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Garnet-chloritoid-paragonite metapelite from the Chuacus Complex (central Guatemala); new evidence for continental subduction in the North America-Caribbean plate boundary

Roberto Maldonado, Fernando Ortega-Gutierrez and David Hernandez-Uribe
Garnet-chloritoid-paragonite metapelite from the Chuacus Complex (central Guatemala); new evidence for continental subduction in the North America-Caribbean plate boundary
European Journal of Mineralogy (October 2016) 28 (6): 1169-1186

Abstract

We describe for the first time the presence of high-pressure metapelites in the northern Chuacus Complex of Central Guatemala. Garnet-chloritoid-paragonite-bearing pelitic schist occurs in a predominantly metasedimentary sequence consisting of intercalated garnet paragneisses, pelitic schists, impure marbles, granitic orthogneisses and minor garnet amphibolites, an association that denotes a passive continental margin origin. The metapelite we have studied is mainly composed of almandine-rich garnet porphyroblasts in a schistose matrix consisting of phengite, paragonite, quartz, chloritoid and rutile, with minor amounts of chlorite, epidote, Fe-Ti oxides and sporadic kyanite. The metapelite also includes fine-grained paragonite + quartz and paragonite + epidote aggregates, which resemble jadeite and lawsonite pseudomorphs, respectively. A late staurolite-bearing assemblage overprints the high-pressure paragenesis. We have used a phase-equilibria modeling approach to constrain the P-T conditions of metamorphism. Equilibrium phase diagrams were calculated in the system MnNCKFMASHTO (MnO-Na (sub 2) O-CaO-K (sub 2) O-FeO-MgO-Al (sub 2) O (sub 3) -SiO (sub 2-) -H (sub 2) O-TiO (sub 2) -Fe (sub 2) O (sub 3) ) for three hypothetical effective bulk-compositions. The compositions of garnet, chloritoid and phengite cores indicate they crystallized during an early stage of prograde high-pressure metamorphism at 20-21 kbar and 500-540 degrees C. The composition of garnet rims constrains the P-T peak conditions to approximately 19.5-20 kbar and 580-600 degrees C. Both the zoning pattern of the garnet and the calculated P-T path indicate that the studied metapelite could be formed during a single progressive metamorphic event along a subduction geothermal gradient of 7-9 degrees C/km. The retrograde path is less well constrained, although decreasing pressure coupled with a slight drop of temperature are indicated by the absence of biotite and the growth of post-peak chlorite and epidote. Moreover, a late-stage heating event is required, in order for the metapelite to reach the stability field of staurolite at 7-8 kbar and 590-620 degrees C. The occurrence of this high-pressure metapelite implies that high-pressure metamorphism in the Chuacus Complex must have extended at least 10 km further to the north than previously thought. We propose that both Chuacus Complex and Rabinal Granite show a succession of decreasing P-T peak conditions towards the north, which may preserve in part the original thermal structure of the subduction zone in the southern margin of North America during the Cretaceous.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 28
Serial Issue: 6
Title: Garnet-chloritoid-paragonite metapelite from the Chuacus Complex (central Guatemala); new evidence for continental subduction in the North America-Caribbean plate boundary
Affiliation: Universidad Nacional Autonoma de Mexico, Instituto de Geologia, Mexico City, Mexico
Pages: 1169-1186
Published: 20161017
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 69
Accession Number: 2016-094587
Categories: Igneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N15°04'00" - N15°04'00", W90°28'60" - W90°28'60"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201646
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