Three belts of supracrustal metamorphic pendants are preserved within Jurassic to Tertiary plutons of the Coast Mountains between Prince Rupert and Bella Coola, British Columbia. On the basis of their Nd and Sr isotopic signatures, lithologic characteristics, and U-Pb detrital zircon ages, these supracrustal metamorphic rocks are interpreted to represent two belts of continental margin rocks separated by a narrow belt of rocks belonging to the Alexander terrane. The easternmost belt, referred to as the Burke Channel assemblage, and the westernmost belt, referred to as the Banks Island assemblage, consist mainly of interbedded quartzite, marble, metapelite, and metavolcanic rocks. The Burke Channel assemblage represents a heterogeneous crustal fragment containing both juvenile mantle derived and crustally evolved isotopic signatures. The εNd (100 Ma) values of rocks belonging to the Burke Channel assemblage range from -10.3 to +6.6 and 87Sr/86Sr (100 Ma) values range from 0.70418 to 0.70791. The Banks Island assemblage rocks are more systematically continental in their isotopic signatures, with εNd (100 Ma) ranging from +0.5 to -9.9 and 87Sr/86Sr (100 Ma) ranging from 0.71178 to 0.71934. The central belt of supracrustal rocks includes a metaclastic sequence that is dominated by a granitoid clast metaconglomerate that can be traced from the Bella Coola region north into Porcher Island. On the basis of their lithologic characteristic and U-Pb geochronology, the central belt rocks were correlated with the Lower Devonian Karheen Formation of the Alexander terrane. The Nd isotopic signatures of these rocks support this correlation. Their εNd(t) values range from +2.2 to +6.9 and indicate that a significant fraction of these rocks is juvenile and mantle derived.
|Original language||English (US)|
|Number of pages||11|
|Journal||Special Paper of the Geological Society of America|
|State||Published - Jan 1 2000|
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