The role of the Polochic Fault as part of the North American and Caribbean Plate boundary: Insights from the infill of the Lake Izabal Basin

Abstract

The Lake Izabal Basin in Guatemala is a major pull-apart basin along the sinistral Polochic Fault, which is part of the North American and Caribbean plate boundary. The basin infill contains information about the tectonic and sedimentological processes that have imparted a significant control on its sedimentary section. The inception of the basin has been linked to the relative importance of the Polochic Fault in the tectonic history of the plate boundary; yet, its sedimentological record and its inception age have been poorly documented. This study integrates diverse datasets, including industry reports, well logs and reports, well cuttings, vintage seismic data, outcrop observations and geochronological data to constrain the initial infill and age of inception of the basin. The integrated data show that during the Oligocene-Miocene, a marine carbonate platform was established in the region which was later uplifted and eroded in the early Miocene. The fluvial-lacustrine deposits above this carbonate platform are part of the initial infill of the basin and are constrained with zircon weighted-mean 206 Pb/ 238 U ages of 12.060 ± 0.008 from a volcanic tuff ~30 m above the unconformity. Sandstone, mudstone and coal dominate the interval from 12 to 4 Ma, with an increase in conglomerate correlating to the uplift of the Mico Mountains and San Gil Hill at 4 Ma. Fault switch activity between the Polochic and Motagua faults has been hypothesized to explain total offset along the Polochic Fault and the geologic and geodetic slip rates along the two faults. The 12 Ma age determined for the initial infill of the basin confirms this hypothesis. Consequently, our study confirms that at ~12 Ma the Polochic Fault served as the main fault of the plate boundary with inferred slip rates ranging from 13 to 21 mm/yr with a strong possibility that the Polochic Fault was, at some point between 15 Ma and 7 Ma, the only active fault of the plate boundary. The results of this study show that tectonic records preserved in sediments of strike-slip basins improve the understanding of the relative significance of individual faults and the implications with respect to strain partitioning throughout its tectonic history.

New estimates of the magnitude of the sea-level jump during the 8.2 ka event

“…(1) An abrupt drop in the lake spillway position caused by tectonic movement. Lake Izabal is situated in a pull-apart basin along the North American-Caribbean plate boundary (Bartole et al, 2019;Obrist-Farner et al, 2020). It is unlikely, however, that a single or multiple tectonic events could have caused substantial vertical displacement without leaving physical evidence.…”

“…It is unlikely, however, that a single or multiple tectonic events could have caused substantial vertical displacement without leaving physical evidence. No fault scarps in the Lake Izabal area display evidence of recent vertical tectonic activity (Lodolo et al, 2009;Obrist-Farner et al, 2020). Furthermore, the spillway is currently located on the footwall of the main fault, which further reduces the likelihood of downward displacement, and El Golfete is located in a region of transpression as evidenced by the presence of the Mico Mountains (Fig.…”

“…Furthermore, the spillway is currently located on the footwall of the main fault, which further reduces the likelihood of downward displacement, and El Golfete is located in a region of transpression as evidenced by the presence of the Mico Mountains (Fig. 1; Obrist-Farner et al, 2020).…”

Active faulting in the Beagle Channel (Tierra del Fuego)

“…Our analysis indicates that the BCFS also experienced deformation pulses following glacial recession, implying a wider It must be emphasized, however, that in many examples of transform systems along plate boundaries, relative motion between plates does not occur exclusively along a single, master fault, but is distributed over a more or less large deformation zone comprising several faults running sub-parallel to the main fault, as documented in other strike-slip tectonic environments similar to those of the South America-Scotia plate boundary (e.g. Lodolo et al, 2009;Obrist-Farner et al, 2020).…”

The triple junction of the North America, Cocos, and Caribbean plates. What we know, what we don’t

“…Once in continental Guatemala, the Swan Island fault zone becomes the Motagua-Polochic fault zone, a pair of large faults, with subsidiary smaller faults, that run roughly from east to west, concave to the north, while the Swan Island fault is slightly concave to the SSE. These are two left-lateral fault zones that extend for about 350 km, the Polochic to the north, the Motagua to the south (e.g., Bonis, 1967;1975;Muehlberger and Ritchie, 1975;Burkart, 1978;Burkart and Self, 1985;Franco et al, 2009;Authemayou et al, 2012;Obrist-Farner et al, 2020) (Figures 1 and 2). Some authors include the Jocotán-Chamelecón fault system, located south of the Motagua fault, as part of the plate boundary zone (e.g., Crane, 1965;Schwartz et al, 1979;Burkart and Self, 1985).…”