Paleoproterozoic crustal evolution of the Hengshan–Wutai–Fuping region, North China Craton     

Chunjing Wei  ;Jiahui Qian  ;Xiwen Zhou 《地学前缘(英文版)》2014,5(4):485-497

An arguable point regarding the Neoarchean and Paleoproterozoic crustal evolution of the North China Craton（NCC）is whether the tectonic setting in the central belt during the mid-Paleoproterozoic（2.35-2.0 Ga）was dominated by an extensional regime or an oceanic subduction-arc regime.A review of the midPaleoproterozoic magmatism and sedimentation for the Hengshan-Wutai-Fuping region suggests that a back-arc extension regime was dominant in this region.This conclusion is consistent with the observation that the 2.35-2.0 Ga magmatism shows a typical bimodal distribution where the mafic rocks mostly have arc affinities and the acidic rocks mainly comprise highly-fractioned calc-alkaline to alkaline（or A-type）granites,and that this magmatism was coeval with development of extensional basins characteristic of transgressive sequences with volcanic interlayers such as in the Hutuo Group.Although the final amalgamation of the NCC was believed to occur at ～1.85 Ga,recent zircon U-Pb age dating for mica schist in the Wutai Group suggests a collisional event may have occurred at ～1.95 Ga.The metamorphic ages of ～1.85 Ga,obtained mostly from the high-grade rocks using the zircon U-Pb approach,most probably indicate uplifting and cooling of these high-grade terranes.This is because（i）phase modeling suggests that newly-grown zircon grains in highgrade rocks with a melt phase cannot date the age of peak pressure and temperature stages,but the age of melt crystallization in cooling stages;（ii）the metamorphic P-T paths with isobaric cooling under 6-7 kb for the Hengshan and Fuping granulites suggest their prolonged stay in the middle-lower crust;and（iii）the obtained metamorphic age data show a continuous distribution from 1.95 to 1.80 Ga.Thus,an alternative tectonic scenario for the Hengshan-Wutai-Fuping region involves：（i）formation of a proto-NCC at ～2.5 Ga;（ii）back-arc extension during 2.35-2.0 Ga resulting in bimodal magmatism and sedimentation in rifting basins on an Archean basement;?  相似文献   

Metamorphic P-T paths from calcic pelitic schists from the Strafford Dome, Vermont, USA     

T. MENARD  F. S. SPEAR 《Journal of Metamorphic Geology》1994,12(6):811-826

Metamorphism of the Gile Mountain Formation and Waits River Formation in the Strafford Dome and Townshend-Brownington Syncline in east-central Vermont records two nappe-style events, D1 and D2, followed by doming. D1 formed a muscovite + biotite ± ilmenite schistosity subparallel to compositional layering, SO, and was followed by heating to garnet grade. The temperature and pressure at the end of D1 are estimated to be c . 450 C and 6-8 kbar. D2 variably crenulated and folded S1 during a nearly isothermal pressure increase of 1-2 kbar, calculated from compositions of garnet, which have inclusions trails with progressive crenulation and rotation of the S1 fabric. Similar P-T paths are computed for most of the area, suggesting that the later schistosity developed during emplacement of a regional nappe 3-6 km thick. There is a general lack of D3 (dome-stage) microstructures.
Near the Strafford-Willoughby Arch, staurolite and kyanite overgrew S2 in pelites, and plagioclase with increasing X _An overgrew S2 in calcic pelites, reflecting post-D2 heating to a maximum of 550-600 C. Metamorphic pressures at the end of D2 are fairly constant on the west side of the dome, indicating minor dome-stage uplift. In contrast, pressures at the thermal peak of metamorphism decrease by more than 4 kbar east of the dome. The observed pattern of isotherms and isobars is mainly the result of post-metamorphic, differential uplift and unroofing.
Finally, a minor, retrograde metamorphism produced the assemblage albite + epidote + K-feldspar + muscovite + chlorite, with grade increasing east toward the Connecticut River.  相似文献   

秦岭沙河湾Ⅰ型花岗岩岩石学、矿物学特征及岩浆形成的温压条件   总被引：1，自引：0，他引：1  

刘春花  吴才来  雷敏  秦海鹏  李名则 《地质与勘探》2013,49(4)

