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Regularly Interstratified Chlorite/Vermiculite in Contact Metamorphosed Red Beds, Newark Group, Connecticut Valley

Published online by Cambridge University Press:  01 July 2024

Richard H. April
Richard H. April*
Affiliation:
Department of Geology, Colgate University, Hamilton, New York 13346
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Abstract

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A regularly interstratified chlorite/vermiculite occurs in red beds of the East Berlin Formation (Early Jurassic age) in the Connecticut Valley. The mineral is restricted to a 2.5-m wide zone of contact metamorphosed strata adjacent to and underlying the Hampden Basalt. Chemical and X-ray powder diffraction data indicate that the chlorite/vermiculite formed in response to lava-induced elevated temperatures and the availability of magnesium in the muds during and shortly after emplacement of the lava flow. Near the contact, hydrothermal fluids originating from the lava and from the synchronal weathering of basalt fragments by superheated pore waters provided a source of Mg. Further from the contact, magnesium was primarily derived from the thermal dissociation of dolomite. K2O concentrations and the distribution of clay minerals in the red mudstone suggest that the interstratified chlorite/vermiculite formed from preexisting illite or vermiculite as potassium was released and brucitic sheets were incorporated into interlayer positions.

Резюме

Резюме

Обычно переслаивающийся хлорит-вермикулит встречается в красных слоях формации Восточный Берлин (ранняя Юра) в Коннектикутской Долине. Этот минерал находится только в зоне контактного метаморфизма шириной 2,5 мили в отложениях, прилегающих к Базальту Хампден и подстилающих его. Химические анализы и данные порошкового метода рентгено-структурного анализа показывают, что хлорит-вермикулит образовался в результате повышенных температур, вызванных лавой, и присутствия магния в грязях во время и сразу после соприкосновения с потоком лавы. Около контакта гидротермальные жидкости, образующиеся в лаве и в результате одновременного выветривания базальтовых обломков перегретыми поровымн водами, служили источником магния. Дальше от контакта магний высвобождался в основном в результате термальной диссосиации доломита. Концентрации K2O и распределение глинистых минералов в красном аргиллите позволяют заключить, что переслаивающийся хлорит-вермикулит образовался из существующего уже иллита или вермикулита при высвобождении калия и включении бруситовых листов в межслойное пространство. [N. R.]

Resümee

Resümee

Eine regelmäßige Chlorit-Vermiculit Wechsellagerung kommt in den Rotschichten der East Berlin Formation (frühjurassisches Alter) im Connecticut Valley vor. Das Mineral ist auf eine 2,5 m breite kontaktmetamorphe Schicht beschränkt, die unmittelbar unter dem Hampden Basalt liegt. Chemische und Röntgendiffraktometer-Daten deuten darauf hin, daß die Chlorit-Vermiculit Wechsellagerung gebildet wurde, weil bedingt durch die Lava die Temperaturen erhöht waren, und im Schlick Magnesium während und kurz nach der Platznahme des Lavastroms zur Verfügung stand. Nahe dem Kontakt wurde Magnesium von hydrothermalen Lösungen geliefert, die von der Lava selbst stammen und die bei der gleichzeitig stattfindenden Veränderung von Basaltbruchstücken durch überhitzte Porenwässer entstehen. Weiter vom Kontakt entfernt stammt das Magnesium vor allem von der thermischen Dissoziation von Dolomit. Die K2O-Konzentrationen und die Tonmineralverteilung in den Rotschichten deuten darauf hin, daß die Chlorit-Vermiculit Wechsellagerung aus Illit oder Vermiculit gebildet wurden, indem Kalium herausgelöst wurde, und Brucitschichten in die Zwischenschichtpositionen eingebaut wurden. [U. W.]

Résumé

Résumé

Une chlorite-vermiculite régulièrement interstratifiée est trouvée dans les lits rouges de la East Berlin Formation (d’âge bas-Jurassique) dans la vallée du Connecticut. Le minéral est restreint à une zone de 2,5 m de largeur de couches métamorphosées au contact adjacentes à et sous le Hampden Basalt. Les données chimiques et de diffraction aux rayons-X indiquent que la chlorite-vermiculite a été formée en réponse à des températures élevées dues à la lave et à la présence de magnésium dans les boves pendant et peu après l'emplacement du flot de lave. Près du lieu de contact, les fluides hydrothermaux originant de la lave et de l'altération synchronique de fragments de basait par des eaux aux pores fortement échauffées ont fourni une souree de magnésium. Aux endroits plus éloignes du lieu de contact, le magnesium a été principalement dérivé de la dissociation thermale de dolomite. Les concentrations de K2O et la distribution de minéraux argileux dans les rouches argileuses rouges suggèrent que la chlorite-vermiculite a été formèe â partir d'illite ou de vermiculite pré-existante alors que le potassium était relâché et des couches brucitiques étaient incorporées dans des positions interfeuillet. [D. J.]

Keywords

ChloriteContact metamorphismHydrothermalMixed-layerRed bedsVermiculite
Type
Research Article
Information
Clays and Clay Minerals , Volume 28 , Issue 1 , February 1980 , pp. 1 - 11
Copyright
Copyright © Clay Minerals Society 1980

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