黑龙江省鸡西盆地基性岩40Ar/39Ar同位素定年及其地质意义   总被引：2，自引：0，他引：2  

朱占平  刘立  马瑞  邱增凯  马胜晖 《吉林大学学报(地球科学版)》2009,39(2):238

黑龙江省鸡西盆地张新地区辉绿玢岩呈岩床状侵入晚中生代城子河组地层中;辉绿玢岩较纯净,无捕虏体,呈斑状结构,斑晶由普通辉石、斜长石组成,斑晶体积分数为35%～40%;基质由微晶斜长石、辉石、磁铁矿及玻璃质组成。辉绿玢岩⁴⁰Ar/³⁹Ar同位素定年结果表明,其等时线年龄与坪年龄在误差范围内较为接近,该辉绿玢岩的形成时代介于96～101 Ma,即形成于早白垩世晚期-晚白垩世早期的Albian-Cenomanian阶。结合区域上该期岩浆事件的特点,暗示早白垩世晚期-晚白垩世时期鸡西盆地处于古太平洋板块(Izanagi-Kula 板块 )向东亚大陆边缘斜向俯冲背景之下的弧后伸展环境。  相似文献   

Origin and Geological Significance of TTG Gneisses from the Maevatanana Greenstone Belt in North–Central Madagascar, and A Comparison with India     

LI Peng  LI Jiankang  LIU Shanbao  PEI Rongfu  SHI Guanghai 《《地质学报》英文版》2017,91(3):1003-1024

The Maevatanana greenstone belt in north-central Madagascar contains widespread exposures of tonalite-trondhjemite-granodiorite(TTG) gneisses,and is important for its concentrations of various metal deposits(e.g.,chromium,nickle,iron,gold).In this paper we report on the petrography,and major and trace element compositions of the TTG gneisses within the Berere Complex of the Maevatanana area,as well as LA-ICP-MS U-Pb ages and Lu-Hf isotopic compositions of zircons from the gneisses.The gneisses consist mainly of granitoid gneiss and biotite(±hornblende) plagiogneiss,and analysis of thin sections provides evidence of crushing,recrystallization,and metasomatism related to dynamic metamorphism.Samples have large variations in their major and trace element contents,with SiO_2 = 55.87-68.06 wt%,Al_2O_3 = 13.9-17.8 wt%,and Na_2O/K_2O =0.97-2.13.Geochemically,the granitoid gneisses and biotite plagiogneisses fall on a low-Al trondhjemite to granodiorite trend,while the biotite-hornblende plagiogneisses represent a high-Al tonalite TTG assemblage.Zircon U-Pb dating shows that the Berere Complex TTG gneisses formed at2.5-2.4 Ga.Most ε_(Hf(t)) values of zircons from the biotite(± hornblende) plagiogneisses are positive,while most ε_(Hf(t)) values from the granitoid gneisses are negative,suggesting a degree of crustal contamination.Two-stage Hf model ages suggest that the age of the protolith of the TTG gneisses was ca.3.4-2.6 Ga,representing a period of paleocontinent formation in the Mesoarchean.Geothermometries indicate the temperature of metamorphism of the TTG gneisses was 522-612℃.Based on these data,the protolith of the TTG gneisses is inferred to have formed during the development of a Mesoarchean paleocontinent that is now widely exposed as a TTG gneiss belt(mostly lower amphibolite facies) in the Maevatanana area,and which records a geological evolution related to the subduction of an ancient oceanic crust and the collision of microcontinents during the formation of the Rodinia supercontinent.The lithological similarity of Precambrian basement,the close ages of metamorphism within greenstone belts and the comparable distribution of metamorphic grade all show a pronounced Precambrian geology similarity between Madagascar and India,which can provide significative clues in understanding the possible Precambrian Supercontinent tectonics,and also important constraints on the correlation of the two continental fragments.  相似文献   

Geneses of Two Types of Mafic Rocks to Carry Placer‐Magnetite Ores in the Sanin Granitic Belt,SW Japan          下载免费PDF全文

