Pyroxene ⁴⁰Ar/³⁹Ar Dating of Basalt and Applications to Large Igneous Provinces and Precambrian Stratigraphic Correlations

Abstract

Correlations within and between Precambrian basins are heavily reliant on precise dating of volcanic units (i.e., tuff beds and lava flows) in the absence of biostratigraphy. However, felsic tuffs and lavas are rare or absent in many basins, and direct age determinations of Precambrian basaltic lavas have proven to be challenging. In this paper, we report the first successful application of 40Ar/39Ar dating to pyroxene from a Neoproterozoic basalt unit, the Keene Basalt in the Officer Basin of central Australia. 40Ar/39Ar analyses of igneous pyroxene crystals yielded an age of 752 ± 4 Ma (mean squared weighted deviation = 0.69, p = 72%), which is underpinned by 40Ar/39Ar plagioclase age (753.04 ± 0.84 Ma) from the basalt. This age is significant because the Keene Basalt is one of the very few extrusive igneous rocks identified within the Neoproterozoic successions of central Australia and is potentially an important time marker for correlating the Neoproterozoic stratigraphy within, and beyond, the central Australian basins. Our geochronological and geochemical data show that the Keene Basalt, which is characterized by enriched elemental and Nd‐Pb isotopic signatures, is strikingly similar to, and coeval with, the 755 ± 3 Ma Mundine Well Dolerite in northwestern Australia. Here we suggest that both are part of the same large igneous province (~6.5 × 105 km2) related to breakup of the supercontinent Rodinia. This study demonstrates the potential of pyroxene 40Ar/39Ar geochronology to date ancient flood basalts and to provide pivotal time constraints for stratigraphic correlations of Precambrian basins.

Interpreting and reporting 40Ar/39Ar geochronologic data

“…(5) 40 Ar/ 39 Ar analysis of nontraditional phases: Recent advances in our understanding of 40 Ar diffusion in minerals not traditionally used in 40 Ar/ 39 Ar chronometry, coupled with analytical advances that permit analysis of minerals that are poor in potassium, are rapidly expanding the spectrum of geologic questions that can be addressed. For example, 40 Ar diffusion data for pyroxenes (Cassata et al, 2011) provide new opportunities to use these minerals for the 40 Ar/ 39 Ar dating of mafic and ultramafic rocks (Ware and Jourdan, 2018;Konrad et al, 2019;Zi et al, 2019) and may provide more robust indications of the crystallization ages for weakly metamorphosed or hydrothermally altered samples than more familiar 40 Ar/ 39 Ar chronometers. The 40 Ar/ 39 Ar analyses of K-rich metasomatic and hydrothermal alteration phases (e.g., alunite, jarosite; Vasconcelos et al, 1994;Ren and Vasconcelos, 2019b) and 40 Ar/ 39 Ar dating of fluid inclusions via mechanical crushing (e.g., Xiao et al 2019) have become more commonplace.…”

What Is the Main Factor Controlling the Sukadana Basalt in the Sumatra Back Arc?

“…There is a possibility that the normal fault in the Sukadana basalt is a reactivated pre-existing fault. Furthermore, we believe that the presence of the Sukadana basalt on the surface is controlled by normal faults because the most likely structure for magma to emerge at the surface is an extensional fault [Ayalew et al, 2018;De Souza et al, 2013;Faccenna et al, 2010;Shahraki, 2013;Wang et al, 2015;Yan et al, 2018;Zi et al, 2019].…”

The distribution of vesicular structures in Sukadana Basalt, East Lampung, Indonesia, and its significance for the geological structure interpretation

“…When related to the type of fault, the type of fault that most likely allows magma to rise to the earth's surface is a normal fault. This has been evident from various studies in the world related to the emergence of basalt magma on the earth's surface [11][12][13][14][15][16][17]. Therefore, the Sukadana basalt is present on the earth's surface due to normal fault activity, which is strongly expected to be Quaternary.…”