共查询到19条相似文献，搜索用时 187 毫秒
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四川盆地东南部早三叠世地震事件沉积及其地质意义 总被引：1，自引：0，他引：1
四川盆地南部及东南部下三叠统飞仙关组和嘉陵江组中常发育有一系列宏观及微观的软沉积物变形、震积角砾岩块、板状砾屑、层内微断层等特殊的地震成因沉积构造。飞仙关组震积岩在重庆北碚白庙子剖面飞仙关组第一、二段中产出,嘉陵江组震积岩产于四川叙永龙洞湾嘉陵江组第二段及四川兴文、贵州习水等地的相同层位中,其沉积序列明显,反映了古地震从开始至平静的全过程。作者认为,早三叠世时,上扬子板块西缘以川西义敦弧的演化为代表的三江构造带活动强烈,可能与四川盆地早三叠世震积岩的形成有联系,随着三江构造带板块碰撞、洋壳俯冲消减,能在较大区域内引发地震活动、火山喷发。 相似文献
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豫南桐柏—信阳一带分布着一条为许多构造位移面所分割的岩带。据目前资料看它是由不同时代、不同来源的岩石、岩层碎块相互呈混杂状态的混杂岩带,即桐柏—信阳混杂岩带。它标志着华南、华北两板块地缝合线所在部位。其两侧分别发育有以片岩、片麻岩、斜长角闪岩、大理岩为主,组成的信阳群和毛集群、围山城群等,它们分别代表此两板块中元古代至晚古生代期间,活动性大陆边缘的沉积。 桐柏—信阳混杂岩带主要分布在NWW向的桐—商断裂带内,向西延至南阳盆地,其东端经商城北,尚有继续延伸入皖北的趋势,长达200公里以上。 相似文献
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沿雅鲁藏布江缝合带的蛇绿岩套出露状态可分为3种类型,如在岗仁波齐和白朗地区完整出露大套基性 超基性岩体,层状堆晶岩,辉绿岩质岩席、岩墙,以及层状深海沉积建造。而在仁布地区的蛇绿岩露头规模迅速收敛,仅剩少量地幔岩体表现为串珠状排列的小岩株向东延伸并逐渐尖灭。在拉萨地区蛇绿岩套则完全缺失,相应位置出露一套同时代中 酸性火山岩建造。为探讨雅鲁藏布江蛇绿岩带的大地构造性质,笔者选择蛇绿岩套出露巨厚、迅速收敛和完全缺失3种不同的构造位置开展构造-沉积剖面研究。初步结果显示：白朗大规模蛇绿岩套核心区保留基底构造窗,且局部可直接观察到深海沉积建造与上下围岩复理石的沉积整合接触关系。仁布地区的镁铁 超镁铁岩体具有保留完好的原生侵位构造形迹,岩体与围岩常呈侵位时的牵引平行或者低角度斜交接触关系,地幔岩与围岩接触带保留典型烘烤边等热接触变质带（晕）等。两剖面的岩石均处于区域性脆性 韧脆性变形和低绿片岩相变质作用,缺乏统一的区域性构造极性,因而整体属于原地系统,并非经历板块俯冲-碰撞-反逆冲的外来残余洋壳岩片。拉萨地区在蛇绿岩带向东延线位置出露侏罗-白垩系中 酸性火山建造,大剖面南北两侧的中 新生代沉积建造的岩性组合,构造样式和沉积环境演变过程具有明显的相似性和时间上的宏观对应性,应当记录了同一个盆地的完整演化旋回。上述构造-沉积地质特征说明雅鲁藏布江蛇绿岩套并不代表中生代近万公里宽阔洋壳的残余构造岩片,新特提斯洋实际上属于一条中生代不均一洋壳化的弧后裂陷盆地。 相似文献
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Dov Bahat 《Australian Journal of Earth Sciences》2013,60(1):93-102
In ternary feldspars of essentially one phase, calcium content has a dominant influence on the optic axial angle. In such feldspars and also in binary feldspars from solvsbergite rocks, variations of cooling histories do not significantly affect the optic axial angle. In ternary feldspars which are unmixed into two or three prominent phases, Al/Si ordering has an important effect on the 2V value. A recent suggestion of several writers that in feldspars the alkali structural site may be partially occupied by (H3O)+ ions is applied as a possible way to explain a correlation observed between petrographical features of the rocks and the optic axial angles of their feldspar phenocrysts. 相似文献
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Behavior and effects of phosphorus in the system Na2O−K2O−Al2O3−SiO2−P2O5−H2O at 200 MPa(H2O) 总被引：1，自引：1，他引：1
David London George B. Morgan VI Harold A. Babb Jennifer L. Loomis 《Contributions to Mineralogy and Petrology》1993,113(4):450-465
The addition of phosphorus to H2O-saturated and initially subaluminous haplogranitic (Qz–Ab–Or) compositions at 200 MPa(H2O) promotes expansion of the liquidus field of quartz, a marked decrease of the solidus temperature, increased solubility limits of H2O in melt at low phosphorus concentrations, and fractionation of melt out of the haplogranite plane (projected along an Or28 isopleth) toward a peralkaline, silica-poor but quartz-saturated minimum composition. The partition coefficient for P2O5 between aqueous vapor and melt with an ASI (aluminum saturation index, mol Al/[mol Na+K])=1 is negligible (0.06), and consequently so are the effects of phosphorus on other melt-vapor relations involving major components. Phosphorus becomes more soluble in vapor, however, as the concentration of a NaPO3 component increases via the fractionation of melt by crystallization of quartz and feldspar. The experimental results here corroborate existing concepts regarding the interaction of phosphorus with alkali aluminosilicate melt: phosphorus has an affinity for alkalis and Al, but not Si. Phosphorus