1984 Results of trans-Alaska crustal transect in Chugach Mountains and Copper River Basin, Alaska
The Trans-Alaska Crustal Transect (TACT) program, a multidisciplinary investigation of the continental crust and its evolution along the Trans-Alaska pipeline corridor was started by the USGS during 1984. Preliminary results of geologic, geophysical, and wide-angle reflection/refraction data obtained across the Chugach terrane (CGT) and the composite Wrangellia/Peninsular terrane (WRT/PET) suggest the following: (a) the CGT is composed of accretionary sequences that include, from south to north, Late Cretaceous schistose flysch, uppermost Jurassic to Early Cretaceous sheared melange, and Early(.) Jurassic blueschist/greenschist. (b) The CGT accretionary sequences have local broad, low-amplitude magnetic or gravity anomalies. (c) Seismic data show that the CGT along latitude 61/sup 0/N, by alternating high- (6.9-8.0. km/sec) and low-velocity layers is suggestive of multiple thin slices of subducted oceanic crust and upper mantle. (d) Mafic and ultramafic cumulate rocks along the south margin of the WRT/PET have strong magnetic and gravity signatures and are interpreted as the uplifted root of a Jurassic magmatic arc superimposed on a late Paleozoic volcanic arc. Magnetic data suggest that comparable rocks underlie most of the PET. (e) The Northdipping border Ranges fault (BRF) marks the suture along which the northern margin of the CGT was relatively underthrust at least 40 km beneath the WRT/PET. (f) Beneath the northern CGT and southern WRT/PET, a prominent seismic reflector (v = 7.7 km/sec), suggestive of oceanic upper mantle rocks, dips about 3/sup 0/N and extends from a depth of 12 km beneath the Tasnuna River to 16 km beneath the BRF, where the dip appears to steepen to about 15/sup 0/ beneath the southern margin of the PET.
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 5854694
- Report Number(s):
- CONF-8505215-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 69:4; Conference: AAPG-SEPM-SEG Pacific section meeting, Anchorage, AK, USA, 22 May 1985
- Country of Publication:
- United States
- Language:
- English
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