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

蒙脱石在成岩作用和埋藏变质作用中的illi石化作用是页岩岩石学的一个重要方面；K/Ar测年已经阐明了这一过程。膨润土简化了研究，因为它们不含伊利石/蒙脱石碎屑。最近的研究表明，阿帕契亚盆地南半部的奥陶系膨润土在距今300-265万年的上宾夕法尼亚—下二叠世（与阿勒格尼期造山运动相对应）一个相对较短的时期内经历了钾(K)膨润土的illitization。某些钾型膨润土与密西西比河谷型（MVT）锌矿床密切相关。蓝岭逆冲过程中前陆盆地边缘的喷发可能导致了全盆地的非石化化，这一新的假设得到了许多研究者的不同观测结果的支持。如果这是真的，那么就像Oliver（1986）在推测性假设中所概述的那样，热水向盆地远端边缘的喷发对此类沉积盆地的次要历史具有极其重要的意义。该项目将对比阿巴拉契亚盆地从南到北的illiization日期(1)的地理分布，阿勒格尼期造山运动的时间和特征可能有所不同；(2)在阿巴拉契亚盆地和伊利诺伊盆地之间，沿着辛辛那提拱门-纳什维尔圆顶的分界线；(3)沿造山带走向的阿巴拉契亚盆地和瓦希塔/阿科马盆地之间。最后，阿巴拉契亚页岩中蒙脱石到伊利石反应的岩石学应该与墨西哥湾沿岸等深埋地区提出的普遍接受的模式形成鲜明对比，在墨西哥湾沿岸，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.