An Archean(?) to Paleozoic Evolution for a Garnet Peridotite Lens with Sub-Baltic Shield Affinity within the Seve Nappe Complex of Jamtland, Sweden, Central Scandinavian Caledonides   总被引：2，自引：0，他引：2  

BRUECKNER  HANNES K.; VAN ROERMUND  HERMAN L. M.; PEARSON  NORMAN J. 《Journal of Petrology》2004,45(2):415-437

Mineralogical, isotopic, geochemical and geochronological evidencedemonstrates that the Friningen body, a garnet peridotite bodycontaining garnet pyroxenite layers in the Seve Nappe Complex(SNC) of Northern Jämtland, Sweden, represents old, certainlyProterozoic and possibly Archean, lithosphere that became incorporatedinto the Caledonian tectonic edifice during crustal subductioninto the mantle at c. 450 Ma. Both garnet peridotite and pyroxenitecontain two (M₁ and M₂) generations of garnet-bearing assemblagesseparated by the formation of two-pyroxene, spinel symplectitearound the M₁ garnet and the crystallization of low-Cr spinel_1Cin the matrix. These textures suggest initial high-pressure(HP) crystallization of garnet peridotite and pyroxenite succeededby decompression into the spinel stability field, followed byrecompression into the garnet peridotite facies. Some pyroxenitelayers appear to be characterized solely by M₂ assemblages withstretched garnet as large as several centimeters. Laser ablationmicroprobe–inductively coupled plasma mass spectrometryRe–Os analyses of single sulfide grains generally definemeaningless model ages suggesting more than one episode of Reand/or Os addition and/or loss to the body. Pentlandite grainsfrom a single polished slab of one garnet peridotite, however,define a linear array on an Re–Os isochron diagram that,if interpreted as an errorchron, suggests an Archean melt extractionevent that left behind the depleted dunite and harzburgite bodiesthat characterize the SNC. Refertilization of this mantle bymelts associated with the development of the pyroxenite layersis indicated by enriched clinopyroxene Sr–Nd isotope ratios,and by parallel large ion lithophile-enriched trace elementpatterns in clinopyroxene from pyroxenite and the immediatelyadjacent peridotite. Clinopyroxene and whole-rock model Sm–Ndages (T_DM = 1·1–2·2 Ga) indicate that fertilizationtook place in Proterozoic times. Sm–Nd garnet₂–clinopyroxene₂–wholerock ± orthopyroxene₂ mineral isochrons from three pyroxenitelayers define overlapping ages of 452·1 ± 7·5and 448 ± 13 Ma and 451 ± 43 Ma (2  相似文献   

Rupture Property of the 1927Gulang Ms8.0 Earthquake and Numerical Simulation of Rupture Mechanism1     

Zheng Wenjun 《中国地震研究》2005,19(4):409-419

The 1927 Gulang M_S8.0 earthquake is a severe earthquake that followed the Haiyuan M_S8.5 earthquake of 1920 in the Qilian Mt._Hexi Corridor earthquake zone. There are divergences of opinion in the previous studies about the rupture properties of the earthquake. Based on trenching and field investigation, and analysis of historical data, we hold that the earthquake resulted from the joint process of the Tianqiaogou_Huangyangchuan fault, Dongqingding segment of the Huangcheng_Shuangta fault and the Wuwei_Tianzhu buried fault, which constitute the Gulang nappe. By finite_element numerical simulation on the deformation mechanism of Gulang nappe, it is found that the stress and strain mainly concentrate in the western segment of the Tianqiaogou_Huangyangchuan fault, the Dongqingding segment of the Huangcheng_Shuangta fault, and the Gulangxia segment of the Wuwei_Tianzhu buried fault and the Gulang_Shuangta fault. The stress concentration coincides with the distribution of the earthquake surface rupture. It also proves that the earthquake is an outcome of the Gulang nappe activity as a whole.  相似文献   

青城子地区早元古宙辽吉岩套的构造演化     

刘俊来 《国土资源》1991,(2)

本文讨论了辽东青城子地区早元古宙辽吉岩套的构造变形作用与构造演化。作者提出了青城子推覆构造的三阶段演化模式。早期阶段,即第1变形幕形成了北西向转南西向的同斜倒转褶皱,构成了青城子推覆体的雏形;第2变形幕以剪切体制为主,辽吉花岗岩活化和底辟重就位形成了推覆体构造,并产生了逆冲型韧性剪切带;第3变形幕形成了叠加在推覆体构造上的北东向倾伏背斜、向斜构造,并使推覆体构造发生整体机械变位,最终奠定了青城子地区的宏观构造格局。  相似文献   

New evidence of a magmatic arc in the southern Brasília Belt,Brazil: The Serra da Água Limpa batholith (Socorro-Guaxupé Nappe)     

《Journal of South American Earth Sciences》2014

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New 40Ar/39Ar constraints for the “Grande Nappe”: The largest rhyolitic eruption from the Mont-Dore Massif (French Massif Central)     

Sébastien Nomade  Jean-François Pastre  Alison Pereira  Alexandra Courtin-Nomade  Vincent Scao 《Comptes Rendus Geoscience》2017,349(2):71-80

