GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 106-3
Presentation Time: 8:30 AM


BURGESS, Seth D., United States Geological Survey, Volcano Science Center, 345 Middlefield Rd, Menlo Park, CA 94025, BOWRING, Samuel A., Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 and MUIRHEAD, James D., Department of Earth Sciences, Syracuse University, Syracuse, NY,

Large igneous province (LIP) magmatism is likely the primary trigger of mass extinctions, as suggested by broad temporal coincidence and potential for massive greenhouse gas release. However, a striking disparity between the duration of LIPs and mass extinctions complicates the simple cause-and-effect link. Duration disparity is highlighted by, but not unique to the end-Permian mass extinction, which occurred on a decamillenial timescale, and the Siberian Traps LIP, which occurred over ~1 Myr. This disparity begs the questions: If LIP magmatism is the primary trigger of mass extinctions, then (1) which magma fraction drove biosphere collapse, and (2) what trait of the qualifying fraction distinguishes it from the total LIP volume? The responsible volume must be erupted/intruded demonstrably prior and in close temporal proximity to the onset of mass extinction. Furthermore, this magma volume likely exhibits a unique attribute(s), such as eruption/intrusion tempo and/or style, timing relative to extinction, chemistry, volatile content, host rock composition, or some combination of these.

Recent datasets permit assessment of these questions, as the onset, duration, and tempo of coupled mass extinction and LIP events are well constrained, as is the temporal relationship between magmatism, global chemical cycles, and the biosphere. Here we focus on the end-Permian couplet, wherein the initial phase of LIP magmatism was characterized by primarily effusive eruptions, which generated ~2/3 of the total extrusive volume and began ~300 kyr prior to the onset of extinction. Extrusion halted for ~500 kyr during and after the mass extinction event. A dearth of shallow sills existed prior to the onset of mass extinction, but widespread sill intrusion coincided with cessation of extrusive magmatism and onset of mass extinction, continuing unabated for ~500 kyr. Given these associations, we posit that the thick LIP lava section provided a lithospheric barrier to magma ascent, thereby shifting the primary emplacement mechanism from extrusion to intrusion. This change significantly increased the volume of volatile-rich sediments with which LIP magmas were in contact. Massive volumes of greenhouse gases generated and released via contact metamorphism subsequently drove atmospheric change and biosphere collapse.