Extensional tectonic origin of gneissosity and related structures of the Feiran–Solaf metamorphic belt, Sinai, Egypt     

A. Fowler  I. Hassan 《Precambrian Research》2008,164(3-4):119-136

The Feiran–Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S₁, and is almost everywhere parallel to lithological layering, S₀. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S₀. S₁ formed by coaxial pure shear flattening strain (Z normal to S₀, i.e. vertical; with X and Y both extensional and lying in S₁). This strain also produced chocolate tablet boudinage of some layers and S₁-concordant sills and veins. S₁ has a strong stretching lineation L₁ with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L₁-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F₁ folds with hinges parallel to the stretching lineation. F₁ fold asymmetry variations do not support previous models involving macroscopic F₁ folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran–Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia.  相似文献   

The Migif–Hafafit gneissic complex of the Egyptian Eastern Desert: fold interference patterns involving multiply deformed sheath folds     

Abdel-Rahman Fowler  Baher El Kalioubi 《Tectonophysics》2002,346(3-4)

The Wadi Hafafit Complex (WHC) is an arcuate belt of orthogneisses, migmatites and other high-grade metamorphic rocks, which marks the boundary between the Central Eastern and the South Eastern Deserts of Egypt. In the WHC, gneissic meta-gabbro outlines macroscopic fold interference patterns characterized by elliptical to irregular culminations cored by gneissic meta-tonalite to meta-trondhjemite. The five main culminations of the WHC have previously been labeled A (most northerly), B, C, D and E (most southerly). A detailed structural investigation of B, C, D and E reveals that these structures are a result of the interference of four macroscopic fold phases, the first three of which may represent a single deformation event. The first folding involved sheath-like fold nappes, which were transported to the N or NW, assisted by translation on gently dipping mylonite zones. The regional gneissosity and mineral extension lineations formed during this folding event. The fold nappes were deformed by mainly open upright small macroscopic and mesocopic folds with approximately NE-trending hinges. As a probable continuation of the latter folding, the sheaths were buckled into large macroscopic folds and monoclines with the same NE-trends. The fourth macroscopic folding resulted from shortening along the NE–SW direction, producing mainly NW–SE-trending upright gently plunging folds. Gravitative uplift is disputed as a component of the deformation history of the WHC. The peculiarities of the fold interference pattern result from the interesting behaviour of sheath folds during their refolding.  相似文献   

新疆西南天山木扎尔特一带低压麻粒岩相变质作用P-T轨迹及其地质意义   总被引：11，自引：5，他引：11  

李强  张立飞 《岩石学报》2004,20(3):583-594

本文首次报道在新疆西南天山木扎尔特一带发现了二辉石麻粒岩和麻粒岩相变质的堇青石榴矽线石片麻岩。二辉石麻粒岩的矿物组合为单斜辉石-斜方辉石-黑云母-角闪石-斜长石-石英。堇青石榴矽线石片麻岩矿物组合为堇青石-矽线石-石榴石-黑云母-斜长石-石英。岩石学和矿物学特征表明它们是典型的低压麻粒岩相变质岩石，其变质作用经历了两期演化：a．峰期麻粒岩相变质，T=681～705℃，P=5．4～5．8kbar；b．峰后角闪岩相退变阶段，T：571～637℃．P=4．7～5．3kbar。其变质作用P-T轨迹具有逆时针近等压降温(IBC)的特点，代表该地区可能为塔里木板块向伊犁．中天山板块俯冲过程中，在陆壳一侧所产生的陆源岩浆弧区域，由于受到下部岩浆热源的影响，在拉伸环境下出现低压麻粒岩相变质。通过分析低压麻粒岩相岩石与其南部高压一超高压变质带的大地构造位置和年代关系，我们认为该地区的低压麻粒岩相变质岩石可能与其南部的西天山高压一超高压变质带组成了双变质带。  相似文献   

Palaeoproterozoic granitic magmatism in the northern segment of the Jiao-Liao-Ji Belt: implications for orogenesis along the Eastern Block of the North China Craton     

Chao Li  Zhuang Li  Chuan Yang 《International Geology Review》2018,60(2):217-241

As the northern segment of the Jiao-Liao-Ji Belt (JLJB), the Palaeoproterozoic Liaoji Belt is a key region for deciphering the formation and evolution of the North China Craton (NCC). In this study, we present the geochronology, geochemical, and isotopic studies on the monzogranitic gneiss, which is one of the major lithotectonic elements of the Liaoji Belt. LA-ICP-MS zircon U–Pb dating reveals that the studied monzogranitic gneisses were formed in the period of 2213–2178 Ma. They are in tectonic contact with the Palaeoproterozoic volcano-sedimentary rocks in the field. The monzogranitic gneisses belong to the high-K calc-alkaline series, and are metaluminous to peraluminous. They have 10,000 Ga/Al ratios of 2.63–3.14 with an average of 2.90, and are thus classified as aluminous A-type granites. Their ε_Nd(t) values vary from ?3.4 to +2.5, indicating heterogeneous source region. The monzogranitic gneisses are characterized by enrichment in LREE and LILE (e.g. Rb, Ba, Th, and K) and depletion in HREE and HFSE (such as Nb, Ta, and Ti), and are typical to magmatism in active continental margins formed in a subduction-related tectonic setting. Taking into account their A-type affinity and regional geological data, we suggest that the monzogranitic gneisses were most probably generated in a local extensional back-arc environment during subduction.  相似文献   

吉林南部太古宙英云闪长质片麻岩类的特征及成因     

孙德有  葛文春  吴福元  周永胜 《吉林大学学报(地球科学版)》1995,(4)

吉林南部太古宙英云闪长质片麻岩类主要由石英闪长质、英云闪长质、花岗闪长质和奥长花岗质片麻岩组成。地质学、岩相学、地球化学研究表明，它们是同源岩浆通过结晶分异作用形成的，最主要的分离矿物相是角闪石和斜长石。岩浆来源于下地壳角闪质岩石的部分熔融作用。  相似文献   

豫西宜阳地区TTG质片麻岩锆石U-Pb定年和Hf同位素地质学   总被引：13，自引：19，他引：13  

第五春荣 孙勇林慈銮  柳小明王洪亮 《岩石学报》2007,23(2):253-262

本文报道对华北地块南缘、豫西宜阳穆册TTG质片麻岩的地球化学、锆石U-Pb定年及Hf同位素研究。宜阳穆册TTG质片麻岩SiO_2含量为59～73%,Al_2O_3>15%、CaO、MgO、Al_2O_3、TiO_2、Na_2O/K_2O与SiO_2的含量呈负相关,表明在岩浆演化中有镁铁矿物和斜长石的分离,岩浆成分随着分异而富钾。P_2O_5与SiO_2含量呈正相关,反映出磷灰石的分离。轻重稀土分异明显((La/Yb)_N=9～23);重稀土相对于轻稀土轻度分异;无明显的Eu异常(Eu*=0.95～1.07)。岩石富Rb、Sr、Ba、K等大离子亲石元素,亏损Nb、Ta等高场强元素。低Y(13.25～25.27μg/g)和Yb(1.27～1.98μg/g);高Sr(507.14～606.85μg/g)及Sr/Y(34.15～39.97),上述地球化学特征一致表明,研究区片麻岩为一套高铝的TTG质岩石。这套片麻岩可能是在角闪岩相条件下部分熔融的产物。利用LA-ICP-MS锆石U-Pb法测得TTG质片麻岩的年龄为2.3Ga。片麻岩中的锆石大部分具负ε_(Hf)(t)值(最高达-4.95),揭示其源区可能主要为古老陆壳物质;部分锆石的ε_(Hf)(t)为正值,说明在其形成过程中有一定比例的亏损地幔物质的加入。宜阳TTG质片麻岩的Hf同位素数据表明,其两阶段模式年龄主要2.57～3.01Ga之间,平均值为2.82Ga,所以说穆册灰色片麻的源区可能存在年龄为2.8Ga左右(或更老)的地壳物质,说明代表该区基底的太华杂岩形成时代可能为2.8Ga(或更老)。虽然华北地块陆壳最主要的增生时代被认为发生在2500Ma,但宜阳TTG质片麻岩的研究结果和其他研究者的研究成果都说明华北地块大陆地壳在古元古代早期仍然存在相当规模的陆壳增生。  相似文献   

http://www.sciencedirect.com/science/article/pii/S167498711400067X   总被引：1，自引：0，他引：1  

Timo G.Nijland  Daniel E.Harlov  Tom Andersen 《地学前缘(英文版)》2014,5(5):635-658

The Proterozoic Bamble Sector, South Norway, is one of the world＇s classic amphiboliteto granulite- facies transition zones. It is characterized by a well-developed isograd sequence, with isolated ＇granulite-facies islands＇ in the amphibolite-facies portion of the transition zone. The area is notable for the discovery of C02-dominated fluid inclusions in the granolite-facies rocks by Jacques Touter in the late 1960＇s, which triggered discussion of the role of carbonic fluids during granulite genesis. The aim of this review is to provide an overview of the current state of knowledge of the Bamble Sector, with an emphasis on the Arendal-Froland-Nelaug-Tvedestrand area and off shore islands （most prominantly Tromay and Hisoy） where the transition zone is best developed. After a brief overview of the history of geological research and mining in the area, aspects of sedimentary, metamorphic and magmatic petrology of the Bamble Sector are discussed, including the role of fluids. Issues relevant to current geotectonic models for SW Scandinavia, directly related to the Bamble Sector, are discussed at the end of the review.  相似文献   

