Arc eruptions deliver ‘ � rst blow ’ in the pulsed end-Permian mass extinction


 Brief pulses of intense magmatic activity (flare-ups) along convergent margins represent drivers for climatic excursions that can lead to major extinction events. However, correlating volcanic outpouring to environmental crises in the geological past is often difficult due to poor preservation of volcanic sequences. Herein, we present a high-fidelity, CA-TIMS U–Pb zircon record of an end-Permian flare-up event in Eastern Australia, that involved the eruption of >39,000–150,000 km3 of silicic magma in c. 4.21 million years. A correlated high-resolution tephra record (c. 260–249 Ma) in the proximal sedimentary basins suggests recurrence of eruptions from the volcanic field in intervals of ~51,000–145,000 years. Peak eruption activity at 253 Ma is chronologically associated with the pulsed stages of the Permian mass extinction event. The ferocity of the 253 Ma eruption cycle in Eastern Australia is identified as a driver of greenhouse crises and ecosystem stress that led to the reduction in diversity of genera and the demise of the Glossopteris Forests. Simultaneous global continental margin arc flare-up events could thus present an additional agent to trigger greenhouse warming and ecosystem stress that preceded the catastrophic eruption of the Siberian Traps.

silicic eruptions on the planet and can attribute appreciable outpouring of gases (CO 2 , H 2 O and CH 4 ) 6, 7,9 , understanding their periodicity and eruption volume is of crucial importance. This is particularly so during periods of global climatic and environmental instability, such as at the end of the Permian.
Eastern Australia Permian are-up A high-delity record of arc magmatism is presented from the Permian to Triassic margin in Eastern Australia (Figs 1 & 2). New high-precision Chemical Abrasion Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-TIMS) U-Pb zircon ages were measured on nine volcanic deposits and three representative coeval granites. The weighted mean 206 21 . The c. 290-280 Ma peak is related to back-arc extension and crustal reworking 22 . The Permian-Triassic event is associated with increasing mantle input to form the prominent batholith 23 . A voluminous sequence (Fig 3) of silicic ignimbrite sheets totalling thicknesses of 6.5-8 km is also preserved at this time over a broad surface expression supporting the estimated high magma uxes 18-20 . The deposits are consistent with a ratio of volcanic to plutonic material of 1:1 to 1:14.
It is less clear how representative the higher than typical ratios observed in arcs (1:2 to 1:30) 12 are in the context of preservation of igneous rock. However, the ratios are consistent with inferences from modern extending arcs 14 that preserve thick piles of volcanic strata in a setting similar to that of Eastern Australia in the Permian (Fig. 3a).
The volcanic eld preserves 4-8 distinct calderas which span an eruption period of c. 257.54 to 253.34 Ma (Fig. 2). The thickness of each volcanic member varies between 500-4000 m based on mapped relationships or geophysical observations 18-20 . The distribution is consistent with the eruption of at least 39,000 km 3 from three centres that migrated over time (Fig. 2). Initial volcanism occurred in the Western Belt involving ~22,750 km 3 of caldera in ll over c. The structural relationships of the ignimbrite sequence ( Fig. 2) are consistent with it being draped over an undulating topography, with erosion of the pile or the volcanic detritus occurring between individual eruptions 18, 19 . Most of the overburden to the youngest volcanic end-members appears to have been lost, consistent with predictions of ~3-4 km of denudation on the New England Tablelands in the last 100 million-years 24 . The volcanic deposits are also truncated in their original extent in all cardinal directions by dissection of the New England Tableland, particularly along the Great Escarpment to the east and the Peel Fault to the south and west (Fig. 2) 22 . Together these relationships suggest that the preserved volcanic material only records part of the duration of volcanism and is a minimum estimate for the eruption volume. Based solely on the preserved aerial extent of deposits across the entire volcanic eld, the eruption volume of the Wandsworth Volcanic Group is 150,000 km 3 (Fig. 2a). Although, this estimate does not account for the ~3-4 km of erosion and the amount of ash or other eruptive material that was not preserved near the primary volcanic centres, or in the adjacent Permian basins. . The total volumetric output from the tephra is less certain, but high-density layers at c. 254-252 Ma have total thicknesses of >100 m across the entire Sydney and Bowen Basin (60,000-64,000 km 2 each) 25,27 . Geochemical ngerprints of these events are consistent with contiguous and prolonged volcanism from the same, or similar rhyodacite to rhyolite sources that match those identi ed in the New England region 30,31 . The large dispersive extent of tephra and their general thicknesses is consistent with super-eruptions blanketing the majority of Eastern Australia in ash-fall and debris over an area of at least 950,000 km 2 consistent with eruptions volumes of >150,000 km 3 (Fig. 2).

