排序方式： 共有11条查询结果，搜索用时 15 毫秒
1.
Reaction localization and softening of texturally hardened mylonites in a reactivated fault zone, central Argentina 总被引：6，自引：0，他引：6
The Tres Arboles ductile fault zone in the Eastern Sierras Pampeanas, central Argentina, experienced multiple ductile deformation and faulting events that involved a variety of textural and reaction hardening and softening processes. Much of the fault zone is characterized by a (D2) ultramylonite, composed of fine‐grained biotite + plagioclase, that lacks a well‐defined preferred orientation. The D2 fabric consists of a strong network of intergrown and interlocking grains that show little textural evidence for dislocation or dissolution creep. These ultramylonites contain gneissic rock fragments and porphyroclasts of plagioclase, sillimanite and garnet inherited from the gneissic and migmatitic protolith (D1) of the hangingwall. The assemblage of garnet + sillimanite + biotite suggests that D1‐related fabrics developed under upper amphibolite facies conditions, and the persistence of biotite + garnet + sillimanite + plagioclase suggests that the ultramylonite of D2 developed under middle amphibolite facies conditions. Greenschist facies, mylonitic shear bands (D3) locally overprint D2 ultramylonites. Fine‐grained folia of muscovite + chlorite ± biotite truncate earlier biotite + plagioclase textures, and coarser‐grained muscovite partially replaces relic sillimanite grains. Anorthite content of shear band (D3) plagioclase is c. An30, distinct from D1 and D2 plagioclase (c. An35). The anorthite content of D3 plagioclase is consistent with a pervasive grain boundary fluid that facilitated partial replacement of plagioclase by muscovite. Biotite is partially replaced by muscovite and/or chlorite, particularly in areas of inferred high strain. Quartz precipitated in porphyroclast pressure shadows and ribbons that help define the mylonitic fabric. All D3 reactions require the introduction of H+ and/or H2O, indicating an open system, and typically result in a volume decrease. Syntectonic D3 muscovite + quartz + chlorite preferentially grew in an orientation favourable for strain localization, which produced a strong textural softening. Strain localization occurred only where reactions progressed with the infiltration of aqueous fluids, on a scale of hundreds of micrometre. Local fracturing and microseismicity may have induced reactivation of the fault zone and the initial introduction of fluids. However, the predominant greenschist facies deformation (D3) along discrete shear bands was primarily a consequence of the localization of replacement reactions in a partially open system. 相似文献
2.
Proterozoic granulite facies gneisses in MacRobertson Land, east Antarctica, are cut by numerous D5 mylonite-ultramylonite zones of probable Cambrian age. In garnet-absent mafic two-pyroxene gneisses and garnet-bearing charnockitic orthogneisses, the mylonite-ultramylonite zones are characterized by the growth of garnet at the expense of ilmenite, pyroxene and plagioclase. Textures within each mylonite zone can vary from protomylonitic to ultramylonitic. A range of mineral textures involving M5 garnet is developed corresponding to variations in deformation intensity. In protomylonites, garnet occurs as coronas on orthopyroxene-plagioclase and ilmenite-plagioclase boundaries, and as overgrowths on earlier garnet. In ultramylonites, fine-grained orthopyroxene-plagioclase-garnet ± quartz ± clinopyroxene intergrowths and poikilitic garnet are common. Garnet growth in all shear zones is accompanied by shifts in the compositions of neoblastic minerals occurring with garnet, consistent with local chemical equilibrium having been attained during recrystallization. Mylonitization is inferred to have occurred at P ∼ 6.5 kbar. Temperature estimates for M5 vary between 550 and 797 C, which may reflect variations and uncertainties associated with the calibrations used and/or partial re-equilibration during cooling. The presence of post-tectonic, coronate garnet in some mylonite zones indicates that garnet continued to form exclusively in the mylonite zones after movement had ceased and is interpreted to reflect the effects of localized strain heating. 相似文献
3.
金山金矿床成矿时代及矿床成因 总被引：22，自引：0，他引：22
金山金矿床由含金糜棱岩及含金石英脉型矿石组成。矿石的石英流体包裹体Ｒｂ－Ｓｒ等时代年龄测定结果为４０６￣４０９Ｍａ,这两种类型矿石的年龄在测定误差范围内基本一致,属于加里东期成矿。稀土元素分布模式、Ｓ、Ｐｂ及区同位素特征,成矿流体成分资料都说明这两种类型矿石的成矿物质均来自地层,成矿流体属于地层中的建造水及大气降水,矿床应为产于加里东期脆韧剪切带中由改造作用形成的变质细碎屑岩型金矿床。 相似文献
4.
5.
Generation of pseudotachylite under granulite facies conditions, and its preservation during cooling 总被引：1，自引：0，他引：1
Abstract Discontinuous ultramylonite zones cut Proterozoic granulite facies gneisses in MacRobertson Land, east Antarctica, and preserve evidence of ductile non-coaxial flow and reverse sense of shear. Cross-cutting relationships indicate that ultramylonite deformation involved overthrusting to the east, but progressively rotated to involve overthrusting to the north; rotation of the principal compressive stress axes is inferred. Extensive pseudotachylite developed during ultramylonitization, the history of individual ultramylonite zones having involved a single episode of pseudotachylite generation. Neoblastic sillimanite indicates ultramylonitization occurred at >520° C. On the basis of inferred recrystallized granulite facies mineral assemblages ultramylonitization occurred at >700° C, and ≤7.3 ± 0.5 kbar, at aH2O± 0.3 and low aCO2. Comparison of these values with those suggested by metamorphic assemblages in rocks unaffected by mylonitization indicates that the Rayner Complex experienced a late increase in pressure of 1–2 kbar during ultramylonitization. The P-T-aH2O conditions of the ultramylonite zones are inferred to have been close to the solidus for minimum melting, pseudotachylite generation having involved a limited pressure drop during brittle fracturing at high strain rates. Most of the pseudotachylite veins are undeformed; the mechanism(s) of fracturing and melting must have caused strain hardening in rocks surrounding the ultramylonite, further strain having been mostly accommodated by a new or subsidiary shear zone. Renewed stress at reduced strain rates, or renewed stress in zones in which the proportion of pseudotachylite was significantly higher, could have led to the rare occurrences of deformed pseudotachylite. The preservation of fine-grained pseudotachylite is dependent on it remaining dry. 相似文献
6.
