Regional progressive high-pressure metamorphism, Seward Peninsula, Alaska   总被引：1，自引：0，他引：1  

R. B. FORBES  B. W. EVANS  S. P. THURSTON 《Journal of Metamorphic Geology》1984,2(1):43-54

Abstract Blueschist-facies rocks on the Seward Peninsula constitute a structurally coherent terrane measuring at least 100 × 150 km. Radiometric age data indicate that high-pressure metamorphism probably occurred in Jurassic rather than in Palaeozoic or Precambrian time, as previously suggested. Protolith sediments (Nome Group) are of intracontinental basin or continental margin type, and of lower Palaeozoic and possibly late Precambrian age, thus predating the high pressure metamorphism by more than 200 m.y. Blueschist-facies mineral assemblages were developed in almost all lithologies of the Nome Group, and are best preserved in FeTi-rich metabasites (glaucophane + almandine + epidote) and pelites (glaucophane + chloritoid + phengite). A lawsonite–crossite subfacies was developed in possible Nome Group rocks on the east flank of the Darby Mountains. Albite–epidote–amphibolite facies assemblages characterize Nome Group rocks in the southwestern part of the Peninsula. Metamorphism in the central zone of the terrane passed from early lawsonitic to subsequent epidote–almandine–glaucophane schist subfacies with the local development (east of the Nome River) of eclogitic assemblages. The high pressure metamorphic minerals were synkinematic with the development of mesoscopic-scale intrafolial isoclinal folds and a flattening foliation of consistent orientation. Initiation of uplift probably corresponded to the growth of barroisite rims on earlier sodic and actinolitic amphiboles, and partial post-kinematic greenschist facies replacements record later stages of decompression. Ophiolites and melange are not associated with the Seward Peninsula blueschists. The high-pressure metamorphism was caused by tectonic loading of a continental plate by an allochthon of indeterminate origin. The PT conditions of high pressure metamorphism were approximately 9–11 kbar, 400–450°C, thus falling between the PT paths of the Shuksan and Franciscan terranes.  相似文献   

辽宁高家堡子银矿区石榴云母片岩地球化学特征及地质意义     

郑岩  杨言辰  韩世炯  杨宇 《世界地质》2017,36(3):785-795

石榴云母片岩是高家堡子银矿区重要的容矿围岩。岩石地球化学分析显示,石榴云母片岩具有副变质岩特征,富集大离子亲石元素(Th,K),亏损高场强元素(Nb,Ta,Ti),稀土元素总量较高(ΣREE均值169.28×10~(-6)),轻、重稀土元素分馏明显,轻稀土元素富集,具有δCe弱正异常,δEu中等负异常。野外观察结合地球化学特征研究,高家堡子银矿区石榴云母片岩原岩为泥岩、砂岩、杂砂岩,具有上地壳长英质物源特征,形成环境为被动大陆边缘环境。  相似文献   

Tectonic Setting of the Kadiri Schist Belt, Andhra Pradesh, India     

Sukanta GOSWAMI  Pradeep K. UPADHYAY  Purnajit BHATTACHARJEE  Malaiandi G. MURUGAN 《《地质学报》英文版》2017,91(6):1992-2006

Plate tectonic activity has played a critical role in the development of petrotectonic associations in the Kadiri schist belt. The calc alkaline association of basalt, andesite, dacite and rhyolite(BADR) is the signature volcanic rock suite of the convergent margin. The N-S belt has gone below the unconformity plane of Cuddapah sediments. In the northern part geochemical and structural attributes of the Kadiri greenstone belt is studied along with microscopic observations of selected samples. Harker diagram plots of major elements generally indicate a liquid line of descent from a common source, such that BADR rocks are derived from a common parent magma of basaltic to andesitic composition. These calc-alkaline volcanic rocks are formed at convergent margins where more silicic rocks represent more highly fractionated melt. All the litho-units of this greenstone belt indicate crush and strain effects. The stretched pebbles in the deformed volcanic matrix with tectonite development along with associated greenschist facies metamorphism, alteration and hydration is remarkable. Flow foliation plane with N-S strike and very low angle(5° to 10°) easterly dip and N-S axial planar schistosity formed due to later phase isoclinal folding can be clearly identified in the field. Basic intrusives are quite common in the surrounding area. All the observations including the field setting and geochemistry clearly demonstrate ocean-continent subduction as the tectonic environment of the study area.  相似文献   

