Evolution of Triple Junctions

Recognition on space photographs of structural elements of Baja California

“…The Bahia Concepcion-La Paz fault -if its character and continuity have been correctly inferred-may represent motion between the North American and western Pacific tectonic plates before the mouth of the present Gulf of California began to open by separation of the Cabo San Lucas terrain from mainland Mexico. (See Larson and others, 1968;McKenzie and Morgan, 1969. ) …”

Gravity in the junction between the Japanese and the Izu-Bonin Islands.

“…In the following section, the authors attempt to explain the phenomena in the trench or arc junction from the plate tectonic standpoint. 3.2 Relationship between gravity anomalies and tectonics of arc junctions MCKENZIE and MORGAN (1969) pointed out the existence of a T-T-T(a) type triple junction ('unstable' triple junction) at the intersection of the Japan Trench, the Izu-Bonin Trench and the Nankai Trough. But, since the connection of the Nankai Trough with the other two plate boundaries was not properly explained, SUGIMURA (1972) proposed a more realistic boundary between the Eurasia and the Philippine-Sea plates by incorporating the Sagami and the Suruga Troughs into the Nankai Trough.…”

The Tooth of Time: The North American Cordillera from Tanya Atwater to Karin Sigloch

“…Given westward drift of North America as the Atlantic opened, the San Andreas was in fact predestined to grow from a point by the large separation in PacificFarallon spreading axes north and south of the Mendocino Fracture Zone (Fig. 6), confidently inferred from the magnetic lineations of the Northeast Pacific (McKenzie and Morgan 1969;Atwater and Menard 1970). Assuming that coast-parallel motion of the Pacific plate relative to North America had persisted since mid-Cenozoic time (her preferred model), Tanya's reconstruction (Atwater 1970) implied that Farallon plate subduction ceased and San Andreas faulting first began opposite Guaymas (Mexico), after which its intersection with the Mendocino transform fault swept rapidly northward to its present location off Cape Mendocino (westernmost California), while its intersection with the East Pacific Rise inched southward toward Mazatlán (Fig.…”

“…The transformation of the continental margin from a convergent plate boundary to a strike-slip boundary would have occurred at any latitude when the spreading ridge met the subduction zone, resulting in their mutual destruction. This scenario was beautifully spelled out in principle by McKenzie and Morgan (1969), who named the ancestral third plate the Farallon plate (Fig. 3).…”