Reliability of very low-grade metamorphic methods to decipher basin evolution: Case study from the Markstein basin (Southern Vosges, NE France)
Reliability of very low-grade metamorphic methods to decipher basin evolution: Case study from the Markstein basin (Southern Vosges, NE France)
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DOI：
10.1016/j.clay.2016.10.003
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发表时间：
2016-12
影响因子：
5.6
通讯作者：
S. Potel;Tatiana Maison;M. Maillet;A. Sarr;M. Doublier;G. Trullenque;R. F. Mählmann
中科院分区：
文献类型：
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作者：
S. Potel;Tatiana Maison;M. Maillet;A. Sarr;M. Doublier;G. Trullenque;R. F. Mählmann
研究粘土矿物的蚀变和反应进程的低级和极低级变质研究是破译沉积盆地和倒转变质沉积盆地热演化的有力工具。片状硅酸盐如伊利石和绿泥石在沉积盆地层序中非常常见。它们可用于确定通过 XRD 测量的成岩作用和低温变质作用的等级：分别为伊利石 Kübler 指数（KI；旧文献中的伊利石“结晶度”）和绿泥石 Árkai 指数（ÁI；旧文献中的绿泥石“结晶度”）。尽管 ÁI 方法被认为比 KI 方法灵敏度稍低，但在具有均匀热流历史和较小构造构造复杂性的变质域中经常观察到两种方法之间的可靠相关性。作为对这些方法的补充，K-white micabcell 维度提供了对极低至低温度域中达到的压力相的可靠估计。在这里，我们介绍了位于孚日山脉南部马克斯坦盆地的案例研究。盆地岩石地层单元的特征分别为上泥盆统至上维西安时代的深海复理石序列和火山碎屑沉积物。马克斯坦盆地周围环绕着侵入年龄在 340 至 326 Ma 之间的花岗岩。先前的一项研究表明，造山变形以区域褶皱为特征，并且在距离接触点长达 1500 米的花岗岩外晕中发现了接触变质作用（由黑云母的出现所界定）。在这里，我们提出了一项结合矿物组合、伊利石和绿泥石“结晶度指数”以及 K-white micabcell 尺寸的多学科研究。我们的方法允许（i）详细绘制区域/埋藏变质和接触变质域的面积范围； (ii) 揭示两个区域内的变质带； (iii) 更好地限制区域/埋藏和接触变质历史。接触变质域的特征是黑云母和/或阳起石的出现以及低 K-白细胞尺寸，而早期造山变质作用区域则产生具有中等 K-白细胞尺寸的高级成岩作用和安奇带的 KI 和 ÁI 值。
Low- and very low-grade metamorphic studies investigating the alteration and reaction progress of clay minerals are powerful tools to decipher the thermal evolution of sedimentary and inverted meta-sedimentary basins. Sheet silicates such as illite and chlorite are very common in sedimentary basin sequences. They can be used to determine the grade of diagenesis and low-temperature metamorphism as measured through the XRD: illite Kübler-Index (KI; illite “crystallinity” in older literature) and the chlorite Árkai-Index (ÁI; chlorite “crystallinity” in older literature), respectively. Although the ÁI method is considered to be slightly less sensitive than the KI method, a reliable correlation between both methods is often observed in metamorphic domains with a uniform heat-flow history and minor tectono-structural complexity. Complementary to these methods, the K-white micabcell dimension provides a robust estimate of pressure facies reached in very low- to low-grade temperature domains.Here, we present a case-study from the Markstein basin located in the Southern Vosges. The lithostratigraphic units in the basin are characterized by deep marine flysch sequences of Upper Devonian to Upper Visean age and volcano-clastic sediments, respectively. The Markstein basin is surrounded by granitoids with intrusion ages between 340 and 326 Ma. A previous study showed orogenic deformation characterized by regional folding, and a contact metamorphism found in an outer halo of the granitoids up to 1500 m away from the contact (delineated by the occurrence of biotite). Here we present a multi-disciplinary study combining mineral assemblages, illite and chlorite “crystallinity indices”, and K-white micabcell dimension. Our approach allows to (i) map in (great) detail the areal extent of both regional/burial metamorphic and contact metamorphic domains; (ii) reveal the metamorphic zonation within both domains; and (iii) better constrain regional/burial and contact metamorphic history. The contact metamorphic domain is characterized by the occurrence of biotite and/or actinolite and low K-white micabcell dimensions, whereas the zone of incipient orogenic metamorphism yields KI and ÁI values of the high-grade diagenesis and anchizone with intermediate K-whitebcell dimensions.