华北克拉通阜平杂岩中~2.7GaTTG片麻岩的厘定及其地质意义   总被引：7，自引：7，他引：0  

路增龙  宋会侠  杜利林  任留东  耿元生  杨崇辉 《岩石学报》2014,30(10):2872-2884

通过详细的地质工作,本文从阜平杂岩中厘定出一套~2.7Ga的条带状TTG片麻岩系,其原岩主要为英云闪长岩,经历了强烈的变形和深熔改造。该片麻岩可分为岩石主体和条带,按条带形态和成分可分为三种:细小的暗色条带、深熔浅色条带和后期注入的长英质脉体。用LA-MC-ICPMS法对英云闪长岩中锆石进行了原位U-Pb年龄测试,其形成年龄为2669.2±9.7Ma。该片麻岩SiO2=64.32%~70.02%,具有高铝(Al2O3=14.00%~15.87%)富钠(Na2O=3.85%~4.22%)贫钾(K2O=1.13%~2.42%)及低K/Na比值的特点,Mg#指数为39.5~49.6。该片麻岩具有中等-强烈程度的稀土元素分异[(La/Yb)N=3.67~51.38],Eu异常不明显。其富集Sr(303×10-6~431×10-6)、Ba(191×10-6~696×10-6)等大离子亲石元素,亏损Nb(4.70×10-6~9.78×10-6)、Ta(0.19×10-6~0.75×10-6)、Ti(1378×10-6~3259×10-6)、P(174.6×10-6~960.6×10-6)等高场强元素,Cr(5.87×10-6~119.4×10-6)、Ni(6.72×10-6~45.75×10-6)等相容元素含量也较低。Yb(0.31×10-6~1.75×10-6)和Y(3.61×10-6~18.88×10-6)含量低,Sr/Y比值高(16.0~119.1),属于高铝的TTG,与高硅埃达克岩特征相似。推断是热的太古宙新生洋壳部分熔融而成。阜平地区~2.7Ga TTG片麻岩的厘定,进一步证实了华北克拉通在新太古代早期经历了强烈的陆壳增生,并为华北克拉通早期岩浆事件与世界范围的岩浆事件的对比提供了新的依据,为华北克拉通早期陆块及绿岩带的划分提供了新的限定。  相似文献   

Tectono-metamorphic evolution of the Karakorum Metamorphic complex (Dassu–Askole area, NE Pakistan): exhumation of mid-crustal HT–MP gneisses in a convergent context     

Y. Rolland  G. Mahéo  S. Guillot  A. Pecher 《Journal of Metamorphic Geology》2001,19(6):717-737

The South Karakorum margin, east of the Himalayan syntaxis, consist of an E–W elongated zone of young (10–3 Ma) high‐grade metamorphic rocks (M2) and related migmatitic domes. This late tectono‐metamorphic event post‐dates the Palaeogene (55–37 Ma) phase of thickening of the belt featured by NW–SE structures and associated M1 amphibolite facies metamorphism (0.7 GPa, 700 °C). This M2 metamorphism is characterised by low‐pressure, high‐temperature conditions coeval with migmatite formation in response to a thermal increase of c. 150 °C compared to M1, culminating at a temperature of c. 770 °C and a pressure of 0.5–0.6 GPa. Rapid exhumation of migmatitic domes, at a rate of 5 mm yr^?1, was accommodated by vertical extrusion, in the core of E–W crustal‐scale folds. These crustal‐scale folds formed in response to N–S syn‐collisional shortening and were enhanced by thermal weakening of the migmatised continental crust. M2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity, firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid‐crustal level. Such relationships between a mantle‐related magmatism and a high‐temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted Indian slab since 20 Ma.  相似文献   

P–T–fluid evolution in the Mahalapye Complex, Limpopo high-grade terrane, eastern Botswana     

K. HISADA  L. L. PERCHUK  T. V. GERYA  D. D. VAN REENEN  B. K. PAYA 《Journal of Metamorphic Geology》2005,23(5):313-334

Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P–T–fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high‐grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well‐developed textures inferred to record metasomatic reactions, such as Bt ? And + Qtz + (K₂O) and Bt ± Qtz ? Sil + Kfs + Ms ± Pl, and zonation of Ms | Bt + Qtz | And + Qtz and Grt | Crd | Pl | Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO₂ and H₂O ( = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P–T path. The P–T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low‐pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga.  相似文献