Alleghenian Episode of Basin-Wide Illitization in the Appalachians - A Test of Fluid Expulsion Hypothesis

蒙皂石在成岩和埋藏变质过程中的滑石化作用是页岩岩石学的一个重要方面，K/Ar测年已阐明了这一过程。膨润土简化了研究，因为它们不含碎屑伊利石/蒙皂石。最近的研究表明，整个阿帕契亚盆地南半部的奥陶纪膨润土在相对较短的300-265m.a期间经历了伊利石化成钾(K)-膨润土。早于宾夕法尼亚-下二叠纪，对应于阿勒格尼亚造山带。一些钾膨润土与密西西比河谷型(MVT)锌矿床密切相关。盆地范围的滑石化可能归因于蓝岭逆冲推覆过程中前陆盆地边缘的显露，这一新的假说得到了许多研究人员的不同观察的支持。如果是真的，热水到盆地远端边缘的解释对此类沉积盆地的次级历史具有极其重要的意义，正如Oliver(1986)的推测假说所概述的那样。该项目将对比阿巴拉契亚盆地从南到北的地理分布：(1)阿勒格尼亚造山运动的时间和性质可能是不同的；(2)阿巴拉契亚盆地和伊利诺伊州盆地沿辛辛那提拱顶-纳什维尔穹顶的分界线；(3)沿造山带走向的阿巴拉契亚和瓦奇塔/阿科马盆地之间。最后，阿巴拉契亚页岩中蒙皂石到伊利石反应的岩石学应该与从墨西哥湾沿岸等深埋案例中提出的普遍接受的模式形成鲜明对比，在那里碎屑钾长石的化学分解起着主要作用。

The illitization of smectite during diagenesis and burial metamorphism is a major aspect of shale petrology; K/Ar dating has elucidated the process. Bentonites simplify the study because they are free of detrital illite/smectite. Recent research shows that Ordovician bentonites throughout the southern half of the Applachian basin underwent illitization to potassium (K)- bentonites during a relatively short episode 300-265 m.y. ago in the upper Pennslyvania- lower Permian, corresponding to the Alleghenian Orogeny. Some of the K-bentonites are in close association with Mississippi Valley Type (MVT) zinc deposits. Basin-wide illitization may be attributed to explusion of edge of the foreland basin during Blue Ridge overthrusting, a novel hypothesis that is receiving support from diverse observations by many researchers. If true, the explusion of hot waters to the distal edges of the basin as of mega-importance to the secondary history of such sedimentary basins, as outlined in the speculative hypothesis by Oliver (1986). This project will contrast the geographic distribution of illitization dates (1) within the Appalachian Basin from south to north, where the timing and character of the Alleghenian Orogeny may have been different; (2) between the Appalachian Basin and Illinois Basin along their divide at the Cincinnati Arch-Nashville Dome; and (3) between the Appalachian and Ouachita/Arkoma Basins along the strike of the orogen. Finally the petrology of the smectite to illite reaction in Appalachian shales should provide a marked contrast with the generally accepted model proposed from deeply buried cases like the Gulf Coast, where the chemical breakdown of detrital K-feldspar plays a major role.