초록

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Abstract ▼ AI-Helper

The Dongmakgol Tuff, dated to be 103.1 ± 3.2 Ma by Rb-Sr method, consists of voluminous ignimbrites with intercalations of thin bedded tuffs in two horizons. It illustrates many features of a compound cooling unit with nonwelding or partial welding zones along the horizons. Noticeable exposures al...

The Dongmakgol Tuff, dated to be 103.1 ± 3.2 Ma by Rb-Sr method, consists of voluminous ignimbrites with intercalations of thin bedded tuffs in two horizons. It illustrates many features of a compound cooling unit with nonwelding or partial welding zones along the horizons. Noticeable exposures along the valleys and cliffs exhibit vertical and horizontal changes in degree of welding and crystallization, from which the ignimbrites can be divided into several welding and crystallization zones. The welding zones in two ignimbrites are generally divided into outer nonwelding zones, middle partial welding zones and inner dense welding zones, and rheomorphic zones between the partial and dense welding zones. Thick devitrified zones commonly overprint much portion of the dense and partial welding zones, whereas thin vapor-phase crystallization zones locally develop in the contact of the partial welding zones with dense welding zones. Welding in the Dongmakgol Tuff initiated during and after emplacement of pyroclastic flows. Early crystallization followed welding to devitrify the vitric tuffs and later vapor-phase crystallization locally occurred to overprint the devitrified zones.

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