Thermobarometric and fluid expulsion history of subduction zones
- 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), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B6; ISSN 0148-0227; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
Similar Records
The P-T-t history of blocks in serpentinite-matrix melange, west-central Baja California
The stability of subducted glaucophane with the Earth’s secular cooling
Related Subjects
580000* -- Geosciences
ALKANES
ALPS
CALIFORNIA
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
DEVELOPED COUNTRIES
DEVOLATILIZATION
ENVIRONMENTAL TRANSPORT
FEDERAL REGION IX
FLUIDS
GASES
GEOLOGIC HISTORY
HEAT FLOW
HYDROCARBONS
HYDROLOGY
INCLUSIONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MASS TRANSFER
MATERIALS
METAMORPHIC ROCKS
METAMORPHISM
METHANE
MINERALS
MOUNTAINS
NORTH AMERICA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PARAGENESIS
PERMEABILITY
PLATE TECTONICS
REMOVAL
RESERVOIR FLUIDS
RESERVOIR TEMPERATURE
ROCKS
SANDSTONES
SCHISTS
SEDIMENTARY ROCKS
SHALES
SILICATE MINERALS
SILTSTONES
SUBDUCTION ZONES
TECTONICS
USA
VAPORS
WATER REMOVAL
WATER VAPOR
ZEOLITES