Which of the following statements best characterizes the geology of western North
America, starting in California and extending through British Columbia and up into
Alaska?
A) Divergent rifting creating deep, wide valleys with grabens
B) Collision of a massive subcontinent of old igneous and metamorphic rocks, resulting
in fold-and-thrust mountains that are still growing
C) Geologically distinct, microcontinent-sized fragments and terraces accreted to the
continent
D) Metamorphosed accretionary wedges
Which is denser: a 100-million-year-old oceanic lithosphere near a convergent
boundary, a 15-million-year-old oceanic lithosphere near a rift, or the upper part of the
asthenosphere?
A) A 15-million-year-old oceanic lithosphere
B) 100-million-year-old oceanic lithosphere
C) Upper asthenosphere
D) They all have the same density.