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首页> 外文期刊>Contributions to Mineralogy and Petrology >Diffusion-controlled biotite breakdown reaction textures at the solid/liquid transition in the continental crust
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Diffusion-controlled biotite breakdown reaction textures at the solid/liquid transition in the continental crust

机译：大陆壳固液过渡过程中扩散控制的黑云母分解反应织构

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Two-phase quartz intergrowths with garnet, cordierite and tourmaline occur commonly in prograde high-temperature migmatites, granulites, as well as in the last crystallization stages of biotite granites. Structural, microtextural and mineralogical data show that they result from the breakdown of biotite in the presence of a melt phase associated with incongruent dissolution of feldspars into the melt and silica release (giving quartz in silica saturated rocks). Biotite breakdown and growth of Al-rich ferromagnesian minerals, occurring at the solid–liquid transition in the crust (early melting or final crystallization), is kinetically controlled by Fe and Mg mass transport, the network-forming cations Si and Al being locally compensated for by feldspar dissolution/crystallization. This process leads to significant changes with respect to equilibrium dehydration-melting reactions wherein quartz is a reactant and K-feldspar a reaction product. Therefore, quartz inclusions commonly occurring in garnets from granulite-facies metapelites and metagraywackes are not simply grains passively included during garnet growth. They may also correspond to newly crystallized phases. Resorption of feldspar may lead to more alkaline melt and to crystalline residue richer in Al than expected under equilibrium conditions. Hence, excess alumina in granulite-facies rocks is not necessarily related to initial alumina-rich whole-rock compositions (as currently considered), but may be due, at least partly, to kinetics of melting.
机译：石榴石，堇青石和电气石与石英的两相共生通常发生在高级高温辉石，花岗石以及黑云母花岗岩的最后结晶阶段。结构，微观结构和矿物学数据表明，它们是由于黑云母在熔融相的存在下分解而造成的，该相与长石不适当地溶解到熔融物中并释放出二氧化硅有关（在饱和石英岩中产生石英）。富铝镁铁矿矿物的黑云母分解和生长发生在地壳的固液过渡期（早期熔融或最终结晶），受铁和镁的质量传输动力学控制，形成网络的阳离子Si和Al被局部补偿通过长石溶解/结晶。该过程导致平衡脱水熔融反应的显着变化，其中石英是反应物，钾长石是反应产物。因此，通常在石榴石中的粒状相变质岩和变灰质ack石中普遍存在石英夹杂物，而不仅仅是石榴石生长过程中被动包含的晶粒。它们也可以对应于新结晶的相。长石的吸收可能导致更多的碱性熔体和比平衡条件下预期的富含Al的晶体残留物。因此，花岗石相岩石中过量的氧化铝不一定与初始富氧化铝全岩石成分（目前认为）有关，而可能至少部分是由于熔融动力学所致。

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