基于损伤演化的片岩应力松弛特性     

刘志勇  肖明砾  谢红强  何江达 《岩土力学》2016,37(Z1):101-107

为揭示丹巴水电站石英云母片岩的各向异性松弛性特及松弛过程中的损伤演化规律,针对平行片理组和垂直片理组石英云母片岩,采用程控蠕变试验仪,开展为期720 h的单轴应力松弛试验。试验发现,平行片理组和垂直片理组岩样的应力松弛曲线均可分为快速松弛、减速松弛和稳定松弛3个阶段,属于非完全衰减型松弛类型;受片理发育方向影响,平行片理组应力衰减历时较垂直片理组长。结合石英云母片岩的应力松弛特征,将基于能量耗散的损伤因子代入Bingham模型流变本构方程,利用改进Euler差分算法推导应力松弛方程,并用神经网络法对模型参数进行辨识。研究表明,平行片理组与垂直片理组在快速松弛阶段损伤发展较快,且随着松弛过程的进行损伤速率逐渐降低至稳定,损伤演化与应力松弛过程是统一的;考虑损伤演化的Bingham流变模型拟合曲线与试验结果具有较高的吻合度,说明文中提出的松弛方程能很好地描述石英云母片岩的应力松弛特性,对软岩工程研究具有较高的应用价值。  相似文献   

Tectonics of an Early Carboniferous forearc inferred from a high-P/T schist-bearing conglomerate in the Nedamo Terrane, Northeast Japan     

Takayuki  Uchino  Makoto  Kawamura 《Island Arc》2010,19(1):177-191

The Nedamo Terrane, an Early Carboniferous accretionary complex, is the oldest biostratigraphically dated accretionary complex in Japan. The purpose of this study is to describe and interpret a conglomerate from the Nedamo Terrane that contains clasts of high-pressure/low-temperature (high- P/T ) schist (mainly garnet-bearing phengite schist) and ultramafic rock, and to infer the tectonics of an Early Carboniferous arc–trench system at the eastern margin of the paleo-Asian continent. Clasts of high- P/T schist and ultramafic rock within the conglomerate make up 8.4 and 6.7% of the total clasts, respectively, based on modal counts. These clasts are subangular to subrounded, whereas volcanic clasts are well rounded. The source of the schist clasts, which yield a radiometric age of 347–317 Ma, is considered to be the Renge Metamorphic Rocks of Southwest Japan or equivalent rocks. Based on the chemical composition of chromian spinel, the source of ultramafic clasts is inferred to be the island-arc-type Ordovician Miyamori and Hayachine ultramafic complexes in the Kitakami Massif. The conglomerate records multiple provenance regions, including an island arc (South Kitakami Terrane) and a forearc ridge; the high P/T schist and ultramafic rocks were exhumed in the forearc region. The duration of the interval from the early stages of exhumation of the schist to its deposition in the trench as clasts is estimated to have been less than 30 my.  相似文献   

绢云母片岩路基填料最大填筑粒径确定方法     

谈云志  喻波  戴光柏  王乐华  付伟 《岩土力学》2015,36(1):137-142

绢云母片岩是一种易崩解的片岩填料,在大气的长期干湿循环作用下,性能极易发生衰减、弱化。通过开展干湿循环前后不同初始最大粒径绢云母片岩的加州承载比试验和回弹模量试验,探讨其强度变化规律,并结合颗粒分析试验,从崩解的角度解释上述强度变化原因。结果表明,绢云母片岩在经历10次干湿循环作用后颗粒再无明显崩解,粒径为10 mm的颗粒可作为其崩解强弱的分界点,粒径大于10 mm的颗粒崩解较快,粒径小于10 mm的颗粒崩解较慢。绢云母片岩的回弹模量在初始最大粒径为5～10 mm时较大;而其承载比在初始最大粒径为10～20 mm时较大。结合崩解特性,选取初始最大粒径10 mm作为绢云母片岩路基填筑的控制粒径。  相似文献   

