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Global Changes aa 2015/2016 Sergio Rocchi Dipartimento di Scienze della Terra [email protected] http://people.dst.unipi.it/rocchi/SR/Home.html registro lezioni 1 global changes •changes of what? •on which timescale? •measured how? everything changes (evolves) •early (and continuing) differentiation of the Earth •early terrestrial atmosphere and its evolution •mineral evolution vs atmosphere and biosphere early Earth •heating •age of the Earth •differentiation • mantle • core • crust • atmosphere early Earth •age of the Earth? •is the Earth older than any Earth’s material? Rogers et al. (2008) early Earth •heating and differentiation •heating causes melting that drives differentiation •heat sources • primordial collision accretion: kinetic energy E=1/2 mv2 converts to heat, with DT=mv2/[2C(m+M)] • primordial core formation: Fe-Ni “inward falling” with potential energy converted to kinetic converted to heat • radiogenic heating: primordial short-lived isotopes + long-lived U, Th, K (continental crust) • tidal heating by friction early Earth •mantle-core separation •magma ocean • melt segregation and metal-silicate equilibration Rogers et al. (2008) chemical evolution of the Earth core - mantle - crust - atmosphere • core • planetesimal accretion = energy to keep primordial Earth molten • gravitational separation of metal phases towards the core = further energy to keep the planet molten longer = more efficient segregation of siderophile elements from the mantle to the core • Fe-Ni alloy (P waves point out a lower density: ≈10% sulfide-type phases present?) • mantle • made of silicate phases (70% Earth’s mass) • underwent partial melting to generate basaltic magmas • some major elements (Na, Al, Si, Fe) preferentially enter the liquid • others (refractory elements such as Mg) preferentially stay into the solid • some trace elements (LILE) fit best into the liquid structure (more “open” than the solid) • rising mantle magmas accumulate into the crust elements with low-melting point as well as incompatible elements (including K, Th, U) 8 chemical evolution of the Earth 9 core - mantle - crust - atmosphere • crust • oceanic crust • produced by partial melting of mantle peridotite • SiO2≈50 wt% • max lifetime ≈ 200 Ma, average lifetime ≈ 60 Ma • continental crust • produced by partial melting of hydrated mantle peridotite • SiO2≈57 wt% • max lifetime ≈ 4 Ga, average lifetime ≈ 600 Ma • lower continental crust differs from upper continental crust • in the Solar system only the Eartyh has a non-basalic crust • due to the occurrence of surficial liquid water • liquid water triggeres the sedimentary process • plate tectonics (subduction of altered oceanic crust and some of the overlying sediemnts carries water also into the upper mantle) chemical evolution of the Earth core - mantle - crust - atmosphere Si Ca Fe Mg Ca Si Fe Mg Ni Na K Al lower continental crust Al Si oceanic crust Al Fe mantle Si Fe upper continental crust S (O) core 10 atmosphere and hydrosphere •composition •nitrogen and the inert gases •loss of the earliest atmosphere •water atmosphere and hydrosphere •composition atmosphere and hydrosphere •composition atmosphere and hydrosphere •atmosphere and hydrosphere produced by outgassing from volcanic activity •volcanic volatiles • major: H2O, CO2, SO2 • minor: N, halogens, hydrides • water soluble dissolve in the oceans • less-reactive, less-soluble (N, inert gases) accumulate in atmosphere •O not from volcanoes • first Ga: water breakdown by UV radiation • Archean (3.8-2.5 Ga): cyanobacteria Press et al. (2006) atmosphere and hydrosphere •a planet retain a gas with molecule velocity < 1/6 escape velocity Vesc=(2GM/r)1/2 average molecular volocity •giant planets retain any of the gases •Moon retains no gas Rogers et al. (2008) atmosphere and hydrosphere •nitrogen and the inert gases (Ar, Ne, Kr, Xe) •N inert in inorganic chemistry •80-85% was outgassed during the first few tens of Ma after accretion atmosphere and hydrosphere •loss of the earliest