Abstract The Elan Bank microcontinent was separated from East India during the Early Cretaceous break-up. The crustal architecture and rifting geometry of East India and the Elan Bank margins document that the early break-up between India and Antarctica was initiated in the eastern portions of the Cauvery and Krishna–Godavari rift zones, and in the southern portion of Elan Bank. However, the westwards break-up propagation along the Krishna–Godavari Rift Zone continued even after the break-up in the overstepping portion of the Cauvery Rift Zone. Eventually, the western propagating end of the Krishna–Godavari Rift Zone became hard-linked with the failed western portion of the Cauvery Rift Zone by the dextral Coromandel transfer fault zone. Consequently, the break-up location between India and Antarctica shifted from its initial to its final location along the northern portion of the Elan Bank formed by the western Krishna–Godavari Rift Zone. The competition between the two rift zones to capture continental break-up and asymmetric ridge propagation resulted in a ridge jump and the Elan Bank microcontinent release.

Abstract The intracratonic, supra-subduction zone setting of the Thailand rift basins caused the rifts to evolve in several ways differently from other intracratonic rifts. Key differences include: widespread occurrence of low-angle normal faults; basin inversion alternating with rifting; diachronous initiation and cessation of rifting; rapid post-rift subsidence; and extensive, low-displacement post-rift faults. These characteristics are related to hot, weak continental lithosphere, rapid evolution of the plate boundaries and stresses during the Cenozoic, and the history of subduction and accretion. Low-angle normal faults impacted the Sirikit Field by controlling the location of fluvio-deltaic reservoirs interfingering lacustrine shales (source and seal). Basin inversion alternating with syn-rift section is detrimental to prospectivity of the southern half of the Phitsanulok Basin by destroying syn-rift structure, and halting hydrocarbon maturation early in the basin history. The diachronous timing of basin development resulted in large, gas-dominated hydrocarbon accumulations in the eastern Gulf of Thailand basins, but was detrimental for younger basins that lack the post-rift section, and the greater variety of petroleum systems and traps that post-rift basins offer. The extensive low displacement–length ratio post-rift faults form significant hydrocarbon traps in the Pattani and North Malay basins. They represent a structural style not usually found in post-rift basins.

The structural geometry of transfer and accommodation zones that relay strain between extensional domains in rifted crust has been addressed in many studies over the past 30 years. However, details of the kinematics of deformation and related stress changes within these zones have received relatively little attention. In this study we conduct the first-ever systematic, multi-basin fault-slip measurement campaign within the late Cenozoic Rio Grande rift of northern New Mexico to address the mechanisms and causes of extensional strain transfer associated with a broad accommodation zone. Numerous (562) kinematic measurements were collected at fault exposures within and adjacent to the NE-trending Santo Domingo Basin accommodation zone, or relay, which structurally links the N-trending, right-stepping en echelon Albuquerque and Española rift basins. The following observations are made based on these fault measurements and paleostresses computed from them. (1) Compared to the typical northerly striking normal to normal-oblique faults in the rift basins to the north and south, normal-oblique faults are broadly distributed within two merging, NE-trending zones on the northwest and southeast sides of the Santo Domingo Basin. (2) Faults in these zones have greater dispersion of rake values and fault strikes, greater dextral strike-slip components over a wide northerly strike range, and small to moderate clockwise deflections of their tips. (3) Relative-age relations among fault surfaces and slickenlines used to compute reduced stress tensors suggest that far-field, ~E-W–trending σ 3 stress trajectories were perturbed 45° to 90° clockwise into NW to N trends within the Santo Domingo zones. (4) Fault-stratigraphic age relations constrain the stress perturbations to the later stages of rifting, possibly as late as 2.7–1.1 Ma. Our fault observations and previous paleomagnetic evidence of post–2.7 Ma counterclockwise vertical-axis rotations are consistent with increased bulk sinistral-normal oblique shear along the Santo Domingo rift segment in Pliocene and later time. Regional geologic evidence suggests that the width of active rift faulting became increasingly confined to the Santo Domingo Basin and axial parts of the adjoining basins beginning in the late Miocene. We infer that the Santo Domingo clockwise stress perturbations developed coevally with the oblique rift segment mainly due to mechanical interactions of large faults propagating toward each other from the adjoining basins as the rift narrowed. Our results suggest that negligible bulk strike-slip displacement has been accommodated along the north-trending rift during much of its development, but uncertainties in the maximum ages of fault slip do not allow us to fully evaluate and discriminate between earlier models that invoked northward or southward rotation and translation of the Colorado Plateau during early (Miocene) rifting.

Tascotal Mesa fault is the principal component of Tascotal Mesa transfer zone within the Rio Grande rift of Texas (USA) and Chihuahua (Mexico). Strata and structures along the zone attest to ~290 m.y. of tectonic and magmatic activity, from at least late Paleozoic time onward. The transfer zone comprises the Tascotal Mesa and newly documented Christmas Mountains–Grapevine Hills faults, as well as the Terlingua Creek pull-apart complex at the right step between those two dextral zones. Strike-slip (to ~1 km) and dip-slip (to ~735 m) displacements have occurred in the zone during the past 30–27 m.y.; young faults of the transfer zone displace mid-Pleistocene caliches. Stable isotope and palynologic data from travertines in the transfer zone indicate ascent of warm waters (25°–35 °C) along faults as recently as mid- to late Pleistocene time. Older, basement-rooted structural anisotropies are present in the Tascotal Mesa transfer zone but not all have been reactivated during Cenozoic rifting. Geophysically constrained physical models integrated with field data demonstrate that the Terlingua Creek pull-apart basin likely formed in cover strata that were detached from basement, as the orientations of surficial and buried basement structures differ markedly. Dip-slip displacement predominates on pull-apart faults, with significant dextral slip. Analysis of the role of the Tascotal Mesa transfer zone in Rio Grande rifting revealed that it and the flanking grabens (Presidio to the northwest; Redford to the southeast) are all parts of the Border Corridor transform zone. This transform zone interconnects rift segments from Mesilla graben to the Sunken Block and includes both transfer zones and grabens. Right-transtensional deformation, as manifested in historic earthquakes, accounts for differing orientations of transform (northwest) versus rift (north) grabens. Petrographic and geochronologic data indicate ascent of lavas of rift geochemical character in both the Tascotal Mesa transfer zone and the Border Corridor transform zone from ca. 30 Ma onward. K-Ar ages were determined for basalt (24.73 ± 1.96 Ma) and trachyte (25.42 ± 0.64 Ma) emplaced within the Tascotal Mesa transfer zone. Magmatism is bimodal; olivine basalt and/or hawaiite predominates. Basalts at the junctions of rift grabens and the Border Corridor transform zone entrain mantle and lower-crustal xenoliths.