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Titolo:
PALEOMAGNETISM, MAGNETIC-ANISOTROPY, AND MIDCRETACEOUS PALEOLATITUDE OF THE DUKE-ISLAND (ALASKA) ULTRAMAFIC COMPLEX
Autore:
BOGUE SW; GROMME S; HILLHOUSE JW;
Indirizzi:
OCCIDENTAL COLL,DEPT GEOL LOS ANGELES CA 90041 US GEOL SURVEY MENLO PK CA 94025
Titolo Testata:
Tectonics
fascicolo: 5, volume: 14, anno: 1995,
pagine: 1133 - 1152
SICI:
0278-7407(1995)14:5<1133:PMAMPO>2.0.ZU;2-A
Fonte:
ISI
Lingua:
ENG
Soggetto:
COAST PLUTONIC COMPLEX; CENTRAL BRITISH-COLUMBIA; REGIONAL TILT RATHER; CENTRAL SOUTHEASTERN ALASKA; LARGE-SCALE DISPLACEMENT; CANADIAN CORDILLERA; NORTH-AMERICA; TERRANE-I; ROCKS; MARGIN;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
67
Recensione:
Indirizzi per estratti:
Citazione:
S.W. Bogue et al., "PALEOMAGNETISM, MAGNETIC-ANISOTROPY, AND MIDCRETACEOUS PALEOLATITUDE OF THE DUKE-ISLAND (ALASKA) ULTRAMAFIC COMPLEX", Tectonics, 14(5), 1995, pp. 1133-1152

Abstract

We report paleomagnetic results from layered igneous rocks that implysubstantial post mid-Cretaceous poleward motion of the Insular superterrane (western Canadian Cordillera and southeast Alaska) relative to North America. The samples studied are from the stratiform zoned ultramafic body at Duke Island, which intruded rocks of the Alexander terrane at the south end of the southeastern Alaska archipelago at about 110 Ma. Thermal and alternating field demagnetization experiments show that the characteristic remanence of the ultramafic rocks has high coercivity and a narrow unblocking temperature range just below the Curie temperature of magnetite. This remanence is likely carried by low-Ti titanomagnetite exsolved within clinopyroxene and perhaps other silicate hosts. The Duke Island intrusion exhibits a well-developed gravitational layering that was deformed during initial cooling (but below 540 degrees C) into folds that plunge moderately to the west-southwest. The characteristic remanence clearly predates this early folding and is therefore primary; the Fisher parameter describing the concentration of the overall mean remanence direction improves from 3 to 32 when the site-mean directions are corrected by restoring the layering to estimated paleo-horizontal. All samples exhibit a magnetic anisotropy that is strong but nonuniform in orientation across the intrusion, and we show that it has no significant or systematic effect on the site-mean directions of remanence. At least some of the anisotropy derives from secondary magnetite formed during partial serpentinization. The mean paleomagnetic inclination (56 degrees +/- 10 degrees) corroborates paleomagnetic results from five coeval silicic plutons of the Canadian CoastPlutonic Complex to the south and southeast and implies 3000 km (+/- 1300 km) of poleward transport relative to the North American craton. Between mid-Cretaceous and middle Eocene time, the Insular superterrane and Coast Plutonic Complex shared a common paleolatitude history, with more poleward transport than coeval inboard terranes.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 15/07/20 alle ore 07:36:14