Recrystallization of high-pressure marble (Sivrihisar, Turkey)
Recrystallization of high-pressure marble (Sivrihisar, Turkey)
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DOI：
10.1016/j.tecto.2009.08.015
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发表时间：
2009-12
期刊：
影响因子：
2.9
通讯作者：
N. Seaton;D. Whitney;C. Teyssier;E. Toraman;M. Heizler
中科院分区：
文献类型：
--
作者：
N. Seaton;D. Whitney;C. Teyssier;E. Toraman;M. Heizler
在土耳其的 Sivrihisar 地块，蓝片岩相地体的南缘受到与后来的区域（巴罗维）变质作用相关的加热和变形的影响，形成了可以在方解石微观结构中观察到的重结晶前沿。方解石大理岩记录了从北部地区的高压（HP）结构到南部地区的完全再结晶（绿片岩到角闪岩相）结构的演变，其中包括高压结构的部分再结晶的中间阶段。 HP大理石的特点是棒状方解石（文石假晶）排列成串，每个颗粒的长轴倾斜于成分层；倾斜度从 50° 到接近平行不等，但大角度最为常见。在包含部分退化蓝片岩和榴辉岩的狭窄（约 200m 厚）过渡带中，HP 纹理部分被小而等量的重结晶颗粒链覆盖，这些颗粒保留了先前存在的棒状方解石的晶体取向，如电子背散射衍射分析所示；局部出现棒状晶体。在过渡区以南约 100 m 厚的区域中，所有方解石颗粒均等，但具有晶体择优取向。在巴罗夫序列的更南边，重结晶大理石含有随机取向的等量方解石。两个域的织物元素（叶理、线理）的相似性进一步显示了巴罗维相关过程对 HP 域的影响，包括沿叶理平面剪切期间方解石棒的旋转。高压大理岩中白云母的白云母40Ar/39Ar年龄为~88Ma，巴罗维亚大理岩中白云母的白云母年龄为~59Ma，表明高压岩石的初始折返和冷却与后期变质事件中变形和加热的岩石的最终冷却之间的时间间隔为~30Ma。
In the Sivrihisar Massif, Turkey, the southern margin of a blueschist facies terrane was affected by heating and deformation associated with later regional (Barrovian) metamorphism, creating a recrystallization front that can be observed in calcite microstructures. Calcite marble records a progression from high-pressure (HP) textures in a northern domain to completely recrystallized (greenschist to amphibolite facies) textures in a southern domain, with intermediate stages of partial recrystallization of the HP textures. HP marble is characterized by rod-shaped calcite (aragonite pseudomorphs) arranged in series with the long axis of each grain oblique to compositional layering; obliquity varies from 50° to nearly parallel, but high angles are most common. In a narrow (~200m thick) transition zone that contains partially retrogressed blueschist and eclogite, the HP texture is partially overprinted by chains of small, equant, recrystallized grains that preserve the crystallographic orientation of the pre-existing rod-shaped calcite, as revealed by electron backscatter diffraction analysis; rod-shaped crystals occur locally. In a ~100m thick zone south of the transition zone, all calcite grains are equant but have a crystallographic preferred orientation. Further south in the Barrovian sequence, recrystallized marble contains equant calcite that is randomly oriented. The similarity in fabric elements (foliation, lineation) of the two domains further shows the effect of Barrovian-related processes on the HP domain, including the rotation of the calcite rods during shearing along foliation planes. White mica40Ar/39Ar ages for phengite in HP marble are ~88Ma, and for muscovite in Barrovian marble are ~59Ma, indicating ~30Ma time interval between initial exhumation and cooling of the HP rocks and final cooling of the rocks that were deformed and heated during the later metamorphic event.