内蒙古西部巴彦乌拉山地区花岗闪长岩质片麻岩的单颗粒锆石U-Pb法年龄   总被引：9，自引：1，他引：9  

李俊建沈保丰  李惠民周红英郭利军  李超英 《地质通报》2004,23(12):1243-1245

巴彦乌拉山位于内蒙古西部阿拉善盟境内,该区出露的地层以片麻岩为主,夹斜长角闪岩。由于无确切的同位素年龄资料熏这套岩石时代的归属一直存在不同认识。本文最近获得的花岗闪长质片麻岩的单颗粒锆石U-Pb法年龄为(2082±22)Ma,是迄今为止该区获得的较为可靠的直接测年数据。这将改变原认为这套片麻岩形成于太古宙的认识,对该区区域地质调查和矿产勘查评价具重要意义。  相似文献   

Diffusion creep and partial melting in high temperature mylonitic gneisses, Hope Valley shear zone, New England Appalachians, USA   总被引：2，自引：1，他引：2  

S. R. Garlick  L. P. Gromet 《Journal of Metamorphic Geology》2004,22(1):45-62

Field, petrographic, microstructural and isotopic studies of mylonitic gneisses and associated pegmatites along the Hope Valley shear zone in southern Rhode Island indicate that late Palaeozoic deformation (c. 275 Ma) in this zone occurred at very high temperatures (>650 °C). High‐energy cuspate/lobate phase boundary microstructures, a predominance of equant to sub‐equant grains with low internal lattice strain, and mixed phase distributions indicate that diffusion creep was an important and possibly predominant deformation mechanism. Field and petrographic evidence are consistent with the presence of an intergranular melt phase during deformation, some of which collected into syntectonic pegmatites. Rb/Sr isotopic analyses of tightly sampled pegmatites and wall rocks confirm that the pegmatites were derived as partial melts of the immediately adjacent, isotopically heterogeneous mylonitic gneisses. The presence of syntectonic interstitial melts is inferred to have permitted a switch from dislocation creep to melt‐enhanced diffusion creep as the dominant mechanism in these relatively coarse‐grained mylonitic gneisses (200–500 µm syn‐deformational grain size). A switch to diffusion creep would lead to significant weakening, and may explain why the Hope Valley shear zone evolved into a major regional tectonic boundary. This work identifies conditions under which diffusion creep operates in naturally deformed granitic rocks and illuminates the deformation processes involved in the development of a tectonic boundary between two distinct Late Proterozoic (Avalonian) basement terranes.  相似文献   

太行山区片麻岩裸地分类及其林业利用     

马平安  李庆辰  段惠敏 《山地学报》1998,(2)

根据成土母岩的矿物构成、风化特性、风化层的保存状况和坡度,将太行山区裸露片麻岩坡地分为三类、七亚类和三个林业利用等级.提出了不同级别片麻岩裸地的最佳造林树种和林业利用途径.  相似文献   

郯庐断裂中段鲁中基底韧性变形带的形成时代     

周建波  胡克  孙加鹏 《地质通报》1998,(2)

郯庐断裂中段鲁中基底的韧性变形带可分为两类：（１）北东向韧性变形带,以发育中深层次的构造片麻岩为特征,形成于早中元古代花岗质岩体（２４８８Ｍａ）侵位之前;（２）北北东向韧性变形带,以中浅层次糜棱岩为特征,形成于晋宁期（９４１Ｍａ）。文中对以上两类韧性变形带的形成机制和时代进行了初步讨论。  相似文献   

Mesozoic doming extensional tectonics of Wugongshan, South China   总被引：4，自引：0，他引：4  

Liangshu Shu  Yan Sun  Dezi Wang  M. Faure  P. Monie  J. Charvet 《中国科学D辑(英文版)》1998,41(6):601-608

Wugongshan in Jiangxi Province, China was a Mesozoic granitic dome-type extensional tectonics that is composed of metamorphic core complexes, ductile and brittle shear-deformed zones distributed around Mesozoic granites. Within it, the foliation defines an E-W elliptical shape and bears S-N stretching lineations. The axial part is located in Hongjiang-Wanlongshan area and occupied by oriented granites with coaxial symmetric shear fabrics. The southem and northern flanks, including rocks in the Anfu Basin to the south and the Pingxiang Basin to the north, display top-to-south and top-to-north motions, respectively. The ductile and brittle structures indicate a geometric and kinematic consistency. The extensional tectonics is developed on a Caledonian metamorphic basement and is unconformably covered by Late Cretaceous red beds. Isotopic ages on muscovite, biotite and whole rock by⁴⁰Ar-³⁹Ar, K-Ar and Rb-Sr suggest that the Wugongshan extensional doming began from the Triassic and ended in the Late Cretaceous. A geodynamic model is discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 49632080, 49572141)  相似文献   