南秦岭沙河湾岩体紧临商丹断裂南侧,是具有环斑结构的似斑状-粗粒结构石英二长岩.本文通过化学全分析、偏光显微镜、电子探针(EPMA)、扫描电镜(SEM)对沙河湾岩体的岩石学和矿物学特征进行了研究,并对岩浆形成的温压条件与构造背景进行了讨论.结果表明,主量元素SiO2=66.40％ ～70.08％,Al2O3=14.36％ ～ 14.95％,Fe2O3 =0.93％～1.73％,FeO=1.22％ ～ 1.65％,CaO=1.94％ ～2.78％,Na2O+ K2O=7.88％ ～8.56％,K2O/Na2O=1.02 ～ 1.11,δ＜3.3,为高钾钙碱性的过铝质Ⅰ型花岗岩类;∑REE平均151×10-6,LREE/HREE平均13.63,(La/Yb)N平均20.54,δEu平均0.89,δCe平均0.95,表明其轻稀土富集,重稀土亏损,Eu和Ce异常不明显,球粒陨石标准化配分曲线为右倾型,亏损Nb、Ce、Zr、Ti等高场强元素,略富Ba、K、Sr等大离子亲石元素;主要造岩矿物为石英、斜长石(更(奥)长石-钠长石)、钾长石、镁角闪石和镁质黑云母,副矿物为锆石、榍石、磁铁矿、钛铁矿和少量的石榴石等;初始岩浆温度平均755～ 780℃;角闪石和斜长石结晶温度约621～623℃;岩浆侵位深度约4km,压力约1.26×108Pa,具有壳幔混源的特点;沙河湾石英二长岩形成于中温、富水、中氧逸度的环境.  相似文献   

Three dimensional steady-state locus for dry monodisperse granular materials: DEM numerical results and theoretical modelling     

Irene Redaelli  Claudio di Prisco 《国际地质力学数值与分析法杂志》2019,43(16):2525-2550

In this paper, steady-state conditions for ideal monodisperse dry granular materials are both theoretically and numerically analysed. A series of discrete element (DEM) numerical simulations have been performed on a periodic cell by imposing stress paths characterized by different Lode angles, pressures, and deviatoric strain rates. The dependence of the material response on both inertial number and loading path has been discussed in terms of void ratio, fabric, and granular temperature. DEM numerical results have been finally compared with the prediction of an already conceived model based on both kinetic and critical state theories, here suitably modified to account for three-dimensional conditions.  相似文献   

利用投影影像精化数字表面模型     

陈艳楠  汪佳丽 《测绘通报》2020,(6):45

随着摄影测量技术的成熟和人们对摄影测量产品应用的要求不断提高，真正射影像在工程与人们生活中扮演越来越重要的角色。生成高质量真正射影像的关键在于如何获取高精度的DSM。目前修正和改善DSM误差的方法普遍存在费力费时、精度缺乏保证及任意性等问题。本文针对DSM精度的修正问题提出了一种新的方法，即基于投影影像的概念，将空间点位在投影影像上的投影轨迹线作为几何约束条件，直接对现有DSM的高程进行修正的方法。通过获取高精度的DSM，进而生成更为精确的真正射影像。本文通过理论推导、单点高程和多点高程修正试验，验证了提出的新方法直观简单，适用性强，具有一定的实际应用价值。  相似文献   

大别山南部高压-超高压变质地体的峰期变质条件   总被引：3，自引：2，他引：1       下载免费PDF全文

石永红  王清晨 《地质科学》2004,39(3):375-387,338

长期以来,人们普遍认同南大别高压超高压变质地体是由“冷”、“热”榴辉岩带组成的观点,但关于两者的接触关系一直存在着不同的认识。本次研究重点解剖大别山太湖地区花凉亭水库附近地区,力图通过对各类榴辉岩峰期变质P-T条件的研究,揭示南大别变质地体的地质结构。全区由南向北出露4种岩石:云母片岩、黑云母片麻岩、花岗片麻岩和绿帘黑云斜长片麻岩。榴辉岩多呈大小不等的透镜体、岩块或层状分布于后3类岩石中。根据内洽地质温压计的计算结果,并结合各类榴辉岩的地理位置,可以看出榴辉岩的峰期变质PT条件自朱家冲经水口、大坝至金河桥是渐次增高的,并没有明显的压力差存在,其中水口、大坝附近的榴辉岩相当于高压/超高压过渡环境中形成的榴辉岩。因此,我们认为南大别变质地体是一个连续的整体,“冷”、“热”榴辉岩带并不是以断层形式相接触的;真正的断裂应位于南大别与宿松群之间。  相似文献   

Phase Equilibria of Hornblende-Bearing Eclogite in the Western Dabie Mountain,Central China   总被引：1，自引：0，他引：1  

ZHANG Jingsen WEI Chunjing LOU Yuxing SU Xiangli Hebei University of Engineering  H  an  Hebei  China Key Laboratory of Orogenic Belts  Crustal Evolution  Ministry of Education  School of Earth  Space Sciences  Peking University  Beijing  China 《《地质学报》英文版》2009,83(1)

