| Popis: |
The pacific margin of North America is composed of many allochthonous terranes that accreted to the cratonal nucleus during Mesozoic and early Cenozoic time. More than 150 terranes have now been recognized, each of which is characterized by distinctive rock assemblages and geologic histories that differ markedly from those of their neighbors. These terranes are composed of scraps of island arcs, disrupted oceanic basins with abundant radiolarian chert, parts of seamounts, continental-rise prisms, and continental fragments, some of which seem to be of North American affinity. Combined paleomagnetic, paleobiogeographic, and lithologic data substantiate that some terranes have moved northward as much as several thousand kilometers; some terranes now at high latitudes may have been situated in the Southern Hemisphere during Triassic time. Tectonic effects during accretion include polyphase isoclinal folding, large-scale thrust and strike-slip faulting, development of penetrative metamorphic fabrics on a regio... |