Sources of silicic eruptions
The only prominent local source of silicic ash in Eastern Australia is the temporally correlated Wandsworth Volcanic Group and their spatially associated granites in the southern New England Orogen. Although, along arc extensions in northern Queensland are inferred to be additional contributors, particularly into the Bowen and Galilee basins, they lack prominent exposed volcanic sequences due to partial or complete erosion 32 31 . The prominence of resurgent granitic magmatism around the Eastern Belt and the occurrence of thick ignimbrite deposits (Emmaville and Dundee) is consistent with this region representing the key focal point of magmatism that spanned the end-Permian interval (Fig. 2).
A second period of higher-density tephra preservation occurs at 255 and 257 Ma in the surrounding Permian sedimentary basins. These ash layers match the ages of the ignimbrite deposits from the Southern and Western Belt of the Wandsworth Volcanic Group (Fig. 4). The volcanic events are less extensive in the tephra-record and are mostly focused in the Gunnedah, Sydney and southern portions of the Bowen basins suggesting a sustain period (c. 2 Myr) of high-volume eruptions 25,31 .
Globally, the commonality of arc magmatism at the end of the Permian is consistent with similar eruption-styles occurring concurrently along the margins of the supercontinent Pangea 7,8 . Synchronous are-up peaks at c. 255-250 Ma have been identi ed throughout South America, Antarctica, and China ( Fig. 1) [33][34][35][36] . These include the estimated 1.3x10 6 km 3 of silicic volcanism from the Choiyoi province in South America and Antarctica that is inferred to have contributed to greenhouse warming near the end-Guadalupian event 34 . Altogether global arc volcanism at the end of the Permian Period would have increased the total volcanic gas output, including the heightened production of greenhouse gasses 7,8 .

Super-eruptions and the end-Permian extinction
The end-Permian mass extinction is inferred to have transpired in several pulses [37][38][39] , plausibly initiated by a series of climatic perturbations preceding the actual Permian-Triassic boundary currently dated at 251.90 ± 0.10 Ma (Fig. 4) 40,41 . The eruption of extensive ood basalts as part of the Siberian Traps is considered to have had the greatest in uence on climatic perturbations during the period of c. 252.3-251.9 Ma (Fig. 4) 3,4 . However, it has been argued that multiple causative agents contributed to the periodic demise of biota and the reduction of diversity from c. 258 until 254 Ma (Fig. 4) 47 , have less severe extinction events before the delineated end Permian extinction horizon (Fig. 4) 28,48-51 . A series of greenhouse crises have been identi ed from palynological and geochemical proxies in the high-latitude Sydney Basin, consistent with a period of climatic variability from c. 265 Ma to the beginning of the Triassic (Fig.   4) 48,52,53 . The Eastern Australia are-up, and the along-strike extensions throughout Pangea present as compelling agents to some of these cycles of greenhouse conditions 54 (Figs 1 & 4). Although, until now the precise timing, vast quantitative scale, and extent of these eruptions in Eastern Australia has remained speculative.
Eruptions in Eastern Australia peaked at c. 254-252. 5 Ma, corresponding to a negative excursion in local carbon isotopic ratios (Fig. 4) 25 . This event marks the initiation of multiple end-Permian greenhouse crises (Fig. 4), involving perturbations in temperature, atmospheric CO 2 and rainfall in eastern Australia 52 . The ultra-Plinian (>1000 km 3 ) eruptions of the Emmaville (Fassifern Tuff), Dundee (Awaba Tuff) and the Yarrabee Tuff directly correspond temporally to identi ed greenhouse crises 52,55 , all of which pre date the Siberian Traps and the penultimate end Permian extinction. Additional Triassic greenhouse crises correspond to renewed volcanism associated to the Garie Tuff (Fig. 3b).
Multiple local environmental crises are likely to have been exacerbated by both the short-and longer-term consequences of catastrophic eruptions. These would include the initial cooling associated with the albedo effect of ash, followed by the prolonged greenhouse forcing related to the vast emission of volcanic aerosols 10 . Extensive drought, forest res and higher atmospheric carbon are inferred at this time based on pollen records from the intervening sedimentary layers to the tephra that correspond to the volcanic sequence (Fig. 3b) 28 . Generally, the c. 254-252 Ma period marks a signi cant change from cold glaciated conditions to progressive warming in Australia as well as globally (Fig. 4)    Identi ed Eastern Australia greenhouse crises52 are shown with extinction intervals based on oral species47. The thickness of the symbology encompasses the uncertainty on each age date. Eastern Australia are-up and the end-Permian mass extinction. The age distribution of volcanism in Eastern Australia at 260-247 Ma in relation to global magma activity based on zircon age systematics59. Identi ed Eastern Australia greenhouse crises52 are corrected for age systematics25 and associated with oral species demise28,47,48. Carbon isotope curves from marine carbonates in South China43, terrestrial organic material from eastern Australia Basins25, Genera diversity curves from Paleobiology database and sea surface temperature estimates based on conodont Oxygen isotopes37,38, 44