Cracking at the magma-hydrothermal transition; evidence from the Troodos Ophiolite, Cyprus

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doi: 10.1016/S0012-821X(99)00087-4
Authors:Gillis, K. M.; Roberts, M. D.
Author Affiliations:Primary:
University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada
Other:
James Cook University, Australia
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 169(3-4), p.227-244. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1999
Note:In English. 59 refs.; illus., incl. 3 tables, geol. sketch map
Summary:The nature of the magma-hydrothermal transition in oceanic hydrothermal systems is poorly understood, in part because the geological relations in this critical region have rarely been observed in modern ocean crust. Detailed mapping was conducted in the Troodos Ophiolite, Cyprus, where a gabbronorite sequence intrudes the sheeted dyke complex, which is truncated at its base by a thin contact aureole composed of massive hornfels. Geothermometric data for hornblende and pyroxene hornfels show that hydrated sheeted dykes were recrystallized at amphibolite to granulite facies conditions (778-986°C). Quartz diorite veins and apophyses, and monomineralic amphibole veins cross-cut the contact aureole and show no preferred age relationships. Geothermometric data indicate that quartz diorite was injected at 817-919°C and that fractures were filled with amphibole at 575-750°C. Phase relations of quartz-hosted, halite-bearing fluid inclusions in quartz diorite veins constrain minimum entrapment temperatures of 225-520°C (average 402°C) and minimum pressures that span lithostatic and hydrostatic conditions. We believe that these characteristics are indicative of a conductive boundary layer that separates an active hydrothermal system from the heat source that drives it. Field and petrological data indicate that transient fracturing caused oscillations in temperature and pressure conditions within the conductive boundary layer, and mixing of hydrothermal and magmatic fluids at the magma-hydrothermal interface. Cross-cutting relations between magmatic and hydrothermal vein networks show that fracturing occurred prior to the cessation of magmatic activity. We explore plausible models for the causes and consequences of fracturing that consider the role of dyke injection, thermoelastic stresses, and volatile build-up. Abstract Copyright (1999) Elsevier, B.V.
Sections:Petrology
Subsections:Oceanic petrology
Subjects:Amphibolite facies; Aureoles; Boundary conditions; Contact metamorphism; Crust; Dikes; Emplacement; Facies; Fluid inclusions; Fracturing; Gabbros; Geologic barometry; Geologic thermometry; Granulite facies; Hornfels; Hydrothermal conditions; Igneous rocks; Inclusions; Intrusions; Magmas; Metamorphic rocks; Metamorphism; Microthermometry; Mineral assemblages; Norite; Oceanic crust; Ophiolite complexes; P-T conditions; Plutonic rocks; Plutons; Recrystallization; Sheeted dikes; Troodos Ophiolite; Veins; Windows; Asia; Cyprus; Middle East; Platanistasa Window
Coordinates:N350000 N350000 E0330000 E0330000
Abstract Numbers:00M/1018
Record ID:1999043442
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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