PROTEROZOIC LIP EVENTS, THEIR LINKS WITH ENVIRONMENTAL CRISES AND UTILITY AS NATURAL TIME MARKERS

Large Igneous Provinces (LIPs) are intraplate events characterized by voluminous and typically short duration mainly mafic magmatism (often > 1 Mkm3 and < 5 myr). They typically have a dramatic effect on the climate /environment. This is best demonstrated in the Phanerozoic where LIPs are linked to major and minor extinction events, and have a causal role in the specific kill mechanisms such as global warming, oceanic anoxia, oceanic acidification, glaciations, and toxic metal input (e.g. mercury).

The LIP record is best understood in the Phanerozoic. However, with U-Pb dating efforts over the past 20-30 years, and particularly with a recent industry-supported project focused on U-Pb dating of regional dolerite dyke swarms around the world (part of LIP plumbing systems) (e.g. Ernst et al. 2013, Lithos Special Issue, v. 174) our understanding of the global Proterozoic LIP record has signficantly improved.

Given the dramatic climatic/environmental impact of Phanerozoic LIP events (as mentioned above), it is expected that Proterozoic LIPs exerted a similar major influence on the Proterozoic environment which can be monitored by excursions in the compositions in sedimentary rocks of stable isotopes such as Sr, C, O, S, Os, Mo, Cr, and through other parameters such as Hg/TOC.

Furthermore, LIPs can be useful as proxies for chronostratigraphically defined Proterozoic and late Archean boundaries. Publications such as Okulitch (1987, 2002) and Bleeker (2004a,b) as well as the recent comprehensive review by Van Kranendonk et al. (2012) have argued for a revised Precambrian time scale based on natural chronostratigraphic boundaries (in some cases correlated with LIPs) to replace the current chronometric scale (that uses round numbers). Ideally boundaries should be placed at key events or transitions in the stratigraphic record (to establish ‘golden spikes’). Given their potential severe global environmental impacts LIPs can represent proxies for such boundaries. As a contribution toward the identification of appropriate natural boundaries, the current Proterozoic LIP record is summarized in terms of parameters relevant to their potential environmental effect. LIPs at 2500-2450, 2100, 2060, 1880, 1790-1750, 1525-1500, 1460, 1380, 1270, 1110, 825, 720, and 615-560 Ma are of particular significance.