SUMMARY We use elastic block modelling of 126 GPS site velocities from Jamaica, Hispaniola, Puerto Rico and other islands in the northern Caribbean to test for the existence of a Hispaniola microplate and estimate angular velocities for the Gônave, Hispaniola, Puerto Rico‐Virgin Islands and two smaller microplates relative to each other and the Caribbean and North America plates. A model in which the Gônave microplate spans the whole plate boundary between the Cayman spreading centre and Mona Passage west of Puerto Rico is rejected at a high confidence level. The data instead require an independently moving Hispaniola microplate between the Mona Passage and a likely diffuse boundary within or offshore from western Hispaniola. Our updated angular velocities predict 6.8 ± 1.0 mm yr−1 of left‐lateral slip along the seismically hazardous Enriquillo‐Plantain Garden fault zone of southwest Hispaniola, 9.8 ± 2.0 mm yr−1 of slip along the Septentrional fault of northern Hispaniola and ∼14–15 mm yr−1 of left‐lateral slip along the Oriente fault south of Cuba. They also predict 5.7 ± 1 mm yr−1 of fault‐normal motion in the vicinity of the Enriquillo‐Plantain Garden fault zone, faster than previously estimated and possibly accommodated by folds and faults in the Enriquillo‐Plantain Garden fault zone borderlands. Our new and a previous estimate of Gônave‐Caribbean plate motion suggest that enough elastic strain accumulates to generate one to two Mw∼ 7 earthquakes per century along the Enriquillo‐Plantain Garden and nearby faults of southwest Hispaniola. That the 2010 M= 7.0 Haiti earthquake ended a 240‐yr‐long period of seismic quiescence in this region raises concerns that it could mark the onset of a new earthquake sequence that will relieve elastic strain that has accumulated since the late 18th century.

SUMMARY We use block modelling of GPS site velocities from Jamaica and nearby islands, including Hispaniola, to test alternative plate boundary geometries for deformation in Jamaica and estimate slip rates along the island's major fault zones. Relative to the Caribbean Plate, GPS sites in northern Jamaica move 6.0 ± 0.5 mm yr−1 to the WSW, constituting a lower bound on the motion of the Gônave microplate across its southern boundary in Jamaica. Obliquely convergent motion of all 30 GPS sites on and near Jamaica relative to the island's ∼E–W‐trending strike‐slip faults may be partitioned into 2.6 ± 0.6 mm yr−1 of ∼N–S shortening across submarine faults south of Jamaica and 5–6 mm yr−1 of E–W motion. Guided by geological and seismic information about the strikes and locations of faults in Jamaica, inverse block modelling of the regional GPS velocities rejects plate boundary configurations that presume either a narrow plate boundary in Jamaica or deformation concentrated across a restraining bend defined by the topographically high Blue Mountains of eastern Jamaica. The best‐fitting models instead place most deformation on faults in central Jamaica. The 4–5 mm yr−1 slip rate we estimate for the Plantain Garden fault and Blue Mountain restraining bend of southeastern Jamaica implies significant seismic hazard for the nearby capital of Kingston.

The northern Owyhee Mountains of southwestern Idaho contain granitoid rocks that are the same age as the Cretaceous western border zone of the Idaho batholith to the north of the Snake River Plain. They contain a well-developed and consistently oriented 020° foliation, zircon yielding U-Pb dates of ca. 160-48 Ma, and initial 87 Sr/ 86 Sr isotopic compositions that show a steep west-to-east transition in values from 0.704 to 0.708 over a distance of ~30 km. The rocks of the northern Owyhee Mountains are interpreted to be the southward continuation (Owyhee segment) of the western Idaho shear zone. Similar to a well-studied section of the western Idaho shear zone by McCall (McCall segment), the Owyhee segment displays steep foliation and lineation orientations, deformation of 98-90 Ma plutons, steep Sr isotopic gradients, and syntectonic tonalite intrusions. However, the Owyhee segment has three major differences from the McCall segment: (1) signifi cantly less well-developed solid-state strain fabric foliations; (2) trend of 020° rather than 000°; and (3) a wider transition zone in initial Sr ratios from 0.704 to 0.708. We present a simple tectonic model to explain these differences, assuming a 20° along-zone difference in the initial orientation of the western margin of the Laurentia, a rigid-body collision, homogeneous material behavior, and transpressional kinematics. For the Owyhee segment, the model predicts a lower oblique-convergence angle, less convergent displacement, more dextral transcurrent displacement, and an overall lower fi nite strain relative to the McCall segment.

The Bogota Peninsula shear zone has been interpreted as a paleotransform fault in the mantle section of the New Caledonia ophiolite. New, detailed fi eld measurements document the rotation of foliation, lineation, and pyroxenite dikes across a 50-km-wide region. Deformation intensity recorded by folding and boudinage of dikes increases toward a central, 3-km-wide mylonitic zone. We used several additional methods to characterize fabric patterns across the shear zone. The shape-preferred orientation of orthopyroxene grains, computed from outcrop tracings, closely parallels fi eld fabrics, with increased alignment and fl attening near the center of the shear zone. The lattice-preferred orientations of olivine are consistent with high-temperature fabrics; the a axes within the mylonitic core were used to constrain the orientation of shear zone boundaries. Seismic anisotropy calculations, based on the lattice-preferred orientation of olivine, indicate 5%-11% shear-wave anisotropies, with increased values in the center of the shear zone. The magnetic silicate fabric in the rocks, determined from anisotropy of magnetic susceptibility techniques, broadly matches fi eld fabrics but provides less consistent information across the shear zone than other fabric methods. This suite of fi eld and laboratory data provides a unique and detailed view of strain and fabric patterns across a shear zone in oceanic mantle lithosphere. Because the primary mantle fabrics seem to be related to the present distribution of ophiolitic rocks in New Caledonia, we propose that ophiolite obduction and Neogene extension may have been controlled by preexisting fabrics and structures in the oceanic lithosphere.

We present new shear‐wave splitting measurements of SKS, SKKS, PKS, and sSKS phases from eight stations in the northern Caribbean. Prior to this work, shear‐wave splitting analysis of the northern Caribbean boundary was only evaluated at a station in Puerto Rico. Stations that lie within several tens of kilometers of microplate boundaries have mean fast polarization directions parallel to the boundary and have delay times greater than 1 s. Stations more than several tens of kilometers away from microplate boundaries show no evidence for an anisotropic upper mantle. Stations in Cuba and Jamaica have fast axes oriented ∼100° with delay times of ∼1.5 s, indicating that the east‐striking left‐lateral strike‐slip faults that define the north and south boundaries of the Gônave microplate continue into the upper mantle. A station located in Antigua, where the North America plate subducts beneath the Caribbean plate, has a high degree of splitting with the fast axis parallel to the trench. Based on our results, the deformation related to the presence of microplates in the northern Caribbean extends into the upper mantle.