Thermobarometric and fluid expulsion history of subduction zones

Journal Article · Sun Jun 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB06p09047· OSTI ID:5073556

Ernst, W G ^[1]

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1. Univ. of California, Los Angeles (United States)

Phanerozoic, unmetamorphosed, weathered, and altered lithotectonic complexes subjected to subduction exhibit the prograde metamorphic facies sequence: zeolite {r arrow} prehnite-pumpellyite {r arrow} glaucophane schist {r arrow} eclogite. Parageneses reflect relatively high-P trajectories, accompanied by semicontinuous devolatilization. The thermal evolution of convergent plate junctions results in early production of high-rank blueschists, high-P amphibolites, and eclogites at depth. Inclusion studies suggest that two-phase immiscible volatiles are evolved in turn during progressive metamorphism of the subducted sections. Expulsion of pore fluids and transitions from weathered and altered supracrustal rocks to zeolite facies assemblages release far more fluid than the better understood higher-grade transformations. Many blueschist parageneses (e.g., Western Alps) have been partially overprinted by later greenschist and/or epidote-amphibolite facies assemblages. Less common blueschist terranes (e.g., Franciscan belt of western California) preserve metamorphic aragonite and other high-P minerals, and lack a low-pressure overprint; physical conditions during retrogression approximately retraced the prograde path or, for early formed high-grade blocks, reflect somewhat higher pressures and lower temperatures. The ease with which volatiles are expelled from a subduction complex and migrate upward along the plate junction zone is roughly proportional to the sandstone/shale ratio: low-permeability mudstones tend to maintain P{sub fluid} values approaching lithostatic, lose strength, and deform chaotically (forming melange belts), whereas permeable sandstone-rich sections retain structural/stratigraphic coherence and fail brittlely (forming coherent terranes).

• OSTI ID: 5073556
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B6; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
RESERVOIR FLUIDS
ENVIRONMENTAL TRANSPORT
SUBDUCTION ZONES
HYDROLOGY
ALPS
CALIFORNIA
CARBON DIOXIDE
DEVOLATILIZATION
GEOLOGIC HISTORY
HEAT FLOW
INCLUSIONS
METAMORPHISM
METHANE
PARAGENESIS
PERMEABILITY
PLATE TECTONICS
RESERVOIR TEMPERATURE
SANDSTONES
SCHISTS
SHALES
SILTSTONES
WATER REMOVAL
WATER VAPOR
ZEOLITES
ALKANES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
DEVELOPED COUNTRIES
FEDERAL REGION IX
FLUIDS
GASES
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MASS TRANSFER
MATERIALS
METAMORPHIC ROCKS
MINERALS
MOUNTAINS
NORTH AMERICA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
REMOVAL
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
TECTONICS
USA
VAPORS
580000* - Geosciences