Skip to Main Content
Book Chapter

Petrologic characterization of Guatemalan lawsonite eclogite: Eclogitization of subducted oceanic crust in a cold subduction zone

By
Tatsuki Tsujimori
Tatsuki Tsujimori
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA
Search for other works by this author on:
Virginia B. Sisson
Virginia B. Sisson
Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024-5192, USA
Search for other works by this author on:
Juhn G. Liou
Juhn G. Liou
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA
Search for other works by this author on:
George E. Harlow
George E. Harlow
Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024-5192, USA
Search for other works by this author on:
Sorena S. Sorensen
Sorena S. Sorensen
Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560-0119, USA
Search for other works by this author on:
Published:
January 01, 2006

Early Cretaceous lawsonite eclogites and related high-pressure rocks occur as tectonic inclusions within serpentinite mélange 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 S1–S2 foliation. The prograde assemblage is garnet (X Mg = ∼0.22) + omphacite (∼52 mol% jadeite) or jadeite (∼83 mol % jadeite) + lawsonite + chlorite + rutile + quartz ± 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, Fe2+-Mg distribution coefficients between omphacite inclusions and adjacent garnet with Ln(K D) = 2.7–4.5, and garnet-clinopyroxene-phengite thermobarometry suggest that eclogitization initiated at temperature (T) = ∼300 °C and pressure (P) > 1.1 GPa, and continued to T = ∼480 °C and P = ∼2.6 GPa. In contrast, the retrograde eclogite-facies assemblage is characterized by reversely zoned garnet rims and omphacite ± glaucophane + lawsonite + rutile + quartz ± phengite (3.5 Si p.f.u.) along the S3 foliation. Garnet-phengite-clinopyroxene thermobarometry yields P = ∼1.8 GPa and T = ∼400 °C. The youngest, blueschist-facies assemblage (glauco-phane + lawsonite + chlorite + titanite + quartz ± phengite) locally replaces earlier mineral assemblages along S4 crenulations. The inferred prograde P-T trajectory lies near a geotherm of ∼5 °C km−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 = ∼300 °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 ∼100 km in cold subduction zones, dehydration embrittlement may be caused by such chlorite-consuming reactions.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

Ultrahigh-pressure metamorphism: Deep continental subduction

Bradley R. Hacker
Bradley R. Hacker
Search for other works by this author on:
William C. McClelland
William C. McClelland
Search for other works by this author on:
J.G. Liou
J.G. Liou
Search for other works by this author on:
Geological Society of America
Volume
403
ISBN print:
9780813724034
Publication date:
January 01, 2006

References

Related

Citing Books via

Related Articles
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal