Constraining the timescales of mafic magmatism of the Central Karoo Large Igneous Province using high precision U-Pb zircon geochronology

Abstract

Recent U-Pb high-precision geochronological studies have shown rapid emplacement of the intrusive doleritic component of the Karoo Large Igneous Province (KLIP) in Southern Africa. However, these studies focused on a relatively small geographic and altitudinal region of the KLIP. Additionally, the timing of initiation of extrusive volcanism, preserved in the Drakensberg-Lesotho highlands and its relationship to the intrusive suite, has only been imprecisely constrained by Ar-Ar dates. Here, we present new high-resolution U-Pb zircon ages on dolerite sills and dykes from across the central eastern Karoo Basin (South Africa) at elevations between mean sea level and 1 560 m, as well as U-Pb detrital zircon data that can be used to estimate the maximum age of volcaniclastic deposition near the base of the extrusive component of the KLIP. Dolerite samples were taken across two areas: (1) thick dykes exposed along the coast of the Indian Ocean to ~1 600 m flanking the Drakensberg Escarpment in the Eastern Cape; and (2) sills between 20 and 220 m below surface, in a borehole core within the interior of the Karoo Basin, 400 km hinterland from the coastline. Our estimated dolerite emplacement ages span a range of ca. 80 thousand years (Kyr), between 183.122 ± 0.029/-0.061 and 183.042 ± 0.042/-0.072 million years ago (Ma), and fall within the 331 +60/-54 Kyr age range previously established for magmatism related to the KLIP, despite the marked increase in sampling coverage in terms of area and altitude in this study. Therefore, KLIP geochronology is consistent with other LIPS such as the Siberian and Deccan Traps that supports the hypothesis of rapid emplacement timescales (<1 Myr). Additionally, these data are consistent with, but better delineate that the KLIP in southern Africa appears to be ca. 500 Kyr older than the main phase of magmatism in the Ferrar LIP of Antarctica. Detrital zircons from the basal volcanic sequence of the Drakensberg Group exhibit age peaks at ca. 1 and 0.5 Ga, typical of the surrounding Namaqua-Natal and Pan-African basement rocks, as well as younger peaks at ca. 260 and 200 Ma that likely relate to source provenances from south-western Gondwana and reworking of the Karoo Supergroup sedimentary rocks. High-precision U-Pb dates of the youngest zircon grains result in a maximum depositional age for the basal pyroclastics of 185.25 ± 0.25 Ma, allowing for a ca. 2 Myr offset with the intrusive Karoo dolerite suite.

Identifying crustal contributions in the Patagonian Chon Aike Silicic Large Igneous Province

“…The temporal and spatial overlap with the continental Karoo and Ferrar mafic large igneous provinces (ca. 182–183 Ma; Burgess et al 2015 ; Greber et al 2020 ; Muedi et al 2022 ) led some authors to suggest that crustal melting occurred in response to extensive basaltic underplating, sourced from a nearby plume (e.g., Storey and Kyle 1997 ; Pankhurst et al 2000 ; Storey et al 2013 ). However, a significant mass input is not supported by radiogenic data (Fig.…”

Technical Note: Pb-loss-aware Eruption/Deposition Age Estimation

“…Over the past decade, such dispersion has become difficult to ignore in single-crystal U/Pb zircon (e.g., Wotzlaw et al, 2013) and more recently Ar/Ar sanidine (e.g., Ellis et al, 2017) age spectra from many felsic volcanics, precluding the use of traditional weighted mean age interpretations. Amongst other potential solutions, a Markov chain Monte Carlo approach for eruption age estimation from dispersed age spectra in volcanic samples (Keller et al, 2018), and analogously saturation/emplacement/solidus age estimation in plutonic samples (Ratschbacher et al, 2018) has recently become relatively widely applied to overdispersed U/Pb zircon (Griffis et al, 2019;Schoene et al, 2019;Liao et al, 2020;MacLennan et al, 2020;Griffis et al, 2021;Al-Suwaidi et al, 2022;Muedi et al, 2022), U/Th zircon (Popa et al, 2020;Cisneros de León et al, 2021, and Ar/Ar sanidine (Deino et al, 2019;van Zalinge et al, 2022) datasets in volcanic contexts, as well as U/Pb zircon (Kinney et al, 2021(Kinney et al, , 2022Pamukcu et al, 2022) and U-Th/Pb monazite (Pye et al, 2022) in plutonic contexts.…”

High-Precision U-Pb Geochronology of an Ignimbrite Flareup in a Silicic Large Igneous Province (Chon Aike, Patagonia)

“…Jurassic paleo-reconstruction of southwest Gondwana. Jurassic magmatism during this period includes the felsic volcanic eruptions of the Chon Aike Silicic Large Igneous Province (CASP) and the contemporaneous mafic Karoo and Ferrar Large Igneous Provinces (e.g.,Antoine et al, 2022;Burgess et al, 2015;Gaynor et al, 2022a;Muedi et al, 2022). CASP U-Pb geochronology from 26 publications reveals differences in the spatio-temporal progression through time (references provided in ST3).The eastern portion of the SW Gondwana margin (Patagonia and the Antarctic Peninsula) records a protracted history of magmatism (ca.…”