is incorporated into alkali feldspars by the exchange component AlPSi-2. For subaluminous compositions (ASI=1), the distribution coefficient of phosphorus between alkali feldspar and melt, D[P]Af/m, is 0.3. This value increases to D[P]Af/m=1.0 at a melt ASI value of 1.3. The increase in D[P]Af/m with ASI is expected from the fact that excess Al promotes the AlPSi-2 exchange. With this experimental data, the P2O5 content of feldspars and whole rocks can reveal important facets of crystallization and phosphorus geochemistry in subaluminous to peraluminous granitic systems. 相似文献
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The bulk compositions of the groundmass alkali feldspar from the Hell Canyon Pluton is 0.146mole% albite. The composition of the outermost zone of the oscillatory zoned plagioclase is 0.686 mole% albite, whereas the most calcic cores have a composition of 0.43 mole% albite. The structural state of the alkali feldspar is near orthoclase. Both composition of coexisting feldspars and structural state of the alkali feldspar are nearly constant throughout the pluton.Exsolved albite in the alkali feldspar have a composition of 0.965 mole% albite and the orthoclase host has a composition of 0.032 mole%. Singe crystal X-ray studies indicate that the albite intergrowths are coherent with the host.Equilibrium temperatures derived from the coexisting feldspar average 554 ° C; about 150 ° C, too low for the minimum solidus temperatures for reasonable emplacement pressures (2 kb). If this minimum solidus temperature is assumed, then the alkali feldspar has lost about 0.15 mole% albite. This loss was most likely caused by hydrothermal solutions associated with the crystallizing magma and equilibrated at about 550 ° C. However, based on the coherent albite intergrowths and the orthoclase structure state it can be inferred that the system was relatively free of volatiles below 500 ° C. Final equilibirium between orthoclase host and albite intergrowths occurred at about 311 ° C. 相似文献
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《Chemie der Erde / Geochemistry》2021,81(2):125730
The Ghansura Rhyolite Dome of the Bathani volcano-sedimentary sequence in eastern India originated from a subvolcanic felsic magma chamber that was intruded by volatile-rich basaltic magma during its evolution leading to the formation of a porphyritic andesite. The porphyritic andesite consists of rapakivi feldspars, which are characterized by phenocrysts of alkali feldspar mantled by plagioclase rims. Results presented in this work suggest that intimate mixing of the mafic and felsic magmas produced a homogeneous hybrid magma of intermediate composition. The mixing of the hot volatile-rich mafic magma with the relatively colder felsic magma halted undercooling in the subvolcanic felsic system and produced a hybrid magma rich in volatiles. Under such conditions, selective crystals in the hybrid magma underwent textural coarsening or Ostwald ripening. Rapid crystallization of anhydrous phases, like feldspars, increased the melt water content in the hybrid magma. Eventually, volatile saturation in the hybrid magma was reached that led to the sudden release of volatiles. The sudden release of volatiles or devolatilization event led to resorption of alkali feldspar phenocrysts and stabilizing plagioclase, some of which precipitated around the resorbed phenocrysts to produce rapakivi feldspars. 相似文献
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二长石地质温度计在估算乌拉山金矿碱性长石形成温度中的应用 总被引：1，自引：0，他引：1
