The muscovite-melt bathograd and low-P isograd suites in north-central Wopmay Orogen, Northwest Territories, Canada     

MARC R. ST-ONGE 《Journal of Metamorphic Geology》1984,2(4):315-326

In north-central Wopmay Orogen, syntectonic low-P(Buchan-type) suites of mineral isograds outline regional metamorphic temperature culminations that are associated, at the higher structural levels, with emplacement of early Proterozoic plutons in the west part of a deformed and eastward transported continental margin prism. The mapped isograds mark the first occurrence of biotite, staurolite, andalusite, sillimanite, sillimanite-K feldspar and K feldspar-plagioclase-quartz ± muscovite (granitic) pods in metapelites, with increasing proximity to the plutons.
Microprobe analyses and field observations have resulted in the formulation of reactions for the 'ideal'pelitic system K₂O-Na₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O-Al₂O₃-SiO₂-H₂O, to account for the various mineral assemblages of each metamorphic zone. A P-T petrogenetic grid showing erosion surface P-T curves for the northern Wopmay Orogen pelites, compiled on the basis of the mapped isograds and the inferred reaction(s) for each metamorphic zone, documents a variation in exposed metamorphic pressure ranging between 2 and 4 kbar.
The configuration of a new bathograd, based on the invariant model reaction sillimanite + K feldspar + plagioclase + biotite + quartz + vapor ± muscovite + liquid and interpolated across three metamorphic suites, is consistent with a major regional structure culmination and with independently determined pressures obtained from anorthite-grossular-quartz-Al₂SiO₅ geobarometry. The positive correlation between the configuration of the bathograd and the structural and pressure culmination points to the pressure-dependence of anatectic-granitic-pod mineral associations.  相似文献   

Pyrite Re–Os and muscovite 40Ar/39Ar dating of the Beizhan iron deposit in the Chinese Tianshan Orogen and its geological significance     

Shigang Duan  Zuoheng Zhang  Dachuan Wang  Zongsheng Jiang  Wenjuan Luo  Fengming Li 《International Geology Review》2018,60(1):57-71

The Awulale iron metallogenic belt (AIMB) hosts the majority of rich iron ores in Tianshan Orogen and has attracted much attention. However, a hot debate exists about the genesis of these iron deposits. Geochronological data are among the few critical evidences to solve the dispute. This study chooses the Beizhan iron deposit to carry out a geochronological research. The Beizhan magnetite deposit, with total iron ore reserves of 468 Mt at an average grade of 41% TFe, is the largest iron deposit in the AIMB. The orebodies of the Beizhan deposit are hosted in Carboniferous dacite and crystal tuff. Four stages of mineral formation can be recognized: an early skarn mineral stage, followed by the magnetite stage, the sulphide stage, and the carbonate stage in order. Pyrite separated from pyrite-rich ore samples yields an isochron age of 302.5 ± 8.2 Ma. Muscovite separated from muscovite-rich ore samples yields ⁴⁰Ar/³⁹Ar plateau ages of 304.7 ± 1.8 Ma, 304.5 ± 1.9 Ma, 308.1 ± 1.9 Ma, and 307.2 ± 1.8 Ma, and isochron ages of 306.1 ± 3.5Ma, 304.0 ± 3.0Ma, 308.2 ± 3.1Ma, and 308.7 ± 3.1Ma, respectively. These ages are consistent within the error range and are interpreted as the age of the Beizhan iron deposit. The results, combined with the other latest precise dating and geologically inferred ages, demonstrate that the iron deposits in the AIMB were formed in the Late Carboniferous. These iron deposits are considered to be iron skarn or medium–low -temperature hydrothermal origin and have genetic linkages between each other. They may be different mineralizing manifestations proximal to or distal from a pluton. The Late Carboniferous iron ores and the related magmatic rocks in the AIMB were produced when upwelling of the asthenosphere causes the partial melting of various sources and the formation of a narrow linear extension in the upper crust. The upwelling of the asthenosphere may be triggered by the detachment of an orogenic root zone.  相似文献   

