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Massive sulfide metallogenesis at a late Mesozoic sediment-covered spreading axis: Evidence from the Franciscan complex and contemporary analogues

Geology

By:
, , , and
https://doi.org/10.1130/0091-7613(1993)021<0137:MSMAAL>2.3.CO;2

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Abstract

The Island Mountain deposit, an anomalous massive sulfide in the Central belt of the Franciscan subduction complex, northern California Coast Ranges, formed during hydrothermal activity in a sediment-dominated paleo-sea-floor environment. Although the base of the massive sulfide is juxtaposed against a 500-m-wide melange band, its gradational upper contact within a coherent sequence of sandstone, siltstone, and mudstone indicates that hydrothermal activity was concurrent with turbidite deposition. Accumulations of sulfide breccia and clastic sulfide were produced by mass wasting of the sulfide mound prior to burial by turbidites. The bulk composition of sulfide samples (pyrrhotite rich; high Cu, As, and Au contents; radiogenic Pb isotope ratios) is consistent with a hydrothermal system dominated by fluid-sediment interaction. On the basis of a comparison with possible contemporary tectonic analogues at the southern Gorda Ridge and the Chile margin triple junction, we propose that massive sulfide mineralization in the Central belt of the Franciscan complex resulted from hydrothermal activity at a late Mesozoic sediment-covered ridge axis prior to collision with the North American plate.

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Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Massive sulfide metallogenesis at a late Mesozoic sediment-covered spreading axis: Evidence from the Franciscan complex and contemporary analogues
Series title:
Geology
DOI:
10.1130/0091-7613(1993)021<0137:MSMAAL>2.3.CO;2
Volume:
21
Issue:
2
Year Published:
1993
Language:
English
Publisher:
GSA Publications
Contributing office(s):
Alaska Science Center
Description:
4 p.
First page:
137
Last page:
140
Country:
United States
State:
California