7.
花岗质岩石的变形方式和过程决定大陆地壳的流变学特性。本文聚焦藏南拆离系超糜棱岩化的花岗质岩石，借助传统显微构造分析方法和扫描电镜、阴极发光、矿相自动分析系统和电子背散射衍射等新技术手段，开展微观组分、结构、组构定量化观测和分析。超糜棱岩主要造岩矿物为钾长石、斜长石、石英、黑云母等，显微构造呈现为单矿物相域与多相矿物混合域交织结构。相平衡模拟与斜长石钙含量等值线变形温度估算结果为390～410℃。单相域的矿物集合体条带主要分为钾长石条带与石英条带，其中钾长石条带内变形颗粒呈现典型的核 幔构造。组构分析表明钾长石颗粒具有强烈的晶格优选定向，残斑与动态重结晶的钾长石颗粒具有相似的晶格优选方位(CPOs)特征。施密特因子法分析揭示钾长石残斑变形过程中主要活动的滑移系为(100)\[010\]、(010)\[001\]和(001)\[100\]，基质钾长石颗粒形成机制主要为位错蠕变驱动的亚颗粒旋转重结晶。在混合相域，矿物颗粒发生强烈细粒化而只含有少量残斑，基质颗粒主要为斜长石，斜长石颗粒间广泛分布微米级黑云母颗粒。斜长石无组构或弱组构，主导变形机制为颗粒边界滑动。在单相域条带与混合相域基质内，石英颗粒均发生强烈细粒化，颗粒表面发育溶蚀结构以及细小的新晶晶核，石英＜c＞轴晶格优选定向及形态学长轴优选定向皆平行于线理X方向，变形机制为溶解 沉淀蠕变。这显示在由单相域向混合相域的演化过程中，流体作用至关重要，流体与单相域钾长石进行交代使其分解为细粒的斜长石与石英，并导致花岗质岩石变形机制由位错蠕变向非位错蠕变转换，并诱发岩石的流变弱化。 相似文献
8.
北干沟金矿床位于燕山金矿成矿带中段,属含金韧性剪切带石英脉型金矿床.新太古代变质岩含金丰度高,是金成矿的矿源层.韧性剪切带对金矿化具有控制作用.金矿化可分为2期,其与韧性剪切带脆性变形作用有关.自然金主要分布于黄铁矿、黄铜矿及其氧化物的微裂隙、粒间或空洞中.围岩蚀变强烈,主要类型有黄铁矿化、硅化、绢云母化、碳酸盐化、钠长石化、绿泥石化、重晶石化等.矿区今后的主要找矿方向是在I号断裂破碎带中寻找石英脉型、蚀变岩型金矿化和在Ⅱ号韧性剪切带东段的张性扩容段中寻找含金剪切带石英脉型金矿化. 相似文献
9.
10.
金山金矿位于江西省东北部德兴市境内,区域上位于钦杭成矿带东段,属于受韧性剪切带控制的动力变质热液型金矿。研究其成矿时代对其成因及区域找矿等方面具有十分重要的意义,本文在发现金山金矿的赋矿岩石为双桥山群花岗质超糜棱岩的基础上,通过系统的野外地质调查、室内岩矿相学研究,对花岗质超糜棱岩进行了主量元素、微量元素与稀土元素的测试以及LA-ICP-MS U-Pb法测年,探讨了花岗质超糜棱岩原岩形成的构造环境、年代学与区域成矿意义。其SiO2含量介于53.32%~69.86%之间,为中酸性岩。全碱指数（ALK）变化于3.02~6.00,属于亚碱性岩石。铝过饱和指数(A/CNK)变化于0.96~2.49之间,为准铝质和过铝质系列,具S型花岗岩特征。里特曼指数（σ）为0.55~1.62,K2O/Na2O变化于0.48~12.13,为钙碱性和高钾钙碱性系列。富集大离子亲石元素Rb、Th、K、U和La、Ce、Nd、Zr、Hf等,亏损Ba和Ta、Nb、Sr、P、Ti等高场强元素。稀土元素配分曲线为右倾型,重稀土元素部分的曲线形态较为平缓。∑REE=107.64×10-6~168.82×10-6,稀土元素总量偏低。LREE/HREE为5.18~6.44,(La/Yb)N为4.11~6.20,轻重稀土元素分异明显。δEu=0.55~1.00,平均为0.68,具有中等的Eu负异常。锆石中Th/U值介于0.57~2.04,为岩浆成因。金山金矿花岗质超糜棱岩,岩性为花岗闪长岩,属于S型花岗岩,形成于岛弧环境。锆石的LA-ICP-MS定年结果表明其成岩与成矿时代一致,为新元古代（834.3±3.8 Ma）,属晋宁期成矿。本文测试得到其最高金含量可达15.3×10-6,建议重视金山周边地区及整个江南造山带乃至华南其它地区与剪切带有关的新元古界双桥山群火山质变质岩中Au的找矿评价工作。 相似文献