We investigate the NW-SE basement trends of the U.S. Midcontinent, often cited as Proterozoic in age. From a reduced-to-pole magnetic anomaly map, we map basement lineaments over an area of ~1.48 million km2. We compile published Ediacaran-Ordovician radiometric dates of intrusive rocks that suggest a deep crustal/mantle magma source for this time. Dolomite from one core provides one higher precision U-Pb date of 462 {plus minus}15 Ma and several lower precision dates that overlap this age range. Fluid inclusion, carbon, oxygen, and strontium isotope data indicate hot fluids were injected from deep in the basement relatively early in the Paleozoic. Even though the area has been structurally overprinted by late Paleozoic and later deformation, compilation of regional stratigraphic and structural data points strongly to widespread deformation in the latest Proterozoic to early Paleozoic. Taken together, these data indicate that the NW-SE basement trends are long-lived leaky transform faults associated with Iapetan rifting during the Ediacaran-Ordovician. These transform faults are interpreted as transtensional in part and leaky with respect to both magmatic emplacement and hot fluids from deeper in the basement. Our findings suggest a new model for the tectonic evolution of the U.S. Midcontinent, based on changing stress fields as subduction progresses south into Iapetus. This has implications for the origin of zones of weakness that are reactivated later, the distribution of aulacogens versus transforms, and the tectonic underpinnings of ore minerals deposited concurrently with the active faulting as well as oil and mineral deposits formed during their later reactivation.

Vietnam contains a complex series of faults coupled with a diffuse igneous province that has been active since the mid-Miocene. However, existing fault maps demonstrate little consensus over the location of Neogene basalt flows and relative ages of mapped faults, which complicates interpretations of tectonic model for the evolution of Indochina. This paper identifies discrete tectonic blocks within Vietnam and aims to define the Neogene-Recent tectonic setting and kinematics of south-central Vietnam by analyzing the orientation, kinematics, and relative ages of faults across each block. Fault ages and relative timing are constrained using cross-cutting relationships with dated basalt flows and between slickenside sets. Remote sensing results show distinct fault trends within individual blocks that are locally related to the orientations of the basement-involved block-bounding faults. Faults observed in the field indicate an early phase of dip-slip motion and a later phase of strike-slip motion, recording the rotation of blocks within a stress field. Faulting after the change in motion of the Red River Fault Zone is inferred, as faults cross-cut basalt flows as young as ~0.6 Ma. Strike-slip motion on block-bounding faults is consistent with rotation and continuous extrusion of each block within south-central Vietnam. The rotation of the blocks is attributed to the “continuum rubble” behavior of small crustal blocks influenced by extrusion-driven asthenospheric flow after the collision between India and Eurasia. We deduce a robust lithospheric-asthenospheric coupling in the extrusion model, which holds implications for other regions experiencing extrusion even in the absence of a free surface.

A document by Kirby Hobbs. Click on the document to view its contents.

This article provides a commentary about the state of integrated, coordinated, open, and networked (ICON) principles in Earth and Planetary Science Processes (EPSP) and discussion on the opportunities and challenges of adopting them. This commentary focuses on the challenges with current inclusive, equitable, and accessible science and highlights how research undertaken in the earth and planetary surface processes community currently benefit from and would be able to grow as a discipline with more directed implementation of ICON principles.