Phengite-Based Chronology of K- and Ba-Rich Fluid Flow in Two Paleosubduction Zones

Abstract

Subduction recycles aqueous fluids from slab and sediment to the mantle. Subduction zones are long-lived, but time scales for fluid-rock interaction within subduction complexes are uncertain. Large-ion lithophile elements (potassium and barium) were added to eclogite (subducted basalt) during high pressure/temperature metamorphism via phengite crystallization from subduction zone fluids. Phengite grains from eclogite blocks and their metasomatic selvages yielded 40Ar/39Ar ages across grains and between samples that indicate 25 and 60 million years of fluid-rock interaction in the Samana Complex, Dominican Republic, and the Franciscan Complex, California, respectively.

First 40Ar-39Ar Ages from Low-T Mafic Blueschist Blocks in a Franciscan Mélange near San Simeon: Implications for Initiation of Subduction

“…The nearly coeval metamorphic ages of the actinolite rind and host low-T blueschist block (04-EU-SS-45) obtained in this study are in agreement with results obtained for actinolitic rinds associated with other Franciscan high-T blueschist and eclogite blocks (e.g., Catlos and Sorensen 2003;figs. 1, 3).…”

“…McDowell et al (1984) presented numerous mineral and whole-rock K-Ar ages that were obtained as part of the regional mapping transect reported by Maxwell (1974). Recently, Ar-Ar ages were reported in important studies by Catlos and Sorensen (2003) and Wakabayashi and Dumitru (2007).…”

“…Map is after Jennings (1966), Cloos (1986), Shervais et al (2004), Ernst et al (2009), Wakabayashi andDumitru (2007), and Jacobson et al (2011). The following sources are referenced (see inset labeled "Sources"): Lee et al (1964), Suppe (1969), Firsov and Dobretsov (1970), Coleman and Lanphere (1971), Suppe and Armstrong (1972), Lanphere et al (1978), Mattinson andEcheverria (1980), McDowell et al (1984), Mattinson (1986), Ross and Sharp (1988), Grove and Bebout (1995), Catlos and Sorensen (2003), Grove et al (2003Grove et al ( , 2008, Anczkiewicz et al (2004), Wakabayashi and Dumitru (2007), and Mulcahy et al (2009). geochronological results for mafic blueschists from the Nacimiento Block (Ernst 1980;Page 1981), located to the west of the San Andreas Fault ( fig. 1).…”

“…Many radiometric ages have been obtained from the coarse-grained, high-T (450Њ-550ЊC) garnet-epidote blueschist and very rare eclogite blocks that are widely distributed but volumetrically minor components of the Central Belt mé lange ter- Manuscript received April 3, 2011;accepted March 30, 2012. * Author for correspondence; present address: Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, University Station, Box X, Austin,Texas 78713; rane (e.g., Coleman and Lanphere 1971;Moore 1984;Catlos and Sorensen 2003). Many ages have also been obtained from the mostly metasedimentary terranes forming the Eastern Belt (e.g., Suppe 1969;Suppe and Armstrong 1972;Lanphere et al 1978).…”

Paleostress evolution during the exhumation of high-P marbles, Samaná Complex, northern Hispaniola

“…Aunque la formación de zonas de cizalla retrógradas a menudo se nuclea en precursores frágiles con presencia de fluidos (i.e., Brander et al, 2012;Pittarello et al, 2012), en un estadio temprano de convergencia oceánica la caída drás-tica de la resistencia mecánica de los mármoles para producir cataclasis al comienzo de la exhumación requiere necesariamente una elevada presión de fluidos (Pf), de manera que el valor máximo de |s1-s3| en el que se produce la transición frágil-dúctil, se aproxime a la diferencia entre Pl-Pf. La presencia de fluidos fue también necesaria durante la eclogitización de las rocas del complejo de Samaná porque controló los procesos metasomáticos en el canal de subducción durante al menos 25 Ma (Catlos and Sorensen, 2003). Por lo tanto, resulta probable que al inicio de la exhumación del complejo de HP/LT de Samaná la Pf fuera también elevada.…”