Sediment-derived fluids in subduction zones: Isotopic evidence from veins in blueschist and eclogite of the Franciscan Complex, California

Journal Article · Tue Oct 01 00:00:00 EDT 1991 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1991)019<1033:SDFISZ>2.3.CO;2· OSTI ID:5877768

Nelson, B K ^[1]

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1. Univ. of Washington, Seattle (United States)

Isotopic analyses of minerals from veins that cut high-grade blueschist and eclogite blocks in the central belt of the Franciscan Complex provide constraints on the chronology of metamorphic events and on the origin and movement of fluids within the subduction zone. A Rb-Sr age of 153 {plus minus}1 Ma obtained for minerals from veins and open cavities that formed contemporaneously with retrograde blueschist facies metamorphism is a minimum age for the prograde metamorphism. The veining precedes the last episode of sedimentary-matrix melange formation by a minimum 15 to 20 Ma, during which time the blocks must have been stored within the subduction complex at low temperatures and without undergoing penetrative deformation. Initial Nd-isotope compositions ({epsilon}{sub Nd}) of the vein minerals range from +10.8 to {minus}2.4, indicating that some fluids were derived predominantly from dehydration of subducted mid-ocean ridge basalt, but that other fluids had a component derived from subducted sediment. The provenance of the subducted sediment was within old continental crust, thus associating the Franciscan paleo-subduction complex with a continental craton by the time of vein formation.

• OSTI ID: 5877768
• Journal Information: Geology; (United States), Vol. 19:10; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
GEOLOGIC FORMATIONS
AGE ESTIMATION
METAMORPHISM
RESERVOIR FLUIDS
ENVIRONMENTAL TRANSPORT
SUBDUCTION ZONES
BASALT
DEFORMATION
DEHYDRATION
GEOCHEMISTRY
ISOTOPE RATIO
MINERALS
NEODYMIUM ISOTOPES
ORIGIN
RESERVOIR TEMPERATURE
RUBIDIUM ISOTOPES
SCHISTS
SEDIMENTS
STRONTIUM ISOTOPES
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
CHEMISTRY
DEVELOPED COUNTRIES
FLUIDS
IGNEOUS ROCKS
ISOTOPES
MASS TRANSFER
METAMORPHIC ROCKS
NORTH AMERICA
ROCKS
USA
VOLCANIC ROCKS
580000* - Geosciences