Since the 1960s, an early explosive activity in the Mont-Dore Massif is associated with a major pyroclastic rhyolitic eruption (5–7 km³) known as the “Grande Nappe” (GN). This event, linked to the formation of a 6-km-diameter cryptic caldera named “Haute Dordogne”, was before our investigation dated by ⁴⁰Ar/³⁹Ar at 3.07 ± 0.04 Ma. Our new single-crystal laser fusion ⁴⁰Ar/³⁹Ar dates obtained on two outcrops of the GN (Rochefort-Montagne and Ludières) questioned several hypotheses made concerning this “landmark” event of the Mont-Dore Massif history. We demonstrate that: (1) the GN rhyolitic eruption has occurred much later than previously estimated (i.e. 2.77 ± 0.02–0.07 Ma full external uncertainties); (2) the correlation made between the Vendeix rhyolitic complexes (intra-caldera position) dated back to 2.74 ± 0.04 Ma and the GN is proposed; (3) xenocryst contamination could be very high (i.e. 70% for the Rochefort-Montagne GN outcrop) and explains the noticeable older age obtained previously; (4) a link between the GN eruption and the formation of a caldera is questionable; the hypothesis of a northward-oriented blast channeled eastward toward the paleo-Allier River is thus proposed.  相似文献   

天水街子温泉控热推覆构造的发现及地热前景探讨          下载免费PDF全文

罗文广  孙知新  安永康  李百祥 《甘肃地质》2006,15(1):68-71

天水街子温泉通过可控源音频大地电磁测深,在温泉所在的温家峡及其附近深部发现的低阻电性层呈层状分布,其深度与以往钻孔中所见地下热水部位一致,推断此低阻层为热水通道。结合地表地质和地面磁测推测逆断层与上盘推覆体(牵引背斜)构成推覆构造,逆冲断层为阻水构造,活动上盘岩块破碎和裂隙发育是地下热水良好通道,控制着中低温地热田分布。街子温家峡温泉和黄家峡有利热储地段,地下热水具有充沛的补给来源、较好储存和开采条件,具有进一步钻探开发扩大地热利用的远景。  相似文献   

北疆区域地质调查阶段性成果与新认识   总被引：4，自引：0，他引：4  

李荣社  计文化  校培喜  马中平  陈隽璐  潘术娟 《新疆地质》2012,30(3):253-257

在介绍北疆沿国境线1∶25万区调修测项目阶段性成果基础上,据1∶25万区域地质调查新获得的地质事实与进展,结合区域性路线地质考查资料,对新疆北部准噶尔盆地东部阿尔曼太(扎河坝)蛇绿构造混杂带和准西部玛依勒山蛇绿岩带成因和构造背景提出新认识,初步认为阿尔曼太(扎河坝)蛇绿构造混杂带是华力西—印支期由南向北高角度逆冲推覆断裂铲起了早古生代(额尔其斯-卡拉麦里断裂间)增生杂岩楔(蛇绿岩块)推覆构造带;玛依勒山蛇绿岩带是具准洋壳特征的超基性岩、玄武岩及火山碎屑岩、硅质岩组合地层体,弱变形面状的分布,不具板块构造界线属性,表明其可能为哈萨克板块东南部陆缘裂谷中产物.  相似文献   

云南普洱萝卜山铅锌矿隐伏矿找矿思路     

李章雄  刘丽华  纪辉 《云南地质》2012,(1):39-42

以区内发育大型逆冲推覆构造及已控制矿体为基础,根据逆冲推覆构造成矿理论,经野外实地调查和对已有地质资料的综合分析,提出在本区寻找隐伏矿体找矿思路。  相似文献   

粤北新洲推覆构造同推覆期岩石体积变化的估算及其地质意义     

彭少梅 《地球科学与环境学报》1994,(1)

非平面应变状态下岩石体积变化的估算，一直是世界上悬而未决的问题。本文初步完善了实用于非平面应变状态下岩石体积变化的计算公式，并用这些公式计算了粤北新洲推覆体同推覆期的岩石体积变化。结果表明，在逆冲推覆时期，整个外来系统普遍发生了强烈的压溶－迁出作用．由此造成的岩石体积损耗平均达２２．８８％。同推覆期外来系统的巨大体耗，与同推覆期含金动力分异热液的形成和演化以及该区石英脉型金矿床成矿物质来源之间有着密切的内在联系．  相似文献   

点苍山新生代推覆构造的确立及其地质意义   总被引：2，自引：0，他引：2  

沙绍礼 《云南地质》2002,21(3):250-255

点苍山地处三江构造带东缘，其东侧扬子陆块上的古生代地层，越过洱海断裂推覆到苍山西坡的中、新生代地之上：下泥盆统青山组推覆至下白垩统景星组之上；上二叠叠统乌龙坝组及红岩子组推覆在始新统宝相寺组之上。三江构造带中的上三维统歪古村组及三合洞组推覆在上侏罗统坝注路组之上。推覆时期为始新世－上新世，推覆构造机制是陆内汇聚挤压所至。  相似文献