The mantle reference frame defined by stationary hotspots has been used to determine the positions and motions of continental and oceanic plates surrounding the Caribbean region from late Jurassic time (140 m.y.) to the present. First, the position of the Pacific plate and the Pacific-Farallon spreading ridge has been reconstructed using the ages and geometry of island and seamount chains emanating from Pacific hotspots. Then, by assuming symmetric spreading across the Pacific-Farallon ridge, the motion of the Farallon plate relative to the mantle has been calculated. This shows that the postulated oceanic plateau which may form the core of the present Caribbean plate could have been erupted onto late Jurassic to early Cretaceous oceanic lithosphere as the Farallon plate passed over the Galapagos hotspot, hypothesized to have been initiated in mid- to l ate Cretaceous time (100 to 75 m.y. B.P.). The thickened volcanic plateau collided with the Greater Antilles Arc, then filling the gap between South America and nuclear Central America, in late Cretaceous time (80 to 70 m.y. B.P.) and was not subducted; instead, subduction of the Farallon plate commenced behind the plateau. This buoyant, indigestible piece of oceanic lithosphere drove the Greater Antilles Arc northeastwards, accompanied by subduction of proto-Caribbean crust, until it collided with the Bahama platform in late Eocene time. Concomitantly, the trench and island arc which developed behind (southwest of) the plateau generated what is now a part of Central America. Subsequent westward subduction of Atlantic lithosphere beneath the Lesser Antilles Arc and continuing eastward subduction of oceanic lithosphere beneath Central America, together with transform faulting (left-lateral Cayman transform fault in the north, right-lateral strike-slip motion in and off Venezuela in the south) defined the present boundaries of the Caribbean plate.

It has been suggested that the Shatsky Rise oceanic plateau formation began simultaneously with a reorganization of spreading at a triple junction bordering the northern Pacific plate, and this coincidence has led to speculation about the connections between the two events. We present new marine geophysical data that constrain the seafloor spreading history of the Pacific-Izanagi-Farallon triple junction just before the birth of the Shatsky Rise. Bathymetric data reveal en echelon, abandoned spreading centers trending northwest-southeast located adjacent to the southwest flank of the Shatsky Rise. Magnetic anomalies and bathymetry are interpreted to indicate that segments of the Pacific-Farallon Ridge near the triple junction propagated northwest from chron M23 (153 Ma) to chron M22 (151 Ma) during a spreading ridge reorganization at the edge of a likely microplate. Our detailed examination of bathymetric and magnetic anomaly lineations also shows that the strike of the Pacific-Izanagi Ridge changed gradually on the west side of the triple junction around chron M22. Our observations indicate that the plate boundary reorganization began several million years before the formation of the Shatsky Rise, implying that the eruption of the plateau did not cause the reorganization.

ABSTRACT Interactions of oceanic plates with North America near northern California since the Late Cretaceous can be broadly characterized as follows. A general decrease is seen in the age of the consumed Farallon (Juan de Fuca) plate(s) with implied increased buoyancy and decreased bathymetry. Age estimates range from greater than 70 million years old at 60 Ma to less than 10 million years old later than about 20 Ma. Coincident with this decrease in age is a systematic deceleration in convergence. Late Cretaceous to Oligocene velocities were greater than 100 km/m.y. whereas Neogene velocities average less than 50 km/m.y. Except for the introduction of the northwesterly-directed Pacific plate within the last few million years, the Farallon plate(s) show a northeasterly azimuth implying nearly straight-on convergence assuming a northwesterly-oriented trench. The Kula plate may have been in contact within the region until about 50 Ma. If so, its velocities were faster (greater than 150 km/m.y.) and more northerly directed implying a right-lateral component of convergence. A more detailed view of the tectonic history of northern California reveals several additional features that imply important departures from the general scenario presented above. Escarpments in the oceanic plates related to significant age contrasts across fracture zones within the Farallon plate migrated northward along this margin. These include equivalents to the Sila, Sedna, Surveyor, and Blanco fracture zones within the Farallon plate. In addition, reorganizations along ridges and transforms of the Pacific-Farallon boundary likely created bathymetric irregularities that descended into nearby trenches. Other bathymetric structures associated with the original rifting within the Farallon plate to form the Kula plate may have interacted in the region sometime between 70 and 50 Ma. Local uplift and subsidence probably occurred in response to the impingement of these bathymetric features and may have had an effect on near-trench deformation, erosion, and deposition. Also, a complicated break-up of the Farallon plate in the late Tertiary further obscures the kinematics of Farallon-North America interactions. Approach and interaction of the Pacific plate in the area occurred in the last few million years which drastically changed the style of the active margin. Moreover, the Pacific plate probably changed motion between about 3 and 5 Ma resulting in a component of convergence along its contact with North America.

