www.saltworkconsultants.com Salty MattersJohn Warren - Saturday April 13, 2019 Evaporite interactions with magma Part 3 of 3: On-site evaporite and major extinction events? Introduction 60 The previous two articles in this series Siberian Traps dealt with heating evaporites, vola- tiles expelled into the atmosphere, 50 and major biotal extinction events. Emeishan Traps I argued that short-term heating of 40 Deccan Traps a megaevaporite mass during em- Cental Atlantic (+ Yucatan bolide) placement of a Large Igneous Prov- 30 Magmatic Province ince (LIP) or heating of evaporities at atmosphere into volatiles the site of a large bolide impact, will 20 of evaporitic volumes Large Carribean-Columbian move vast volumes of sulphurous Generic extinctions (%) Columbia Karoo Traps and halocarbon volatiles, as well as 10 Paraná Traps River Brito-Arctic Ontong-Java solids, CO2 and CH4 into the earth's No on-site upper atmosphere (Figure 1a). The Ethiopian Traps evaporites resulting catastrophic climatic effects 0 1 2 3 4 19 20 link in time and probable causes to A. Volume of ood basalts (x 106 km3) earth-scale major extinction hori- Emeishan Traps Siberian Traps zons. (Figure 1b). In this article shall (269-265Ma) (253-250Ma) examine how three of the five major Deccan Traps CAMP, Brazil Phanerozoic extinction events have 50 3. End-Permian (67-65Ma) an evaporite association, starting with (201.5Ma) the most intense extinction event of 40 1. Late Ordovican Capitanian 5. End-Cretaceous the Phanerozoic; the end-Permian 4.Late Triassic and its link to LIP emplacement into 30 two separate sequences of massive 2. Late Devonian bedded evaporite (Cambrian or De- 20 vonian mega-salts) in the Tunguska Basin, Siberia. 10 Extinction Intensity (%) 0 End-Permian - Saline 550 500 450 400 350 300 250 200 150 100 50 interactions during em- Camb. Ord. Sil. Devonian Carb. Perm. Trias. Jur. Cret. Pal. Neo. B. Years (Ma) placement of Siberian Figure 1. End Triassic Extinction. A) Comparison of generic extinction percentages (from Sepkoski, 1996) with estimated original volumes of coevaligneous provinces, which show no correspondence Traps between the two (from Wignall 2001), until the on-site evaporite association is added (previous The Siberian Traps LIP is of signif- article), whereby all significant extinction events (>20% extinction at generic level) have an associ- icant size (~7 × 106 km2) and total ation with thermally-disturbed saline giants. Note the scale splice on the volume axis. B) Intensity of volume (~4 × 106 km3) (Ivanov et al., extinction at the genera level across geologic time (replotted from data table in Rohde and Muller, 2005). Shows the 5 main extinction events (1-5) as first defined by Raup, 1982. Extinction intensity 2013 and references therein). It is, (%) is defined as the precent of genera, from a well-resolved diversity curve which are in their last however, smaller than the Late Creta- appearance. (diversity curves were published by Sepkoski, 2002). Igneous trap emplacement times ceous Deccan Traps and has a volume are from Jones et al., 2016). that is about a half of the Late Triassic Central Atlantic Magmatic Province it seems that the volume of igneous material in a LIP does not (CAMP). All three of these continental LIPs are dwarfed by the directly relate to the intensity of the extinction event (Figure 1b). Early Cretaceous marine Ontong-Java LIP (≈20 × 106 km3). So, Page 1 www.saltworkconsultants.com 85°E 90° 95° 100° 105° 110° 96 108 120 71°N Noril'sk A. 72 B. Kotuy Putorana Maymecha Plateau Norilsk 67° Severnaya R U S S I A Nizhnyaya Tunguska Enisey Traps 64 62° Abundant magnetite pipes 1400 m 1700 m enisey Nepa Potash Y 1700 m 2000 m Basalt dyke (accessible) Angara region 57° Documented well Pipes with magnetite Ust-Ilimsk Krasnoyarsk Basalt pipes 1700 m Present-day Siberian Traps Bratsk Basalt lavas Bratsk Krasnoyarsk 56 a 1700 m r Volcaniclastic rocks Lava a g n 2000 m Doleritic intrusives 52° Volcaniclastic rocks A RUSSIA Devonian salt extent Intrusives Cambrian salt extent Thickness of Cambrian Tunguska Basin sediments Irkutsk al Irkutsk 500 km saline sediments (m) 500 km Lake Baik 2000 Lake Baikal Figure 2. Geological map of the Siberian Traps , Tunguska Basin, Russia. A) Shows present-day outcrop extent of lavas, volcaniclastics and intru- sives, along with thickness isopach of saline Cambrian carbonates and the position of the Cambrian Nepa otash region (after Black et al., 2012, 2015; Polozov et al., 2016, Zharkov, 1984). B) Shows present-day outcrop extent of lavas, volcaniclastics and intrusives, along with positions of explosive pipes with magnetite and basalt pipes as well as the approximate extent of halite dominated cambrian and devonian salt basin remnants (after Svensen et al., 2018). Maps have slightly different scales. Note the relative lack of pipes in the Nepa potash region. The Siberian Traps include ultramafic alkaline, mafic and felsic Thickness of volcaniclastic material in the Siberian Traps ranges rocks that erupted in different proportions within a vast region from intercalated layers less than a meter thick on the Putora- extending