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Cambro-Ordovician paleogeography of the southeastern New England Avalon Zone; implications for Gondwana breakup

M. D. Thompson, A. M. Grunow and J. Ramezani
Cambro-Ordovician paleogeography of the southeastern New England Avalon Zone; implications for Gondwana breakup
Geological Society of America Bulletin (January 2010) 122 (1-2): 76-88

Abstract

Paleomagnetic measurements and U-Pb geochronology of alkalic igneous rocks intruding the Ediacaran Cambridge Argillite and the Lower Cambrian Weymouth Formation north of Boston at Nahant, Massachusetts yield a well-constrained paleopole. The oldest intrusive phases are a syenodiorite sill and a granite dike with (super 206) Pb/ (super 238) U crystallization ages of 490.19+ or -0.90 Ma and 489.03+ or -0.82 Ma, respectively. This sequence along with undated mafic sills penetrating both the argillite and Weymouth strata are cut by 488.53+ or -0.81 Ma gabbro locally associated with 488.48+ or -0.79 Ma syenite forming a steep-sided intrusive plug. Ten paleomagnetic sampling sites within the mafic sills and the gabbro contain a stable A magnetic component with a mean direction of D=278.5 degrees , I=-76.7 degrees (A (sub 95) =3.9 degrees , N=10). This is considered to be the primary magnetization direction because it passes both fold and reversals tests. The corresponding paleopole at 320 degrees E, 34 degrees N (A (sub 95) =7.2 degrees , N=10) places the Southeastern New England Avalon Zone at a southerly paleolatitude of 65 degrees slightly removed from the African margin of Gondwana and suggests that bimodal Nahant magmatism is linked with latest Cambrian-Early Ordovician rifting of West Avalonia to form the Rheic Ocean. Stable B and C magnetic components in Nahant syenodiorite and syenite give rise to virtual geomagnetic poles that track Late Silurian through Carboniferous segments of the North American apparent polar wander path, indicating docking of West Avalonia by mid-Paleozoic time.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 122
Serial Issue: 1-2
Title: Cambro-Ordovician paleogeography of the southeastern New England Avalon Zone; implications for Gondwana breakup
Affiliation: Wellesley College, Department of Geosciences, Wellesley, MA, United States
Pages: 76-88
Published: 201001
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 86
Accession Number: 2010-015575
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2009186
Illustration Description: illus. incl. 2 tables, geol. sketch map
N42°19'60" - N42°25'00", W70°49'60" - E00°00'00"
Secondary Affiliation: Ohio State University, USA, United StatesMassachusetts Institute of Technology, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201010
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