Metasomatic alteration of an early Archean komatiite sequence into chert: field and petrographic evidence

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6651060

Duchac, K C; Hanor, J S

Stratiform units of pervasively silicified ultramafic rock occur near the top of the Onverwacht group, Barberton Mountian Land, South Africa. The origin of these units has been variously ascribed to early Archean subaerial weathering, submarine weathering, cataclastic metamorphism, and the alteration of silicic tuffs at the top of mafic to felsic volcanic sequences. The authors have studied a 40 m thick stratigraphic sequence that is exceptionally well-exposed for 1.5 km within the Skokohla River valley. Well-preserved ghosts of spinifex- and cumulate-olivines and pyroxenes establish the komatiitic ancestry of these rocks. The entire sequence has been pervasively altered, however, to cherts dominated by quartz and Cr-rich muscovite and containing lesser and variable amounts of chlorite, dolomite, rutile, and chrome spinel. The present Skokohla rocks can be divided into five distinct correlatable facies of laterally variable thickness which probably represent different flow units. Alteration apparently occurred early, prior to any significant tectonic deformation. The observed pervasive sericitization is inconsistent with an origin by subaerial weathering. It is most likely that the sequence was altered by large volumes of ascending hydrothermal fluids.

• Research Organization: Louisiana State Univ., Baton Rouge (USA)
• OSTI ID: 6651060
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
152003 -- Geothermal Data & Theory-- Rock-Water-Gas Interactions
58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
AFRICA
CHERT
FLUIDS
GEOLOGY
GEOTHERMAL FLUIDS
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
METAMORPHISM
MINERALOGY
PETROGENESIS
PETROGRAPHY
ROCK-FLUID INTERACTIONS
ROCKS
SEDIMENTARY ROCKS
SOUTH AFRICA
STRATIGRAPHY
TECTONICS
VOLCANIC ROCKS