Reconstruction of the tectonic evolution of the Pacific basin indicates a direct relationship between intraplate volcanism and plate reorganizations, which suggests that volcanism was controlled by fracturing and extension of the lithosphere. Middle Jurassic to Early Cretaceous intraplate volcanism included oceanic plateau formation at triple junctions (Shatsky Rise, the western Mid-Pacific Mountains) and a diffuse pattern of ocean island volcanism (Marcus Wake, Magellan seamounts) reflecting an absence of any well-defined stress field within the Pacific plate. The stress field changed in the Early Cretaceous when accretion of the Insular terrane to the North American Cordillera and the Median Tectonic arc to New Zealand stalled migration of the Pacific-Farallon and Pacific-Phoenix ocean ridges, leading to the generation of the Ontong Java, Manahiki, Hikurangi, and Hess Rise oceanic plateaus. Plate reorganizations in the Late Cretaceous resulted from the breakup of the Phoenix and Izanagi plates through collision of the Pacific-Phoenix ocean ridge with the southwest margin of the basin and development of island arc–marginal basin systems in the northwestern part of the basin. The Pacific plate nonetheless remained largely bounded by spreading centers, and intraplate volcanism followed preexisting lines of weakness in the plate fabric (Line Islands) or resulted from fractures generated by ocean ridge subduction beneath island arc systems (Emperor chain). The Pacific plate began to subduct under Asia in the Early Eocene as inferred from the record of accreted material along the Japanese margin. Further changes to the stress field at this time resulted from abandonment of the Kula-Pacific and the North New Guinea (Phoenix)–Pacific ridges and from development of the Kamchatkan and Izu-Bonin-Mariana arcs, leading to the generation of the Hawaiian chain as a propagating fracture. The final major change in the stress field occurred in the Late Oligocene as a result of breakup of the Farallon into the Cocos and Nazca plates, which caused a hiatus in Hawaiian volcanism; initiated the Sala y Gomez, Foundation, and Samoan chains; and terminated the Louisville chain. The correlations with tectonic events are compatible with shallow-source models for the origin of intraplate volcanism and suggest that the three principal categories of volcanism, intraplate, arc, and ocean ridge, all arise from plate tectonic processes, unlike in plume models, where intraplate volcanism is superimposed on plate tectonics.

Current interpretations of Cretaceous tectonic evolution of the northwest Pacific trace interactions between the Pacific plate and three other plates, the Farallon, Izanagi, and Kula plates. The Farallon plate moved generally eastward relative to the Pacific plate. The Izanagi and Kula plates moved generally northward relative to the Pacific plate, with Izanagi the name given to the northward-moving plate prior to the Cretaceous normal polarity superchron and the name Kula applied to the postsuperchron plate. In this article I suggest that these names apply to the same plate and that there was only one plate moving northward throughout the Cretaceous. I suggest that the tectonic reorganization that has previously been interpreted as formation of a new plate, the Kula plate, at the end of the superchron was actually a plate boundary reorganization that involved a 2000 km jump of the Pacific–Farallon–Kula/Izanagi triple junction. Because this jump occurred during a time of no magnetic reversals, it is not possible to map or date it precisely, but evidence suggests mid-Cretaceous timing. The Emperor Trough formed as a transform fault linking the locations of the triple junction before and after the jump. The triple junction jump can be compared with an earlier jump of the triple junction of 800 km that has been accurately mapped because it occurred during the Late Jurassic formation of the Mesozoic-sequence magnetic lineations. The northwest Pacific also contains several volcanic features, such as Hawaii, that display every characteristic of a hotspot, although whether deep mantle plumes are a necessary component of hotspot volcanism is debatable. Hawaiian volcanism today is apparently independent of plate tectonics, i.e., Hawaii is a center of anomalous volcanism not tied to any plate boundary processes. The oldest seamounts preserved in the Hawaii-Emperor chain are located on Obruchev Rise at the north end of the Emperor chain, close to the junction of the Aleutian and Kamchatka trenches. These seamounts formed in the mid-Cretaceous close to the spreading ridge abandoned by the 2000 km triple junction jump. Assuming that Obruchev Rise is the oldest volcanic edifice of the Hawaiian hotspot and thus the site of its initiation, the spatial and temporal coincidence between these events suggests that the Hawaii hotspot initiated at the spreading ridge that was abandoned by the 2000 km jump of the triple junction. This implies a tectonic origin for the hotspot. Other volcanic features in the northwest Pacific also appear to have tectonic origins. Shatsky Rise is known to have formed on the migrating Pacific-Farallon-Izanagi triple junction during the Late Jurassic–Early Cretaceous, not necessarily involving a plume-derived hotspot. Models for the formation of Hess Rise have included hotspot track and anomalous spreading ridge volcanism. The latter model is favored in this article, with Hess Rise forming on a ridge axis possibly abandoned as a result of a ridge jump during the superchron. Thus, although a hotspot like Hawaii could be associated with a deep mantle plume today, it would appear that it and other northwest Pacific volcanic features originally formed as consequences of shallow plate tectonic processes.