The high-pressure (HP) eclogite in the western Dabie Mountain encloses numerous hornblendes,mostly barroisite.Opinions on the peak metamorphic P-T condition,PT path and mineral paragenesis of it are still in dispute.Generally,HP eclogite involves garnet,omphacite, hornblendes and quartz,with or without glaucophane,zoisite and phengite.The garnet has compositional zoning with X_(Mg) increase,X_(Ca) and X_(Mn) decrease from core to rim,which indicates a progressive metamorphism.The phase equilibria of the ...  相似文献   

Mineral parageneses in metamorphic rocks exposed along Tailuko Gorge,Central Mountain Range,Taiwan*     

W. G. ERNST 《Journal of Metamorphic Geology》1983,1(4):305-329

Field, petrographic and microprobe investigations of metaclastic rocks, calcareous schists, marbles, chloritic calcareous meta-volcanic units and schists/paragneisses which crop out along the eastern portion of the Central East-West Cross Island Highway in Taiwan demonstrate that metamorphic intensity gradually increases eastward. The lower greenschist facies Slate Formation on the W contains completely recrystallized, pure albitic plagioclase, but at least some of the white micas (± chlorites) probably represent relict detrital flakes. Neo-blastic biotite and epidote occur sporadically in the Pihou(?) Formation, and increase dramatically eastward; concomitantly the abundance of carbonaceous matter decreases to zero in the eastern Tailuko zone, and the amount of chlorite + white mica diminishes somewhat. Epidote becomes more aluminous at higher metamorphic grade. Eastward, phengites change progressively to more muscovitic compositions as the proportion of biotite increases. A close approach to chemical equilibrium for the pre-Cenozoic, complexly deformed metamorphic basement assemblages is suggested by regular, systematic, major and minor element partitioning between analysed coexisting phases. Fractionation is less pronounced on the E, reflecting higher temperatures. Estimated physical conditions of recrystallization with α_H2O and α_CO2 moderate, are: T > 325 ± 75°C, P > 3 kbar (W); T > 425 ± 75°C, P > 4kbar(E). The gradual eastward increase in metamorphic intensity from the Slate Formation through the Pihou(?) Formation and the three Tailuko zones, as well as the relict precursor textures in the pre-Cenozoic layered basement rocks indicate that the observed paragenetic sequence could represent a synchronous Neogene recrystallization event, probably accompanying the Plio-Pleistocene collision of the Asiatic continental margin and the Luzon (Coastal Range) andesitic arc.  相似文献   

阜平地区麻粒岩的P－T路径研究   总被引：8，自引：1，他引：8  

刘树文 《高校地质学报》1996,(1)

阜平麻粒岩分布于阜平大柳树和坊里一带的原阜平超群下亚群索家庄组花岗质片麻岩中，以不同规模的透镜体、似层状体产出、麻粒岩主要由石榴石、单斜辉石、斜方辉石、角闪石和斜长石等矿物组成，含有少量的石英。根据岩石的矿物组合和结构特征可将其变质作用演化分为四个阶段：①石榴石中的角门石、斜长石、单斜辉石等变质矿物包体代表峰前阶段；②粗粒平衡共生的角闪石、单斜辉石、石榴石、斜长石±紫苏辉石±石英等代表了峰期变质阶段；③石榴石变斑晶后生合晶反应边中外侧细粒斜方辉石、斜长石和石英集合体代表了峰后变质阶段；④后生合晶反应边中内侧角门石、斜长石等，代表了晚期退化变质阶段。这四个变质阶段演化的Ｐ－Ｔ条件依次为：峰前阶段６３６℃、０．８２４ＧＰａ，峰期阶段７５１～８３３℃、０．８５４～１．０８５ＧＰａ，峰后阶段６７０～７４０℃、０．５５～０．７０ＧＰａ，退化变质阶段６６５℃、０．７２７ＧＰａ，构成了一条顺时针的Ｐ－Ｔ路径，反映了该变质区从早期褶皱增厚到晚期构造抬升的地质动力学过程。  相似文献   

赣中变质岩带的矿物化学特征及其P—T轨迹的构造变化     

胡恭任 《铀矿地质》2001,17(2):97-100

本文根据矿物组合及特征变质矿物，将赣中变质岩带划分出5条变质带，由低到高依次为绢云母－绿泥石（Ser-Chl)带、黑云母（Bi)带、铁铝榴石（Gt)带、十字石（St)带、矽线石（Sil)带。其分布的总体趋势是由南向北呈渐进分布的特点，即变质地层在纵向上由新到老具有由弱而强的变化趋势，同时受构造的控制。区域断裂带，从断裂中心向两侧变质程度递减，并常伴随混合岩化作用。本文从矿物化学特征及P、T条件计算结果来讨论变质岩的演化特征及形成的构造环境。  相似文献