内蒙古乌拉山金矿田内主要出露晚太古代乌拉山群区域变质岩和规模不一的花岗岩体以及不同时代、不同种类的脉状地质体。含金矿脉中主要矿物共生组合为碱性长石、石英、斜长石、碳酸盐矿物(方解石、白云石)和少量金属硫化物。矿床的显著特征为碱性长石交代作用强烈，碱性长石也广泛产于该地区其他各种类型的岩石中。本文采用电子显微探针分析了共生碱性长石和斜长石的化学成分，并采用三元二长石温度模型估计了碱性长石的平衡温度。结果表明，第一成矿阶段的碱性长石一石英含金矿脉中碱性长石的形成温度为353℃，第二成矿阶段石英含金矿脉中碱性长石的形成温度为281℃，矿脉碱性长石形成压力约为5kbar。这些结果与同类矿石中平衡共生的碳酸盐矿物和云母类矿物的地质温度计估计的形成温度以及共生石英中流体包裹体的均一温度非常一致。因此，乌拉山金矿床形成和富集的温度可估测为260～380℃，压力约为5kbar。此外，应用二长石温度计计算了本地区区域变质片麻岩和花岗岩中碱性长石的平衡温度，所得温度比采用共生铁铝榴石和黑云母温度计估计的温度要低约250℃。这表明共生的铁铝榴石和黑云母的平衡温度可能代表其寄主变质岩变质期温度及寄主花岗岩原生温度，而区域变质岩和花岗岩中的碱性长石在经历了随后多次热液作用后，可能重新平衡再生，这也与前人对乌拉山金矿的矿床地质和同位素研究的结果一致。 相似文献
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Robert O Fournier 《Geochimica et cosmochimica acta》1976,40(12):1553-1561
In order to determine whether gas (steam) containing a small amount of dissolved alkali chloride is effective in promoting base exchange of Na+ and K+ among alkali feldspars and coexisting brine or brine plus solid salt, experiments were carried out at 400–700°C and steam densities ranging down to less than 0.05. For bulk compositions rich in potassium, the low pressure results are close to previous high-pressure results in composition of the fluid and coexisting solid phase. However, when the bulk composition is more sodic, alkali feldspars are relatively richer in potassium at low pressure than at high pressure. This behaviour corresponds to enrichment of potassium in the gas phase relative to coexisting brine and precipitation of solid NaCl when the brine plus gas composition becomes moderately sodic.
The gas phase is very effective in promoting base exchange between coexisting alkali feldspars at high temperature and low water pressure. This suggests that those igneous rocks which contain coexisting alkali feldspars out of chemical equilibrium either remained very dry during the high-temperature part of their cooling history or that the pore fluid was a gas containing very little potassium relative to sodium. 相似文献
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STRESS-METAMORPHISM AND ISOTOPIC AGE OF SHEAR ZONE GRANITOID TECTONITES OF IRTYSH SHEAR ZONE (ALTAI REGION) 总被引：1，自引：0，他引：1
B.M.Chikov V.A.Ponomachuk S.V.Zinoviev B.N.Lapin A.T.Titov A.V.Travin S.V.Palessky 《大地构造与成矿学(英文版)》2002,26(1):36-51
The Irtysh shear zone (ISZ) of Altai region is the lineament structure of the collision-suture type, where granites of Kalba complex and granodiorites of Zmeinogorsk complex are exposed to regional gneiss-formation and stress-metamorphic alterations. This study is based on detailed structural observations at special grounds using optical and electron microscopy, and on the behavior analysis of isotopic systems from altered granitoids.Within the ISZ area we have established the continuous rows of granitoid stress-metamorphism from initial recrystallization of protolite, its cataclasis and mechanical flaring up to complete recrystallization with alteration of mineral composition and formation of the streaky complexes of granite tectonites of blastomylonite and blastocataclasite types. The directed alteration of rocks has several impulse and is expressed by a change in morphology of mineral grains and their relations, magnification of deformation component in the rock structure, and formation of new mineral phases on the basis of initial ones without surface fluidization. At transformation of isotopic systems from granitoid, their feldspars,biotite and hornblende, we can observe “rejuvenation“ of the rock substrate from 270- 290 Ma for Kalba granitoids to 220-235 Ma for their tectonites, and for Rudny Altai granodiorites, their ages changes from 285-317 Ma to 232-257 Ma for their tectonites. 相似文献