Implications from the seismic crustal structure of the northern Izu–Bonin arc     

NARUMI  TAKAHASHI  KIYOSHI  SUYEHIRO & MASANAO  SHINOHARA 《Island Arc》1998,7(3):383-394

The results of a controlled source seismic reflection–refraction experiment carried out in 1992 reveal the following characteristics of the northern Izu–Bonin (Ogasawara) oceanic island arc–trench system. (1) The crust rapidly thickens from the Shikoku back-arc basin to the arc, is thickest beneath the active rifts, and then gradually thins to the forearc. The thickness of the crust beneath the arc rift zone and the back-arc basin are ∼ 20 km and 8 km, respectively. (2) The Moho vanishes beneath the forearc. Velocities rapidly decrease eastwards beneath the inner trench wall. (3) The velocity of the lower crust of the arc and the back-arc basin is 7.1–7.3 km/s. This velocity is higher than the typical oceanic lower crust whose velocity is ∼ 6.7 km/s. (4) The velocity of the middle crust of the arc is ∼ 6 km/s. This layer does not exist beneath the back-arc basin. (5) A slight difference in the velocity gradient of the middle crust exists between the arc rift zone and the forearc. Based on these findings and previous studies, it is inferred that: (i) the middle crust is probably granitic rock and formed in more than two episodes; (ii) the lower crust formed by igneous underplating which may also have affected part of the back-arc basin; and (iii) the root of the serpentinite diapir on the inner trench wall is a low-velocity mantle wedge that was probably caused by large amounts of water released from the subducting Pacific plate at depths shallower than 30 km.  相似文献   

阿尔泰可可托海3号伟晶岩脉中铌铁矿族矿物环带构造及其岩石学意义   总被引：4，自引：0，他引：4       下载免费PDF全文

张爱铖  王汝成胡欢张辉  朱金初谢磊 《地质学报》2004,78(2):181-189

本文利用电子探针和背散射电子成像技术系统地研究了新疆阿尔泰可可托海3号伟晶岩脉各结构带中的铝铁矿族矿物。研究表明,本区伟晶岩脉中铌铁矿族矿物主要为铌锰矿-钽锰矿。成分特征显示从岩脉边部带到核部,Ta/(Nb Ta)比值呈近垂向演化,但Mn/(Fe Mn)比值没有明显变化。另一方面,铌铁矿族矿物在早期正岩浆阶段(Ⅰ-Ⅳ带)的成分变化非常局限,而在晚期的岩浆-热液过渡阶段(Ⅴ-Ⅶ带)的成分变化非常大。背散射电子成像技术观察还表明本区铌铁矿族矿物在正岩浆阶段没有环带构造特征,而在岩浆-热液过渡阶段有明显的环带构造特征,而且随着伟晶岩固结过程的进行,环带构造主要沿着渐变环带构造→韵律环带构造→交代构造的趋势变化。研究认为,本区铌铁矿族矿物在不同结构带的成分变化和在单颗粒中的环带构造是热液流体参与铌铁矿族矿物结晶的反应,环带构造的类型主要是由热液流体参与结晶的程度所控制。  相似文献   

花岗质熔体中SnO₂含量与结晶温度和时间的关系   总被引：3，自引：0，他引：3  

李福春  朱金初  饶冰  金章东  张林松 《矿床地质》2002,21(4):393-398

锡石在花岗质熔体中的溶解度，是阐明花岗岩全岩型锡矿成因的关键。文章设计了以结晶温度和结晶时间为参数的两组熔化-结晶实验。试图模拟锡石在岩浆结晶分异过程中的动态变化，并在花岗岩-HF-H2O体系的高温高压实验结果基础上，讨论花岗岩质熔体中SnO2含量与结晶温度和时间的关系。实验结果表明：（1）在岩浆条件下可以形成锡石；（2）随着结晶温度的降低和时间的加长，熔体中SnO2含量先升高后降低，表明其经历了由不饱和到过饱和，进而结晶出锡石的动态过程。  相似文献   

Igneous origin of K-feldspar megacrysts in deformed granite of the Papoose Flat Pluton, California, USA     

R. H. Vernon  S. R. Paterson 《Visual Geosciences》2002,7(1):1-28

Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat pluton are residual phenocrysts, not porphyroblasts. Evidence of an igneous origin includes features such as crystal shapes, simple twinning, zonally arranged euhedral plagioclase inclusions, oscillatory compositional zoning, and local occurrence in microgranitoid enclaves. Evidence of solid-state deformation of the megacrysts (which is consistent with their existence prior to the mylonitic deformation) includes marginal recrystallization and neocrystallization, microcline twinning, marginal replacement by myrmekite, and recrystallized/neocrystallized “tails”. Evidence of porphyroblastic growth, such as overgrown inclusion trails, is absent. This appears to be the situation in most felsic augen gneisses and mylonites.  相似文献   

富锂氟含稀有矿化花岗质岩石的对比和成因思考   总被引：31，自引：5，他引：31  

朱金初  饶冰  熊小林  李福春  张佩华 《地球化学》2002,31(2):141-152

Li-F花岗质岩石以超酸性、过铝、富含H2O、F、B、P等挥发性组分和富含Li、Rb、Cs、Be、Ta、Nb、Sn、W等亲石稀有金属元素为主要特征，以黄玉－锂云母－钠长石花岗岩为典型代表。从该类岩石地质产状的多样性和可对比性、空间分布的规律性、矿物岩石的结构构造、硅酸盐－熔体包裹体特征以及实验岩石学的研究成果等方面，综合论证该类岩石主要是从经过分异演化而形成的残余熔浆中直接结晶而在的；充分的分离结晶作用，是产生这种残余熔浆的主要机制；岩体的空间分带特征和各带之间的渐变过渡关系，为分离结晶作用的途径和演化方向提供了重要信息；熔体中挥发性组分的大量存在，是分离结晶作用能充分进行的关键因素；亲石稀有金属元素在流／熔配分中倾向于进入熔体相，是残余熔体中逐步富集这些稀有金属元素的主要原因；岩浆－热液过渡阶段出溶的流体相与已晶出的共存固相之间的相互作用，造成了广泛的交代蚀变现象；残余熔浆在不同地质和物理化学环境中的侵位、结晶和演化，造成了Li-F花岗质岩石在产状、结构构造和矿物组合等方面的多样性。  相似文献