shanxi lifted up and rotated 10ü left to Wutai area. The dyke swarms in Lüliang developed later than in North Shanxi and Wutai area. The NNW-trending and WNW-trending dyke swarms developed in Lüliang while the North China Plate moved northward consistently so that the paleomagnetism of dyke swarms in Lüliang is greatly different from North Shanxi and Wutai area.  相似文献   

Earthquake event deposits in Mesoproterozoic Kunyang Group in central Yunnan Province and its geological implications   总被引：4，自引：0，他引：4  

Du Yuansheng  ZHANG Chuanheng  HAN Xin  GU Songzhu  Lin Wenjiao 《中国科学D辑(英文版)》2001,44(7):600-608

Earthquake and its resultant tsunami, as a kind of disaster events in geological history, may be recorded as event deposits of seismite and tsunamite. Typical characteristics of seismite and tsunamite, including seismo-fracture bed, synsedimentary microfracture, micro-corrugated lamination, molar tooth structure, hummocky bedding, occurs in Mesoproterozoic Dalongkou Formation of Kunyang Group in central Yunnan Province. Three types of sedimentary units have been recognized: seismite (unit-A, including limestone with molar tooth structure, seismic shattering rock, seismic corrugated rock, autoclastic breccia and intraclastic parabreccia), tsunamite (unit-B, intraclastic limestone with hummocky or parallel beddings) and background deposits (unit-C). Various stackings of these units construct three distinct sedimentary sequences: A-B-C, A-C and B-C. A-B-C represents an event sedimentary sequence of earthquake-tsunami-background deposits, A-C represents the sequence of earthquake and background deposits (no tsunami occurring), and B-C represents the sequence of tsunami and background deposits (far from the center of earthquake). As the central Yunnan Province was located in a tectonic setting of rift basin in Mesoproterozoic Era, the earthquake event deposits of the Dalongkou Formation are sedimentary response to tectonic activity of the rift basin.  相似文献   

华北燕山地区中新元古代沉积记录及其古气候、古环境特征   总被引：10，自引：0，他引：10  

吉利明  陈践发  郑建京  王杰 《地球科学进展》2001,16(6):777-784

大量研究表明大约 1．0～0．8GaBP时期，全球形成统一的Rodinia超大陆，当时华北地块处于中低纬度地区，与劳伦及西伯利亚地块相连。燕山地区的中上元古界是以大套碳酸盐建造为主的结晶基底之上的第一盖层沉积。元古代地球大气-海洋系统发生了 O₂增多、CO₂减少的古全球变化，1．85GaBP开始由还原性转变为氧化性，随着条带状硅铁沉积在全球的终止，出现广泛的红土堆积。甾烷、藿烷及类异戊二烯等生物标志物在前寒武纪沉积中的大量检出，表明早在古元古代地球上就可能已经有真核生物、真菌及光合细菌存在。近年来燕山中元古界长城系、蓟县系发现大量地球早期生物化石，包括真核藻类、多细胞藻类、颗石藻、藻叠层石及后生动物遗迹等，对探讨各种生命形式的起源与演化、恢复古环境与古气候变化过程都具有重要的意义。  相似文献