over several thousands of square kilometres across na Plateau to hundreds of meters near the base of the volcanic Western and Eastern Siberia (Figure 2a). The Siberian Traps are sections in the Angara and the Maymecha-Kotuy areas (Figure considered have been emplaced atop a hotspot in a relatively 2a). The total volume of mafic volcaniclastic material has been short time frame (≈1 million years), when a large volume of estimated at >200,000 km3 or >5% of the total volume of the deep mantle-derived igneous material was intruded and erupted Siberian Traps (Black et al., 2015). Volcanic rocks of this age at the Permo-Triassic boundary (Burgess et al., 2017). are also present in drillcore in the West Siberian Basin (Ivanov et al., 2013). Trap geology Magma-sediment and magma-water interactions active during Near Noril'sk, lava outflows reach thicknesses of over 3 km, emplacement of the Siberian Traps in the upper lithosphere en- while further to the northeast in the Maymecha-Kotuy region, compass a variety of heated evaporite interactions: batholith half of the total lava pile is composed of ultramafic rocks in- metal-evaporite interactions, lava-water interactions and intense cluding magnesian rich meimechites (Figure 2a). The very high phreatomagmatic explosions via vents and breccia pipes that MgO contents (8-40 wt %) of the meimechites in such low-de- formed saline-igneous volatile fountains reaching the upper at- gree melts indicates that the site of initial melting was very deep, mosphere. The positions of these fountains are perhaps indicated as much as 200 km, and either in the lowermost continental lith- by vent-related iron-rich diatremes (Figure 2a; Svensen et al., osphere or in the underlying asthenosphere (Arndt et al., 1995). 2009). All these interactions are critical inputs to the End-Perm- Melting probably was linked with the arrival of a mantle plume ian extinction event that links vast volumes of altered evaporites that was in its turn the source of the Siberian basaltic flood vol- with the heating mechanisms inherent to Siberian Trap geology. canism. Page 2 www.saltworkconsultants.com 10 10 10 10 10 Voisey’s Bay: Mesoproterozoic rift (anorthosite-granite-troctolite magmatism) 5 6 7 8 t Ni t Ni t Ni t Ni Raglan Kambalda Agnew, Kambalda, Raglan, Thompson: Archean rifted continental margin with komatiite lava ows 66 @ 2.9 22.1 @ 3.12 Pechenga: Paleoproterozic rifted continental margin (ferropicrite sills) Thompson Noril’sk (E) Voisey Bay 89 @ 2.5 900 @ 2.7 Great Dyke: Archean intracratonic rift hosted in Archean greenstones 124.4 @ 1.66 Agnew Jinchuan Sudbury Jinchuan: Neoproterozoic sill rifted continental margin (Rodina break-up) 10 52 @ 1.9 1 4 t Ni 515 @ 1.06 1648 @ 1.2 Merensky Reef (Bushveld): Paleoproterozoic stratiform sills (norite to anorthosite with chromitite) Mt Keith Platreef (Bushveld): Paleoproterozoic concordant sills (norite to anorthosite with chromitite) Grade (wt % Ni)Grade Flood-basalt related 478 @ 0.6 Komatiite-related Duluth: Mesoproterozoic rift (triple junction, ore within troctolitic and gabbroic igneous rocks) Basal Ni-Cu sulphides in mac-ultramac intrusions Duluth Magnesian-basalt related Sudbury: Palaeoproterozoic vein ore hosted in a norite melted by meteorite impact Astrobleme - impact-related 4000 @ 0.2 Noril’sk- Talnakh: End Permian rift (triple junction) with assimilated Devonian anhydrites 0.1 1 10 100 1000 10000 A. Production + reserves in Millions of tonnes Voisey's Bay (Basal Ni-Cu sulphides in mafic-ultramafic intrusions) 2.2 Thompson (Ni-Cu sulphides in komatiites) 3.5 Pechenga (Basal Ni-Cu sulphides in mafic-ultramafic intrusions) 4 Great Dyke (Stratabound PGEs-Ni-Cu sulphides in mafic-ultramafic intrusions) 5.4 Jinchuan (Basal Ni-Cu sulphides in mafic-ultramafic intrusions) 5.5 Merensky Reef (Stratabound PGEs-Ni-Cu sulphides in mafic-ultramafic intrusions) 6.3 Platreef (Basal Ni-Cu sulphides in stratiform mafic-ultramafic intrusions) 6.5 Duluth (Ni-Cu sulphides in intrusions related to flood basalts) 8.0 Sudbury (?astrobleme-associated Ni-Cu sulphides) 19.8 Noril'sk (Ni-Cu sulphide intrusions with evaporite assimilation and flood basalts) 23.1 0 5 10 15 20 25 30 B. Ni reserves in Millions of tonnes Figure 3. Magmatic Sulphide deposits. A) Ore grade in wt.% Ni versus production and reserves in millions of tonnes for major magmatic Ni-sulphide deposits of the world. B) Ranking of these deposits by their published reserves (after Naldrett, 1999, 2004; Warren, 2016). Evaporite basins (Devonian and Cambrian) Lake Siberian traps The Siberian Traps region is not only significant because of its A. Pyasina vast extent and its deep nickel-prone mantle source, but also (layered basalt) in that the immense volumes of igneous rocks that making up Talnakh the traps were emplaced into two chemically prone saline gi- Devonian ants with differing dominant mineralogies and ages; 1) Cam- outcrop brian mega-halite sediments in the south, with interlayers of hydrated potash salts (mostly carnallitite) and 2) Devonian Noril’sk Lake Melkoe megasulphates in the north, containing two 50-100m beds of anhydrite (Figures 2b, 5).