Final answer:
Magma generation due to decreasing pressure primarily occurs at divergent plate boundaries, where tectonic plates move apart, allowing the mantle to melt due to reduced pressure.
Step-by-step explanation:
Magma is generated due to decreasing pressure at divergent plate boundaries, where tectonic plates are moving apart from each other. This process is known as decompression melting and usually occurs at mid-ocean ridges, where the mantle beneath is exposed to lower pressures as the plates diverge. Transform plate boundaries involve lateral movement of plates against each other and do not typically result in magma formation; a passive continental margin is the transition between oceanic and continental lithosphere that is not an active plate margin and does not usually produce magma; impacts by meteorites can create intense heat and pressure leading to melting but not typically due to decreasing pressure; and finally, convergent plate boundaries typically generate magma due to the flux melting caused by water released from subducting plates, not due to decompression.