extrusive rock


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Related to extrusive rock: Intrusive Rock

extrusive rock

[ik′strü·siv ′räk]
(geology)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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In addition, it is found that extrusive rocks (e.g., basalt and dacite) have much higher [kappa] compared to plutonic rocks; hypabyssal and pyroclastic rocks have relatively lower [kappa] (Table 2).
The extrusive rocks of the Sambava-Vohemar area are products of volcanic activity related to the Marion Hotspot, which, it is believed, was very active in the Upper Cretaceous (Meert and Tamrat, 2006; Torsvik et al., 1998).
It is worth mentioning that, according to the geophysical data, extrusive rocks forming the Deecan Plateau of India (famous for zeolites and associated minerals) are related to another hotspot active in the same region (but genetically younger at ~67 million years)--the Reunion Hotspot.
Resting unconformably on these units are volcanic rocks of the Elenita (Triassic-Jurassic) and Henrietta (Jurassic) Formations, both intruded by plutons of Jurassic age--the extrusive rocks are the remnants of a volcanic arc which once extended from California into the Mexican state of Durango.
The oldest extrusive rocks are capped by a Quaternary basalt flow several hundred feet thick.