Shunso Ishihara  Hideo Hirano 《Resource Geology》2017,67(1):103-108

Two types of mafic rocks from the central Sanin district, and their mafic minerals, were studied chemically and microscopically. They are classified into pyroxene‐containing gabbroid and hornblende–biotite quartz diorite. The gabbroid had higher color index but lower magnetite content; while the quartz diorite had lower color index, but higher magnetite content. The magnetite contents are also related to the amounts of hydrous mafic silicates. The gabbroic magma having pyroxene–amphibole assemblage, originated in the upper mantle, was considered essentially anhydrous, but became partly hydrous on the way to the site of solidification in the continental crust, and crystallized some magnetites with hypersthene and amphibole. The quartz dioritic magma was formed by partial melting of possibly subducting ocean‐floor basalts, once exposed to the sea‐floor then altered; thus the magmas became hydrous and oxidized originally, and precipitated abundant magnetite and hydrous mafic silicates from the early crystallization stage onward. Their weathered parts provided the most placer magnetite ores in the history.  相似文献   

玉树北部二叠纪镁铁质岩的成因及其对大陆弧后盆地形成的指示     

刘彬  蔡昊龙  马昌前  吴栾  程琦  李福林  孙洋 《岩石矿物学杂志》2024,43(2):344-359

系统地调查与研究弧后盆地岩浆作用能为探究汇聚板块边缘的壳幔相互作用、板块俯冲动力学和弧后盆地形成-演化机制等提供重要信息。本文以最近在青海玉树北部地区发现的二叠纪镁铁质岩类为研究对象,开展了岩相学、锆石U-Pb年代学、岩石地球化学与同位素地质学等研究,以期为深入认识大陆弧后盆地形成机制及有关镁铁质岩浆的起源提供关键线索。锆石LA-ICP-MS U-Pb年代学测定结果表明,玉树北部辉长岩的结晶年龄为260±1 Ma。玄武岩样品具有相对低的TiO₂和Nb/Y值以及相对高的Ce/Nb值,其相对于原始地幔要显著富集轻稀土和Th等元素,亏损Nb、Ta、Ti和P等元素,可与世界上典型弧后盆地玄武岩(例如Okinawa Trough BABBs)成分特征类比。而辉长岩样品具有相对高的TiO₂和Nb/Y值以及相对低的Ce/Nb值,其相对于原始地幔要显著富集轻稀土和Th等元素,轻微亏损Nb、Ta和Ti,总体上具有与OIB类似的成分特征。玄武岩样品具有变化较大的ISr(0.706～0.709)和εNd(t)值(-1.8～+1.3),而辉长岩样品则具有相对均一的I...  相似文献   

Mineral chemistry and genesis of the Permian Cihai and Cinan magnetite deposits,Beishan, NW China     

