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Petrologic characterization of Guatemalan lawsonite eclogite; eclogitization of subducted oceanic crust in a cold subduction zone

Tatsuki Tsujimori, Virginia B. Sisson, Juhn G. Liou, George E. Harlow and Sorena S. Sorensen
Petrologic characterization of Guatemalan lawsonite eclogite; eclogitization of subducted oceanic crust in a cold subduction zone (in Ultrahigh-pressure metamorphism; deep continental subduction, Bradley R. Hacker (editor), William C. McClelland (editor) and Juhn G. Liou (editor))
Special Paper - Geological Society of America (2006) 403: 147-168


Early Cretaceous lawsonite eclogites and related high-pressure rocks occur as tectonic inclusions within serpentinite melange south of the Motagua fault zone, Guatemala. Petrologic and microtextural analyses of mafic high-pressure rocks reveal three metamorphic stages linked to several deformational textures. The prograde stage represents an incipient eclogitization and is preserved in prograde garnet, along with an older S (sub 1) -S (sub 2) foliation. The prograde assemblage is garnet (X (sub Mg) = approximately 0.22) + omphacite ( approximately 52 mol % jadeite) or jadeite ( approximately 83 mol % jadeite) + lawsonite + chlorite + rutile + quartz+ or -phengite (3.6 Si p.f.u.); some rocks also have ilmenite and rare ferro-glaucophane. Lawsonite in garnet of some lawsonite eclogites contains rare pumpellyite inclusions. The presence of synmetamorphic brittle deformation, inclusions of pumpellyite, Fe (super 2+) -Mg distribution coefficients between omphacite inclusions and adjacent garnet with Ln(K (sub D) ) = 2.7-4.5, and garnet-clinopyroxene-phengite thermo-barometry suggest that eclogitization initiated at temperature (T) = approximately 300 degrees C and pressure (P) >1.1 GPa, and continued to T = approximately 480 degrees C and P = approximately 2.6 GPa. In contrast, the retrograde eclogite-facies assemblage is characterized by reversely zoned garnet rims and omphacite+ or -glaucophane + lawsonite + rutile + quartz+ or -phengite (3.5 Si p.f.u.) along the S (sub 3) foliation. Garnet-phengite-clinopyroxene thermobarometry yields P = approximately 1.8 GPa and T = approximately 400 degrees C. The youngest, blueschist-facies assemblage (glauco-phane + lawsonite + chlorite + titanite + quartz+ or -phengite) locally replaces earlier mineral assemblages along S (sub 4) crenulations. The inferred prograde P-T trajectory lies near a geotherm of approximately 5 degrees C km (super -1) , comparable to the calculated thermal and petrologic structure of the NE Japan subduction zone. These petrologic characteristics indicate: (1) the basalt-eclogite transformation may occur at T = approximately 300 degrees C in cold subduction zones, (2) glaucophane-bearing prograde assemblages are rare during incipient eclogitization in cold subduction zones, and (3) the chlorite-consuming reactions that form Fe-Mg-Mn garnet are more effective than the lawsonite-consuming reaction that forms a grossular component. At depths of approximately 100 km in cold subduction zones, dehydration embrittlement may be caused by such chlorite-consuming reactions.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Serial Volume: 403
Title: Petrologic characterization of Guatemalan lawsonite eclogite; eclogitization of subducted oceanic crust in a cold subduction zone
Title: Ultrahigh-pressure metamorphism; deep continental subduction
Author(s): Tsujimori, TatsukiSisson, Virginia B.Liou, Juhn G.Harlow, George E.Sorensen, Sorena S.
Author(s): Hacker, Bradley R.editor
Author(s): McClelland, William C.editor
Author(s): Liou, Juhn G.editor
Affiliation: Stanford University, Department of Geological and Environmental Sciences, Stanford, CA, United States
Affiliation: University of California Santa Barbara, Geological Sciences Institute for Crustal Studies, Santa Barbara, CA, United States
Pages: 147-168
Published: 2006
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 100
Accession Number: 2006-069361
Categories: Igneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N10°00'00" - N20°00'00", W90°00'00" - W60°00'00"
Secondary Affiliation: University of Idaho, USA, United StatesStanford University, USA, United StatesAmerican Museum of Natural History, USA, United StatesNational Museum of Natural History, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200640
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