Factors Controlling the Distribution of Zeolites in the Andesitic Rocks of the Central Coastal Range of Eastern Taiwan

Abstract

This study is a survey of zeolites in the andesitic rocks of the Central Coastal Range (CCR) of eastern Taiwan. Methods of the study include field observations and laboratory techniques such as X-ray diffraction, petrography, and scanning electron microscopy.

It is found that zeolites are abundant only in the andesitic rocks along two streamlets, i.e., Tuwi-His (TH) and Yungshui-His (YH), and are rare to absent in others. Zeolites generally occur in hyaloclastites but rarely in lava flows in the TH section. On the other hand, breccias are usually richer in zeolites than lava flows, peperites, and tuffs in the YH section. Natrolite is the unique zeolite in TH hyaloclastites. It usually associates with apophyllite and calcite. Ph illipsite is the only zeolite in YH breccias. It mostly occurs alone and occasionally associates with calcite.

The duration of exposure to seawater is considered as the main factor influencing the amount of zeolites in submarine erupted andesitic rocks of the CCR. The longer the andesitic rocks are exposed to seawater, the larger the amount of zeolites would be in them. On the other hand, the species of zeolite and related authigenic minerals in the andesitic rocks of the CCR are presumably controlled by the kind of their phenocrysts which are the essential minerals suffered from alteration.

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