Formation of interlayered blueschist and greenschist in the Coastal Cordillera (Central Chile): Effects of protolith heterogeneity, fluid infiltration or thermal overprinting?.

Halama, Ralf, Brandt, Sönke and Garbe-Schönberg, Dieter (2010) Formation of interlayered blueschist and greenschist in the Coastal Cordillera (Central Chile): Effects of protolith heterogeneity, fluid infiltration or thermal overprinting?. [Talk] In: SFB 574 Subduction Workshop. , 04.-07.11.2010, Pucon, Chile .

Full text not available from this repository. (Contact)

Abstract

The interlayering of metamorphic rocks that represent distinct metamorphic facies has been attributed to three causes: 1. Differences in the P-T conditions of equilibration, 2. Chemical differences of the layers inherited from the protolith, and 3. Differences in the degree of retrograde fluid infiltration.
Investigations of such interlayered sequences can shed light on the mobility of trace elements, chemical equilibration and fluid-rock interaction during metamorphism.
In the Coastal Cordillera of Central Chile, a spectacular sequence of interlayered blueschists and greenschists occurs in coastal outcrops near Pichilemu. To identify the processes responsible for interlayering and to constrain the P-T evolution, geochemical analyses were combined with petrologic investigations.
The layering on a cm-to-dm scale suggests that all rocks have experienced a similar P-T evolution. For adjacent blueschist-greenschist pairs, blueschists have consistently higher SiO2 and Na2O contents, whereas greenschists are
relatively enriched in Al, Mg and total Fe. Pseudosection calculations using the THERIAK-DOMINO software indicate that stability of glaucophane is extended towards higher T and lower P for typical blueschist compared to greenschist compositions. Hence, layering is the result of chemical
differences.
Geochemical trends inconsistent with magmatic differentiation and similar concentrations of incompatible trace elements between blueschist-greenschist pairs demonstrate that primary igneous processes cannot have caused the chemical heterogeneities. Instead, mobilization of fluid-mobile elements (Cs, Rb, Ba, K) and relationships between these elements that are consistent with a metasomatic overprint suggest fluid-induced transport. This metasomatic process highlights the role of fluids during subduction and their influence on phase stability and element mobility

Document Type: Conference or Workshop Item (Talk)
Keywords: subduction
Research affiliation: OceanRep > SFB 574 > C1
OceanRep > SFB 574
Kiel University
Date Deposited: 10 Dec 2010 12:17
Last Modified: 27 Jan 2012 05:01
URI: http://oceanrep.geomar.de/id/eprint/10417

Actions (login required)

View Item View Item