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Shallow‐level metamorphic fluids in a high uplift rat metamorphic belt; Alpine Schist, New Zealand
Author(s) -
CRAW D.
Publication year - 1988
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1988.tb00405.x
Subject(s) - geology , metamorphic rock , schist , biotite , quartz , fluid inclusions , geochemistry , calcite , metamorphism , recrystallization (geology) , metamorphic facies , chlorite , mineralogy , petrology , facies , geomorphology , paleontology , structural basin
Fluids, some of which are CO 2 ‐rich (up to 40 mol.% CO 2 ) and some of which are highly saline (up to 18 wt% NaCl equivalent), are trapped as fluid inclusions in quartz‐calcite (∼ metallic minerals) veins which cross‐cut the pumpellyite‐actinolite to amphibolite facies rocks of the Alpine Schist. Fluids were commonly trapped as immiscible liquid‐vapour mixes in quartz and calcite showing open‐space growth textures. Fluid entrapment occurred at fluid pressures near 500 bars (possibly as low as 150 bars) at temperatures ranging from 260 to 330° C. Saline fluids may have formed by partitioning of dissolved salts into an aqueous phase on segregation of immiscible fluids from a low‐density CO 2 ‐rich fluid. Calcite deposited by these fluids has δ 13 C ranging from – 8.4 to – 11.5 and δ 18 O from + 4 to + 13. Isotopic data, fluid compositions and mode of occurrence suggest that the fluids are derived from high‐grade metamorphic rocks. Fluid interaction with wall‐rock has caused biotite crystallization and/or recrystallization in some rocks and retrogression of biotite to chlorite in other rocks. Fluid penetration through the rock is almost pervasive in many areas where permeability, probably related to Alpine Fault activity, has focussed fluids on a regional scale into fractured rocks. The fluid flow process is made possible by high uplift‐rates (in excess of 10 mm/year) bringing hot rocks near to the surface.