桂西北地区石英斑岩脉白云母40Ar/39Ar 年龄及其地质意义   总被引：3，自引：0，他引：3  

陈懋弘  陆刚  李新华 《高校地质学报》2012,18(1):106-116

华南西部右江褶皱带内部燕山晚期岩浆岩主要为成群分布的基性- 超基性岩墙群和超酸性岩脉带。本文对桂西北巴
马-凤山-凌云一带的石英斑岩脉进行了斑晶白云母40Ar/39Ar 法测年,获得凤山弄黄北东向岩脉的40Ar/39Ar 坪年龄为（95.59
±0.68）Ma,相应的等时线年龄为（95.0±1.0）Ma;巴马北西向岩脉的坪年龄为（96.54±0.70）Ma,相应的等时线年龄为
（95.91±1.1）Ma。上述年龄代表了岩脉的侵位年龄。这些年龄数据进一步证明右江褶皱带及其周缘燕山期岩浆活动集中于
80~100 Ma 之间,暗示该区晚白垩世发生了大规模的岩石圈伸展减薄事件。华南西部晚白垩世花岗质岩浆活动与大规模的
锡多金属成矿有关,因此桂西北地区石英斑岩集中出露的地方是否具有寻找深部锡多金属矿的前景值得关注。同时,该期
岩浆活动是否与以卡林型金矿为代表的低温热液矿床有成因上的联系尚需更多矿床地质和年代学资料的证实。  相似文献   

“江南造山带”变质基底形成的构造环境及演化特征   总被引：11，自引：0，他引：11  

王自强  高林志  丁孝忠  黄志忠 《地质论评》2012,58(3):401-413

"江南造山带"变质基底的形成和演化长期存在不同认识。本文试图通过区域地层对比、火山—沉积组合、构造变形特征,大量新的测年数据以及淡色花岗岩(MPG)和含堇青石花岗闪长岩(CPG)等岩体的分布及产出的构造环境分析,再次探讨"江南造山带"变质基底的构造环境和演化特征。笔者等认为"江南造山带"变质基底的形成和演化与1.1～0.9Ga的"格林威尔运动"无关,它是Rodinia超大陆裂解后的不同陆块(如扬子陆块、华夏陆块等)的大陆边缘沉积,经830～780Ma之晋宁运动期碰撞造山,进而构成新元古代中—晚期扬子古陆新的増生大陆边缘。晋宁期碰撞造山的特征是:在时间演化方面经历了早期初始强烈碰撞、挤压变形—松弛拉张接受不同规模裂陷盆地或裂谷火山—碎屑沉积—终期再碰撞演化过程;在空间变化方面则显示为构造环境的多样性。以湘、赣边界剪切断裂带和鄱阳湖—赣江剪切断裂带为界,形成三种不同的构造环境。湘黔桂代表的西部区段和赣西北代表的中部区段均为被动大陆边缘的陆—陆对接碰撞构造环境。但二者在挤压和拉张强度和规模的差别,导致两区段构造形态的不同。赣皖浙东部区段为活动大陆边缘具多列岛弧及弧后盆地的洋—陆俯冲—碰撞构造环境。  相似文献   

Mineralogical feature and geological significance of muscovites from the Longyuanba Indosinian and Yanshannian two-mica granites in the eastern Nanling Range     

TAO JiHua  LI WuXian  CAI YuanFeng  CEN Tao 《中国科学:地球科学(英文版)》2014,57(6):1150-1157

Emplacement P-T condition estimations using granites are important for understanding metamorphic and erosional processes of orogenic belt.Granites are widespread in South China and a majority of them are peraluminous.Particularly,over 91%of the Indosinian granites exposed in the region are peraluminous in composition.It is extremely hard to determine the pressure of intrusion of these peraluminous granites due to the absence of amphibole,a good mineral barometer commonly identified in metaluminous granites.Muscovite is a common mineral in peraluminous granites,certain kind of it could be used as a mineral barometer to constrain the emplacement pressure of peraluminous granites.In this paper,results of petrographic and geochemical studies of muscovites from the Indosinian and early Yanshanian two-mica granites at the Longyuanba in the eastern Nanling Range are reported.Based on petrographic studies,the primary muscovite can be discriminated from the secondary muscovites.Muscovites from the Indosinian two-mica granites are enriched in Ti,Al,Mg,and Na,and depleted in Fe and Mn.Geochemically,these muscovites were considered as primary,whereas those from the Yanshanian two-mica granites fall into the area of secondary muscovite on discrimination diagrams.Barometer estimations show that pressures calculated for primary muscovites are accurate,but those calculated for secondary muscovites are overestimated.The average pressure of emplacement of the Longyuanba Indosinian two-mica granites is 5.9 kbar,corresponding to~19 km in depth,suggesting that the Indosinian granitic magmas were probably generated by partial melting of a thickened crust root in a compressional tectonic setting.  相似文献   

藏南错那洞淡色花岗岩成因：来自全岩地球化学和锆石U-Pb年龄的约束     

黄春梅  李光明  张志  梁维  黄勇  张林奎  付建刚 《地学前缘》2018,25(6):182-195

藏南错那洞穹隆位于喜马拉雅造山带东部,淡色花岗岩是其核部组成部分之一。对其中的弱定向二云母花岗岩和含石榴子石二云母花岗岩进行LA-ICP-MS锆石U-Pb定年,显示其结晶年龄分别为(20.6±0.3) Ma和(16.7±0.2) Ma,属于喜马拉雅中新世淡色花岗岩。错那洞含石榴子石二云母花岗岩和弱定向二云母花岗岩均具有富硅(w(SiO2)为71.6%~74.6%)、富铝(w(Al2O3)为14.5%~16.1%)、富钾(w(K2O)为4%~4.7%)及高铝饱和指数(A/CNK=1.16~1.22)的特征,属高钾钙碱性系列的强过铝质花岗岩,并且两类花岗岩都富集Rb、U、K、Pb,相对亏损Nb、Ta、Zr、Ti。但含石榴子石淡色花岗岩具有明显的Eu负异常(Eu/Eu*=0.29~0.46),而弱定向二云母花岗岩Eu的负异常相对较弱(Eu/Eu*=0.58~0.80)。弱定向二云母花岗岩的Rb/Sr值为2.4~3.5,Ba含量为(200~253)×10-6,TiO2含量相对较低,表明错那洞弱定向二云母花岗岩是在无水条件下由变泥质岩中的白云母脱水熔融而形成,并且弱定向二云母花岗岩的产生可能与藏南拆离系(STDS)启动造成的构造减压有关。含石榴子石二云母花岗岩的K/Rb、Zr/Hf、Nb/Ta、Y/Ho值呈现出非球粒陨石异常,稀土四分组效应和异常高的Rb/Sr值(18.6~22.2)表明错那洞含石榴子石二云母花岗岩是经过岩浆高度演化而形成的。高度演化的岩浆有利于W、Sn、Be等稀有金属成矿。错那洞含石榴子石二云母花岗岩与错那洞穹隆的W-Sn-Be矿具有相邻的空间位置,两者之间可能存在一定的成因联系;而错那洞弱定向二云母花岗岩与扎西康Pb-Zn矿床在时间上和空间上都具有一致性,两者之间很可能也存在一定的成因联系。  相似文献   

云南来利山锡矿床白云母标型特征研究          下载免费PDF全文

王冬丽  申俊峰  董国臣  刘圣强  张弘 《中国地质调查》2017,4(2):59-65

来利山锡矿床作为滇西地区著名的锡多金属矿床之一,为了探讨其矿床成因,为找矿勘探提供科学依据,对该矿区白云母进行标型特征研究。研究表明: 白云母是该矿区的重要矿物之一,主要分布在第一、二成矿阶段及其附近围岩中; 在光学显微镜下,成矿阶段白云母多呈竹叶状或扇状(放射状)集合体,围岩中白云母呈半自形—自形,解理清晰; 电子探针数据显示,不同成矿阶段的白云母成分略有差异,说明其成因受到成矿热液演化影响; 围岩中的白云母成分显示为多硅白云母,Na-Mg图解显示,围岩主要为中低温、中—高压环境,其中变质砂岩为高压环境,褪色角岩为高—中压环境。上述成果对于该区进一步找矿工作具有指导意义。  相似文献   

离心分层距离法——一种定量表征聚合物液体中矿物填料沉降性能的方法     

汪灵  关淞云  赵熠  张瑜  付海英 《矿物岩石》2009,29(1)

研究聚合物等高粘度液体中矿物填料的沉降性能,可以为新型绝缘灌注胶以及矿物材料研究与应用提供科学依据,根据斯托克斯公式和离心沉降速度公式以及高速旋转离心实验特点,时自然沉降时间计算公式进行推导.并根据绝缘灌注胶特点以及不同粒度微晶白云母在环氧树脂中高速离心沉降实验,总结出一种能够对聚合物等高粘度液体中矿物填料的沉降性能进行快速定量表征的离心分层距离法;实验结果表明:微晶白云母在E-51环氧树脂中的沉降速度和分层比例都分别与其粒度大小呈正比关系,1 000目完全沉降(分层比例100%)需要7 068.7 d,其自然沉降速度为0.7×10-7mm·s-1,若要保持3个月内不发生明显的分层现象,应当采用1 000目或更细小的粒度.  相似文献   

40Ar/39Ar Thermochronological Constraints on the Timing of Collisional Orogeny in the Mian-Lüe Collision Belt,Southern Qinling Mountains     

LI Jinyi  WANG Zongqi  ZHAO Min 《《地质学报》英文版》1999,73(2):208-215

Silurian, Devonian and Carboniferous geological bodies in the Mianxian-Lüeyang (Mian-Lüe) collisional belt (MLB) and its neighbouring areas, southern Qinling Mountains, China, show similar characteristics of having undergone deformation of two stages. The earlier one, which is inferred to be related to collisional orogeny between the Yangtze and Sino-Korean palaeocontinents based on previous geological data, is responsible for large-scale, north-verging recumbent folds and overthrusts, and associated with low greenschist facies metamorphism. 40Ar/39Ar dating of three muscovite samples taken from different localities yields plateau ages of 226.9(0.9 and 219.5(1.4 Ma and an apparent age of 194.5(3.0 Ma. Thus, the late Triassic collision between the Yangtze and Sino-Korean palaeocontinents has been constrained.  相似文献   

赣北大湖塘平苗矿段白云母花岗岩锆石U-Pb年代学、地球化学及地质意义     

余振东  项新葵  谭荣  孙德明  张斯 《吉林大学学报(地球科学版)》2020,50(5):1505-1517

赣北大湖塘钨铜多金属矿集区位于扬子板块东南缘、江南造山带中段,是近年来查明的世界级钨矿产地之一。对大湖塘平苗矿段中粗粒白云母花岗岩进行了岩相学、锆石U-Pb年代学、地球化学及成矿作用的研究,结果表明,此花岗岩内白云母显示原生白云母的特性,LA-ICP-MS锆石U-Pb年龄为（145.7±0.6）Ma,与区内细粒黑云母花岗岩测试年龄相近,系同源岩浆演化结晶分异的结果,为燕山期多期次岩浆侵入的第二阶段。燕山期岩石单元先后有似斑状黑（二）云母花岗岩→细粒黑云母花岗岩、白云母花岗岩→花岗斑岩,白云母花岗岩是区内重要的成矿地质体之一。地球化学研究表明,该白云母花岗岩为高分异S型花岗岩,具有高硅（w（SiO₂）=73.14%~74.19%）、富碱、过铝质的特征及较高的分异指数,轻重稀土分馏明显,呈左高右低的深V型,Eu表现为强烈的亏损,存在REE四分组效应,Rb/Sr、Rb/Ba的平均值分别为151.81和245.21,表明岩浆是经历多阶段分离结晶、高度分异的结果。  相似文献