《Ore Geology Reviews》2017

Cihai and Cinan are Permian magnetite deposits related to mafic-ultramafic intrusions in the Beishan region, Xinjiang, NW China. The Cihai mafic intrusion is dominantly composed of dolerite, gabbro and fine-grained massive magnetite ore, while gabbro, pyrrhotite + pyrite-bearing clinopyroxenite and magnetite ore comprise the major units in Cinan. Clinopyroxene occurs in both deposits as 0.1–2 mm in diameter subhedral to anhedral grains in dolerite, gabbro and clinopyroxenite. High FeO contents (11.7–28.9 wt%), low SiO₂ (43.6–54.3 wt%) and Al₂O₃ contents (0.15–6.08 wt%), and low total REE and trace element contents of clinopyroxene in the Cinan clinopyroxenite imply crystallization early, at high pressure. This clinopyroxene is FeO-rich and Si and Ti-poor, consistent with the clinopyroxene component of large-scale Cu-Ni sulfide deposits in the Eastern Tianshan and Panxi ares, as well as Tarim mafic intrusion and basalt, implying the Cinan mafic intrusion and sulfide is related to tectonic activity in the Tarim LIP. The similar mineral chemistry of clinopyroxene, apatite and magnetite in the Cihai and Cinan gabbros (e.g., depleted LREE, negative Zr, Hf, Nb and Ta anomalies in clinopyroxene, lack of Eu anomaly in apatite and similarity of oxygen fugacity as indicated by V in magnetite), indicate similar parental magmatic characteristics. Mineral compositions suggest a crystallization sequence of clinopyroxenite/with a small amount of sulfide – gabbro – magnetite ore in the Cinan deposit, and magnetite ore – gabbro – dolerite in Cihai. The basaltic magma was emplaced at depth, with magnetite segregation (and formation of the Cinan magnetite ores) occurring in relatively low fO₂ conditions, after clinopyroxenite and gabbro fractional crystallization. The evolved Fe-rich basaltic magma rapidly rose to intermediate or shallow depths, forming an immiscible Fe-Ti oxide magma as fO₂ increased and leaving a Fe-poor residual magma in the chamber. The residual magmas was emplaced at different levels in the crust, forming the Cihai gabbro and dolerite, respectively. Finally, the immiscible Fe-Ti oxide magma was emplaced into the earlier formed dolerite because of late magma pulse uplift, resulting in a distinct boundary between the magnetite ores and dolerite.  相似文献   

An extensional and transtensional origin of elongated magmatic domes and localised transfer faults in the northern Menderes metamorphic core complex,western Turkey     

Fuat Erkül  Sibel Tatar Erkül  Hatice Seval Manap  Cihan Çolak 《Geodinamica Acta》2017,29(1):139-159

The northern Menderes metamorphic core complex has complex exhumation history and is one of the key localities to investigate the spatial and temporal relationships of extensional and compressional structures. Detachment faults and syn-extensional plutons are linked to a series of antiforms and synforms and the denudation of the northern Menderes Massif occurred in three stages. The first stage is related to the development of detachment faults under the consistent NE–SW-directed extension. The second stage is represented by a series of elongated magmatic domes that were oriented parallel, oblique and perpendicular to the regional extension direction. Emplacement of these asymmetrical magmatic domes appears to have been controlled by heterogeneous extension and post-dates the extensional Simav detachment fault. On the third stage, progressive heterogeneous extension that led to updoming of plutons has been finally accommodated by a localised and short-lived transfer zone, which was described as the Gerni shear zone for the first time in this study. The transfer zone is formed by a NE-striking, dextral ductile/brittle shear zone that accommodated the propagation of folds, conjugated strike-slip faults and normal- and oblique-slip faults. Mylonites associated with the transfer zone are related to the localisation of strain along the thermally weakened strike-slip fault systems by short-lived intrusions rather than to the development of regional-scale detachment faults. These structures are consistent with a transtensional simple shear model, which properly explains the evolution of extensional and compressional structures exposed in the northern Menderes core complex. Structural setting of the E?rigöz region is somewhat similar to that of the NE-trending gneiss domes in the northern Menderes Massif and updoming of magma during late stages of detachment faulting appears to have played an important role in the exhumation of lower and upper plate rocks.  相似文献   

云母片（麻）岩风化料填筑路基的性能研究     

姚占勇  练继建  张西斌  房建国 《岩土力学》2006,27(Z1):611-614

通过室内试验,研究了高云母含量的云母片（麻）岩风化料的压实性能、水稳定性、CBR等工程特性。结果表明,由于云母片表面极光滑, 且具有高弹性,大量云母片的存在使得风化料颗粒间嵌挤能力差,抗剪能力低,在击实过程中易出现表层起皮、松散和回弹现象;其水稳定性差,强度偏低,CBR值达不到高速公路上路床填料的强度标准;增加击实功,不能明显改善材料的压实性能;利用该类材料填筑路基,宜采用静压施工,避免振动碾压。对该类材料采用黏土、风化砂、水泥改性后,可明显改善材料的压实性能,提高材料的强度。从工程经济的角度提出了合理的改性材料外掺剂量。  相似文献   

