Preservation of primary volcanic textures in the ultrahigh-pressure terrain of Dabie Shan

Delicate primary volcanic features such as ash layers, volcaniclastic breccias, and pillow lavas with amygdaloidal rims have been identified in a terrigenous volcanosedimentary sequence forming part of the ultrahigh-pressure unit of the Dabie Shan, China. The presence of coesite relics in crosscutti...

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Bibliographic Details
Published in:Geology (Boulder) 2002-08, Vol.30 (8), p.699-702
Main Authors: Oberhänsli, R, Martinotti, G, Schmid, R, Liu, X
Format: Article
Language:English
Subjects:
Anhui China
Asia
China
Dabie Mountains
dikes
Far East
Ganghe Valley
Geology
Hubei China
igneous and metamorphic rocks
intrusions
Lava
metamorphic rocks
metamorphism
metavolcanic rocks
P-T conditions
Petrology
pillow lava
pressure
reaction rims
terrigenous materials
textures
ultrahigh pressure
ultrametamorphism
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Summary:Delicate primary volcanic features such as ash layers, volcaniclastic breccias, and pillow lavas with amygdaloidal rims have been identified in a terrigenous volcanosedimentary sequence forming part of the ultrahigh-pressure unit of the Dabie Shan, China. The presence of coesite relics in crosscutting dikes confirms an ultrahigh-pressure evolution for the entire sequence. Evaluation of the probable reaction history for zeolite compositions as supposed for the amygdaloidal rims reveals a scarcity of reactions at very high pressures. Such special conditions of low reactivity and fluid-conserving reactions, combined with a lack of directed stress, have allowed the remarkable preservation of these primary volcanic features despite deep subduction.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(2002)030<0699:POPVTI>2.0.CO;2