不同应力路径下绢云母片岩粗粒料声发射特征   总被引：1，自引：0，他引：1  

秦尚林  杨兰强  高惠  陈善雄 《岩土力学》2015,36(1):89-96

粗粒料在变形和颗粒破碎过程中伴随着明显的声发射（AE）,通过监测粗粒料在外力作用下的声发射信号特征可用来研究其力学机制。为探讨不同应力路径下绢云母片岩粗粒料声发射规律,采用改装设计的大型三轴试验机,对绢云母片岩粗粒料分别开展了常规三轴固结排水、等p（体应力）和等q（偏应力）应力路径试验,同时监测其声发射信号。研究表明,对于粗粒料的声发射必须考虑颗粒间的滑动摩擦、翻滚摩擦、颗粒破碎这3种细观机制。不同围压、不同应力水平对颗粒间的滑移、翻滚以及颗粒破碎活动影响较大,因此,在不同阶段,摩擦型AE与破碎型AE所占比例各不相同。在等p路径下,当累计声发射信号出现拐点时,可判断其为应变软化点。等q试验产生的累计AE计数与累计AE能量计数要比等p试验的累计AE计数和累计AE能量计数少一个量级,说明等p试验状态下的声发射要比等q试验活跃。等p试验中,随着体应力逐渐增大,累计AE参量增长率逐渐增大,而等q试验中,随着偏应力逐渐增大,累计AE参量增长率逐渐降低。  相似文献   

谷竹高速公路原状片岩抗剪强度的水敏性研究   总被引：1，自引：0，他引：1  

刘建  李建朋 《岩土力学》2012,33(6):1719-1723

为了解鄂西北地区水敏性片岩在水作用下的抗剪强度特性,对取自谷竹高速公路现场的原状片岩试样开展了沿其层理面的室内天然状态直剪试验和饱水状态直剪试验,试验结果表明：水对片岩的抗剪强度和破坏特征影响显著;饱水后片岩与天然状态相比凝聚力降低了36.7%,内摩擦角降低了4.6%,残余凝聚力降低了66.7%,残余内摩擦角降低了11.3%;与天然状态的脆性破坏不同,饱水后片岩破坏时具有明显的延性特征。基于试验结果,探讨了水对片岩抗剪强度参数的弱化机制,利用极限平衡方法计算了谷竹高速公路沿线某边坡的安全系数,进而对该边坡在暴雨或连续降雨工况下的稳定性做出了评价。  相似文献   

风化片岩残积土剪切特性研究     

刘胜利  陈善雄  刘伟  余飞  罗红明  赵文光 《岩土力学》2013,34(12):3520-3526

为考察片岩残积土的剪切特性,结合鄂西北山区某边坡工程,开展了风化岩残积土大型原位直剪试验,研究了风化岩残积土的结构组成、剪切面破损特性、剪切强度特性及其含石率、起伏度等相关关系。结果表明：该风化岩残积土应力-应变曲线多呈应变硬化特征,无明显峰值;束状孤石和束状石组多为翻滚和啃断破坏,起伏度随含石率的增大而增大,近似呈线性关系;爬坡效应会引起剪胀,造成剪应力和垂直应力的增大;随着垂直应力的增大,剪切破坏机制逐渐由滑移破坏变为啃断破坏,剪压应力比（剪应力与垂直应力的比值）逐渐减小。研究成果可为边坡工程变形及稳定性分析提供参考。  相似文献