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Evidence for a ridge subduction event in the Ordovician rocks of north-central Maine

Adam Schoonmaker and William S. F. Kidd
Evidence for a ridge subduction event in the Ordovician rocks of north-central Maine
Geological Society of America Bulletin (August 2006) 118 (7-8): 897-912

Abstract

Modern and past ridge subduction events are characterized by the intrusion of mid-ocean-ridge basalt (MORB) magmas into an overlying accretionary prism. The field relationships and trace-element geochemistry of Ordovician mafic igneous rocks of the Weeksboro-Lunksoos and Munsungun anticlinoria of north-central Maine indicate that they resulted from such an event. The Bean Brook gabbro intrudes the Hurricane Mountain melange and other related sedimentary strata of continental derivation. The gabbro and associated Dry Way volcanics have MORB trace-element chemistries, while the Bluffer Pond and Stacyville volcanics are more enriched (EMORB), all of which indicate derivation from a mid-ocean ridge. On petrogenetic diagrams, mafic samples plot in MORB fields, or when Th is used as a discriminator, in arc fields along trends that originate from MORB fields and extend toward the composition of upper continental crust. These trends are consistent with the presence of silicic and metasedimentary xenoliths in the Dry Way volcanics and Bean Brook gabbro and indicate the magmas were not subduction products, but were contaminated by Thrich upper continental crust.The nearby Chain Lakes Massif likely represents the basement to the "Chain Lakes microcontinent," and the geographic relationship and ages of the massif, Hurricane Mountain melange, and Dry Way-Bean Brook magmatic rocks indicate northwest-directed subduction (modern coordinates) on the southeastern margin of the Chain Lakes microcontinent, within the Early to Middle Ordovician Taconic ocean. Subduction at this boundary probably terminated because of the ridge subduction, analogous to Neogene California.


ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 118
Serial Issue: 7-8
Title: Evidence for a ridge subduction event in the Ordovician rocks of north-central Maine
Affiliation: State University of New York at Albany, Department of Earth and Atmospheric Sciences, Albany, NY, United States
Pages: 897-912
Published: 200608
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 64
Accession Number: 2006-056743
Categories: Geochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2006144
Illustration Description: illus. incl. sect., 1 table, geol. sketch map
N45°52'00" - N45°52'60", W69°16'00" - W69°13'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200616
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