P-T-X (CO₂) conditions in mafic and calc-silicate hornfelses from Oberon, New South Wales, Australia     

A. S. ANDREW 《Journal of Metamorphic Geology》1984,2(2):143-163

Abstract The Rockley Volcanics from near Oberon, New South Wales occur within the aureole of the Carboniferous Bathurst Batholith and have been contact metamorphosed at P ∼ 100 ± 50MPa (10.5kbar) and a maximum T ∼ 565°C in the presence of a C–O–H fluid. Prior to contact metamorphism the volcanics were regionally metamorphosed and altered with the extensive development of actinolite, chlorite, plagioclase, quartz and calcite. The contact metamorphosed equivalents of these rocks have been subdivided into: Ca-poor (cordierite + gedrite), Mg-rich (amphibole + olivine + spinel), mafic (amphibole + plagioclase) and Ca-rich (amphibole + garnet + diopside; diopside + plagioclase; garnet + diopside + wollastonite) rocks.
The chemistry of the minerals in the hornfelses was controlled by the bulk rock chemistry and fluid composition. Pargasites and hastingsites as well as an unusual phlogopite with blue green pleochroism, are found in Ca-rich hornfelses. A comparison of the assemblages with experimentally derived equilibria suggests that the fluid phase associated with the Ca-rich hornfelses was water-rich (X_co2= 0.1 to 0.3) while that associated with the Mg-rich hornfelses was enriched in CO₂ (X_co2 > 0.7). The different hornfels types have reacted to contact metamorphism independently in both their solid and fluid chemistries.  相似文献   

Nb/Ta variations of mafic volcanics on the Archean- Proterozoic boundary: Implications for the Nb/Ta imbalance     

LIU Yongsheng    GAO Shan    WANG Xuance  HU Shenghong & WANG Jianqi . State Key Laboratory of Geological Processes  Mineral Resources  China University of Geosciences  Wuhan  China  . Key Laboratory of Continental Dynamics  Department of Geology  Northwest University  Xi’an  China 《中国科学D辑(英文版)》2005,48(8):1106-1119

Hofmann[1] found that the depleted mantle (DM) and bulk continental crust (BCC) are simply compen-satory in terms of many elements and elemental ratios. High-field-strength elements (HFSE) (e.g., Zr, Hf, Nb, Ta and Ti) are immobile and thus useful to track the primary features of the ancient mafic volcanics. It has been long considered that Nb-Ta behave as identical twins during magmatic processes, based on their matching atomic radii and valence state and hence coherent geochemical affi…  相似文献   

苏鲁超高压变质带西北缘五莲断裂外侧浅变质花岗片麻岩的地球化学特征与原岩成因研究   总被引：6，自引：0，他引：6       下载免费PDF全文

薛怀民  刘福来  许志琴 《中国地质》2005,32(2):249-258

五莲杂岩中的正片麻岩主要为正长花岗质片麻岩，少数石英正长质片麻岩，具有适度碱性的演化趋势。以贫CaO、低MgO、高Na2O为特征，岩石中虽然碱度较高，但仍属较强过铝型。这套正片麻岩还表现为较强的轻、重稀土元素分馏程度和强的负Eu异常，尤以强烈富集大离子亲石元素（Rb、Ba、Th、U、K)和亏损高场强元素Ti、Zr、Hf．Nb、Ta(部分样品中Zr、Hf除外)，明显的Ba、P负异常为显著特征。岩石地球化学的总体特征与苏鲁造山带内的花岗质片麻岩有一定的可比性，而与华北克拉通内的前寒武纪正片麻岩明显不同。推测五莲地区正片麻岩的原岩是晚元古代由大陆下地壳富钾的变质玄武质组分部分熔融形成的，母岩浆的演化主要表现为以长石(奥长石和钾长石)的分离结晶为主，其中可能还有少量黑云母和角闪石，以及副矿物锆石和磷灰石的分离结晶。  相似文献