Progressive metamorphism of the Taitao Ophiolite; evidence for axial and off-axis hydrothermal alterations

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doi: 10.1016/j.lithos.2007.04.003
Author(s): Shibuya, Takazo; Komiya, Tsuyoshi; Anma, Ryo; Ota, Tsutomu; Omori, Soichi; Kon, Yoshiaki; Yamamoto, Shinji; Maruyama, Shigenori
Author Affiliation(s): Primary:
Tokyo Institute of Technology, Department of Earth and Planetary Science, Tokyo, Japan
University of Tsukuba, Japan
Okayama University at Misasa, Japan
Volume Title: Lithos (Oslo)
Source: Lithos (Oslo), 98(1-4), p.233-260. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0024-4937 CODEN: LITHAN
Note: In English. 83 refs.; illus., incl. 1 plate, 6 tables, geol. sketch maps
Summary: We estimated metamorphic conditions for the ∼6 Ma Taitao ophiolite, associated with the Chile triple junction. The metamorphic grade of the ophiolite, estimated from secondary matrix minerals, changes stratigraphically downwards from the zeolite facies, through the prehnite-actinolite facies, greenschist facies and the greenschist-amphibolite transition, to the amphibolite facies. The metamorphic facies series corresponds to the low-pressure type. The metamorphic zone boundaries are subparallel to the internal lithological boundaries of the ophiolite, indicating that the metamorphism was due to axial hydrothermal alteration at a mid-ocean ridge. Mineral assemblages and the compositions of veins systematically change from quartz-dominated, through epidote-dominated, to prehnite-dominated with increasing depth. Temperatures estimated from the vein assemblages range from ∼230°C in the volcanic unit to ∼380°C at the bottom of the gabbro unit, systematically ∼200°C lower than estimates from the adjoining matrix minerals. The late development of veins and the systematically lower temperatures suggest that the vein-forming alteration was due to off-axis hydrothermal alteration. Comparison between the Taitao ophiolite with its mid-ocean ridge (MOR) affinity, and other ophiolites and MOR crusts, suggests that the Taitao ophiolite has many hydrothermal alteration features similar to those of MOR crusts. This is consistent with the tectonic history that the Taitao ophiolite was formed at the South Chile ridge system near the South American continent (Anma, R., Armstrong, R., Danhara, T., Orihashi, Y. and Iwano, H., 2006. Zircon sensitive high mass-resolution ion microprobe U-Pb and fission-track ages for gabbros and sheeted dykes of the Taitao ophiolite, Southern Chile, and their tectonic implications. The Island Arc, 15(1): 130-142). Abstract Copyright (2007) Elsevier, B.V.
Year of Publication: 2007
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; 16 Structural Geology; Aisen del General Carlos Ibanez del Campo Chile; Alkaline earth metals; Amphibolites; Bahia Barrientos; Chain silicates; Chemical composition; Chile; Chlorite; Chlorite group; Crystal zoning; DSDP Site 504; East Pacific; Epidote; Epidote group; Equatorial Pacific; Feldspar group; Framework silicates; Guatemala Basin; Hess Deep; Hydrothermal alteration; Magnesium; Metals; Metamorphic rocks; Metamorphism; Metasomatism; Mineral composition; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Ophiolite; Ophiolite complexes; Orthosilicates; Pacific Ocean; Panama Basin; Petrology; Plagioclase; Prehnite; Pyroxene group; Secondary minerals; Sheet silicates; Silicates; Sorosilicates; South America; Southern Chile; Taitao Ophiolite; Taitao Peninsula; Veins; Zeolite group
Coordinates: S433000 S433000 W0753000 W0753000
N064400 N064400 W0915600 W0915600
Record ID: 2008044623
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands