Accretion, subduction, and underplating along the southern Alaska continental margin
In 1984-1985 the Trans Alaska Crustal Transect (TACT) program completed geologic, seismic refraction, gravity, and magnetic studies along a 350-km-long corridor that extends northward from the Gulf of Alaska coast near Cordova to the Denali fault at the Richardson Highway. From south to north, this segment of the transect traverses: 1) part of the Prince William terrance (PWT), composed of an accreted Paleocene and Eocene deep-sea fan complex, oceanic volcanic rocks, and pelagic sediments; 2) the Chugach terrane (CGT) composed of a) accreted Late Cretaceous flysch and oceanic basaltic rocks, b) accreted and subducted (.) Late Jurassic to Early Cretaceous sheared melange, and c) subducted Early (.) Jurassic or older blueschist/greenschist; and 3) Wrangellia-Peninsular terranes (WRT/PET) consisting primarily of late Paleozoic intraoceanic andesitic arc rocks with associated mafic and ultramafic plutonic rocks, an overlying distinctive Triassic sedimentary and volcanic sequence, and superposed intrusive and extrusive magmatic rocks of the Jurassic Talkeetna arc. At the southern margin of both the CGT and WRT/PET, shallow high-velocity zones characterized by positive gravity and magnetic anomalies reflect uplift of mafic and ultramafic basement along these thrusts. The Contact and Border Ranges fault systems appear to merge into a subhorizontal low-velocity zone of uncertain origin that underlies the CGT and southern WRT/PET at 5-9 km depth. A few kilometers beneath the shallow low-velocity zone in a 30-km-thick stack of eight northward-dipping layers of alternating high and low velocity, interpreted as subducted and underplated mantle and oceanic crust rocks. Distribution of earthquake hypocenters suggests that active subduction involves at least the lowest two and possibly the lower four layers.
- Research Organization:
- Geological Survey, Menlo Park, CA (USA)
- OSTI ID:
- 6319653
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
Similar Records
Accretion and subduction tectonics in the Chugach Mountains and Copper River Basin, Alaska: initial results of the Trans-Alaska Crustal Transect
Thondhjemite of the Talkeetna Mountains: An unusually large low-K pluton in Alaska's Peninsular terrane
Related Subjects
ALASKA
CONTINENTAL MARGIN
PLATE TECTONICS
VOLCANIC ROCKS
GEOLOGIC FAULTS
GEOLOGY
GEOPHYSICAL SURVEYS
OCEANIC CRUST
SEISMIC EVENTS
SUBDUCTION ZONES
EARTH CRUST
FEDERAL REGION X
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
NORTH AMERICA
ROCKS
SURVEYS
TECTONICS
USA
580201* - Geophysics- Seismology & Tectonics- (1980-1989)
580100 - Geology & Hydrology- (-1989)