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Clay Mineral Formation in an Alpine Environment

Published online by Cambridge University Press:  01 July 2024

Robert C. Reynolds Jr.*
Affiliation:
Earth Sciences Department, Dartmouth College, Hanover, N.H. 03755, U.S.A.
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Abstract

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Vermiculite, mixed-layer vermiculite-phlogopite, and smectite are presently forming from igneous and metamorphic bedrock in the alpine zone of the northern Cascades, Washington. In addition, south-facing exposures of quartz-diorites and metadiorites above snow line are weathering to ferruginous bauxite. Calculations indicate that vermiculite is presently forming from phlogopite schists in this environment at a unit area rate that is approximately six times the average estimated rate of clay erosion for North America. The mineralogical data indicate that chemical weathering in this region is a quantitatively significant process, and suggest that in the development of current geomorphic concepts researchers may have generally underestimated the importance of chemical weathering in alpine environments.

Résumé

Résumé

De la vermiculite, un interstratifié vermiculite-phlogopite, et une smectite, se forment actuellement à partir de roches mère ignées et métamorphiques, dans la zone alpine des Northern Cascades, Washington. En plus, des quartz-diorites et des métadiorites situées au-dessus de la limite des neiges sur les versants face au Sud s’altèrent en bauxites ferrugineuses. Les calculs indiquent que la vermiculite est actuellement en formation à partir des schistes phlogopitiques de ce milieu, à une vitesse, par unité de surface, qui est approximativement six fois la vitesse moyenne estimée pour l’érosion de l’argile dans l’Amérique du Nord. Les données minéralogiques indiquent que l’altération chimique est, dans cette région, un processus quantitativement significatif, et suggèrent que dans le développement des concepts géomorphologiques courants, les chercheurs peuvent avoir généralement sous-estimé l’importance de l’altération chimique dans les milieux alpins.

Kurzreferat

Kurzreferat

Vermiculit, gemischt schichtiger Vermiculit-Phlogopit und Smectit werden gegenwärtig aus eruptivem und metamorphem Grundgestein in der alpinen Zone der nördlichen Cascades, Washington, gebildet. Darüber hinaus verwittern gegen den Süden weisende Quarz-Dioriten und Metadioriten oberhalb der Schneegrenze zu eisenschüssigem Bauxit. Berechnungen ergeben, dass sich Vermiculit gegenwärtig aus Phlogopitschiefern in diesem Milieur mit Einheitsflächengeschwindigkeit bildet, das ist etwa sechsmal der durchschnittlichen Schätzgeschwindigkeit der Tonerosion in Nordamerika. Die mineralogischen Messwerte deuten darauf hin, dass chemische Verwitterung in dieser Gegend ein quantitativ bedeutsamer Vorgang ist, und geben zu der Vermutung Anlass, dass bei der Entwicklung laufender geomorphischer Begriffe die Forschung möglicherweise die Bedeutung der chemischen Verwitterung in der alpinen Umgebung unterschätzt hat.

Резюме

Резюме

В альпийской зоне северной части Каскадов (шт. Вашингтон) происходит современное образование вермикулита, смешаннослойного вермикулит-флогопита и смектита по изверженным и метаморфическим породам. Кроме того обращенные к югу обнажения кварцевых диоритов и метадиоритов выше снеговой линии выветриваются с образованием железистого боксита. Проведенные вычисления показывают, что вермикулит в настоящее время образуется из флогопитовых сланцев со скоростью на единицу поверхности, которая примерно в 6 раз превышает среднюю скорость эрозии Северной Америки. Минералогические данные указывают, что химическое выветривание в этом регионе вызывает преобразование значительного количества материала и дает возможность предположить, что при развитии современных геоморфологических концепций исследователи, возможно, обычно недооценивают роль химического выветривания в условиях альпийского рельефа.

Type
Research Article
Copyright
Copyright © 1971, The Clay Minerals Society

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