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K. BUCHER-NURMINEN 《Journal of Metamorphic Geology》1988,6(6):667-672
Abstract The textural and compositional features of phlogopites in a contact-metamorphic dolomite marble inclusion in the Bergell intrusion (central Alps) and in a metasomatic reaction vein cutting through this marble suggest different origins for vein phlogopites:
(a) High-Al vein phlogopite represents former marble phlogopite which has been compositionally modified by reaction with the vein forming fluid.
(b) Low-Al vein phlogopite represents phlogopite precipitated from the vein forming fluid.
As both types of vein phlogopite were in contact with the same vein forming fluid at the same time, low-Al phlogopite most likely represents an equilibrium phlogopite composition, whereas high-Al phlogopite does not. High-Al vein phlogopite retained its Al-content from the contact-metamorphic marble parent phlogopite and only underwent Fe-Mg exchange with the metasomatic fluid.
All the vein phlogopites studied are strongly enriched in Fe relative to marble phlogopite. The data may suggest in general that phlogopite Al/Si ratios may be retained from the conditions under which the phlogopites first formed, whereas the Mg/Fe-ratios may be substantially modified by exchange with other ferromagnesian solid phases and/or a metamorphic fluid at later stages in their metamorphic history. This may have significant effects on calculated pressures and temperatures from thermobarometers involving biotite. 相似文献
(a) High-Al vein phlogopite represents former marble phlogopite which has been compositionally modified by reaction with the vein forming fluid.
(b) Low-Al vein phlogopite represents phlogopite precipitated from the vein forming fluid.
As both types of vein phlogopite were in contact with the same vein forming fluid at the same time, low-Al phlogopite most likely represents an equilibrium phlogopite composition, whereas high-Al phlogopite does not. High-Al vein phlogopite retained its Al-content from the contact-metamorphic marble parent phlogopite and only underwent Fe-Mg exchange with the metasomatic fluid.
All the vein phlogopites studied are strongly enriched in Fe relative to marble phlogopite. The data may suggest in general that phlogopite Al/Si ratios may be retained from the conditions under which the phlogopites first formed, whereas the Mg/Fe-ratios may be substantially modified by exchange with other ferromagnesian solid phases and/or a metamorphic fluid at later stages in their metamorphic history. This may have significant effects on calculated pressures and temperatures from thermobarometers involving biotite. 相似文献
646.
Granulite facies magnesian metapelites commonly preserve a wide array of mineral assemblages and reaction textures that are useful for deciphering the metamorphic evolution of a terrane. Quantitative pressure, temperature and bulk composition constraints on the development and preservation of characteristic peak granulite facies mineral assemblages such as orthopyroxene + sillimanite + quartz are assessed with reference to calculated phase diagrams. In NCKFMASH and its chemical subsystems, peak assemblages form mainly in high‐variance fields, and most mineral assemblage changes reflect multivariant equilibria. The rarity of orthopyroxene–sillimanite–quartz‐bearing assemblages in granulite facies rocks reflects the need for bulk rock XMg of greater than approximately 0.60–0.65, with pressures and temperatures exceeding c. 8 kbar and 850 °C, respectively. Cordierite coronas mantling peak minerals such as orthopyroxene, sillimanite and quartz have historically been used to infer isothermal decompression P–T paths in ultrahigh‐temperature granulite facies terranes. However, a potentially wide range of P–T paths from a given peak metamorphic condition facilitate retrograde cordierite growth after orthopyroxene + sillimanite + quartz, indicating that an individual mineral reaction texture is unable to uniquely define a P–T vector. Therefore, the interpretation of P–T paths in high‐grade rocks as isothermal decompression or isobaric cooling may be overly simplistic. Integration of quantitative data from different mineral reaction textures in rocks with varying bulk composition will provide the strongest constraints on a P–T path, and in turn on tectonic models derived from these paths. 相似文献
647.
在大石桥地区进行1:50000地质填图过程中,经过大量的岩石薄片观察,在江河岩群变泥质岩石中,首次发现了红柱石转变为蓝晶石和十字石转变为蓝青石的变质反应.详细的岩相学、岩石化学及矿物化学的研究表明,变泥质岩中先后发生的这两种变质反应,代表了本区变质作用演化的两个重要阶段.揭示了本区在伸展体制下地壳拉伸、减薄和收缩体制下的褶叠、推覆及之后的抗返、抬升的地球动力学过程. 相似文献
648.
递增变质带广泛出露于全球元古代至新生代的众多造山带中,但递增变质作用的成因尚不完全清楚。本文归纳了典型递增变质带的研究成果,讨论了如下几个悬而未决的科学问题:递增变质带的热源、变质反应与变质作用P- T- t轨迹特征、流体来源与作用、变质与变形耦合关系、花岗岩及混合岩化作用、递增变质带的折返/隆升机制,以及递增变质作用的构造成因等。本文综述了上述科学问题研究进展,探讨了递增变质作用的可能成因。 相似文献
649.
Chemical reactions of plagioclase, biotite and their singleminerals, as well as a mineral mixture of (plagioclase +biotite+quartz), with KCl and (KCl+KHCO3) solutions were carried out at 150400℃ and 5080 MPa. Experiments show that alkaline fluid promotes plagioclase’s changing into potash feldspar, while acid fluid helps plagioclase, potash feldspar and biotite alteration form chlorite and sericite. After chemical reaction the acidity-alkalinity of solutions often changes reversely. It was observed that gold dissolved from the tube wall and recrystallized on the surfaces of biotite and pyrite. Therefore the transportation and enrichment of gold are related to the elementary effect of the fluid-mineral interfaces. Fe3+-Fe2+, as an oxidition-reduction agent, and volatile components Cl? and CO2 play important roles in the reaction process. 相似文献
650.
剪切应力作用下晶质矿物的化学行为及其地质意义 总被引:2,自引:0,他引:2
地壳中晶质矿物的化学行为主要为溶解、固相-固相反应和表面化学行为3类,剪切应力作用可以加速和促进这3类行为。其原因主要在于剪切应力作用可以改变矿物的晶格结构,增加其内部和表面缺陷。 相似文献