atmosphere •99% early atmosphere lost within 100 Ma •how? • major impact with Theia • Moon formation? atmosphere and hydrosphere •origin of water • cometary impacts • D/H in comets twice D/H in hydrosphere • outgassing of water-bearing minerals • early surface was hot, but early atmosphere was very dense earliest land •3.9 Ga • komatiites • very high mantle T or • high mantle T, water in the mantle by subduction • quartz pebbles • erosion, water (0-100°C) Rogers et al. (2008) •4.4 Ga • relic zircons 50 mm 50 mm early Earth •summary Rogers et al. (2008) evolution of the atmosphere •evolution of gas concentration evolution of the atmosphere •the atmosphere before the life •the atmosphere today evolution of the atmosphere • evolution of atmospheric oxygen concentration • Earth’s O2 from photosynthesis Great Oxidation Event (GOE) vs Great Oxygen Transition (GOT) evolution of the atmosphere the rise of oxygen Archean • • • • Proterozoic Phanerozoic non-mass-dependent (NMD) fractionation of S isotopes generated by photosynthetic reactions signal preserved in rock record if atmospheric O < 0.001% PAL trace metals enrichment in marine sediments before GOE: on-land oxidative weathering of pyrite? Present Atmospheric Level Lyons et al. (2014) evolution of the atmosphere rise of oxygen and glaciations •oxygen •biosphere •ice • rise of O • oxidize CH4 (greenhouse gas) • T drops (Ga) Snowball Earth: Makganyene Sturtian Marinoan http://www.snowballearth.org/index.html mineral evolution Hazen et al. (2010) mineral evolution Hazen et al. (2008) mineral evolution Hazen et al. (2008) mineral evolution Hazen et al. (2008) mineral evolution Hazen et al. (2008) planetary accretion (>4.55 Ga) stage 1 •> 4.56 Ga •primary chondrite minerals •chondritic meteorites: ~ 60 minerals •refractory minerals • forsterite • piroxene • troilite • Fe-Ni metals • corunndum planetary accretion (>4.55 Ga) stage 2 •4.56 - 4.55 Ga •differenziazione dei planetesimi •alterazione acquosa, metamorfismo •fillosilicati, idrossidi, carbonati crust and mantle reworking (4.55-2.5 Ga) stage 3 •4.55 - 4.0 Ga •beginning of igneous magma/ rock evolution •large mafic-ultramafic igneous bodies •cumulates • foundering: chromitites • floating: anorthosite •detrital zircons 4.4-4.0 Ga •~ 500 minerals crust and mantle reworking (4.55-2.5 Ga) stage 4 •~4.0 - 3.5 Ga •granitoid production • inizio formazione cratoni: litosfera leggera ➾ preservabile • trasporto elementi radioattivi verso la crosta superiore ➾ irrigidimento profilo litosferico • pegmatiti •~ 1000 minerals • quarzo, feldspati, anfiboli, miche • minerali delle pegmatiti (Li, Cs, B, Be, Nb-Ta) crust and mantle reworking (4.55-2.5 Ga) stage 5 •>>3.0 Ga •plate tectonics • massive sulfide deposits • exhumation of deep-seated metamorphic rocks (highPressure minerals) •large-scale hydrothermal crustal reworking •~ 1500 minerals crust and mantle reworking (4.55-2.5 Ga) stage 6 •3.9 - 2.5 Ga •Archean anoxic biosphere •~ 1500 minerals •first banded iron formations biologically mediated mineralogy (2.5 Ga-Present) stage 7 •2.5 - 1.9 Ga •Paleoproterozoic Great Oxidation Event (GOE) • fotosintesi dei cianobatteri •> 4000 minerali •~ 4300 minerali oggi noti: oltre metà rappresentano prodotti di alterazione, ossidati e idrati, di altri minerali •pur non essendo biominerali s.s., i minerali ossidati/ idrati testimoniano il contributo inderetto dell’attività biologica alla evoluzione/diversificazione dei minerali Neoproterozoic •banded iron formations •Algoma-type •Superior-type • deposition on shelves and intraplate basins of stable plates •Rapitan-type Robb (2005) Neoproterozoic Neoproterozoic •banded iron formations •contributo di microorganirmi • Fe2+, Mn2+: bio-ossidazione >> foto-ossidazione Robb (2005) early-mid Proterozoic •U (+Au) • pyrite placers (late Archean) • unique metallogenic event pre-oxygenation • unconformity-associated U (1800-1200 Ma) • hexavalent U in solution Evans (1997) biologically mediated mineralogy (2.5 Ga-Present) stage 8 •1.9 - 1.0 Ga •l’oceano intermedio •> 4000 minerali biologically mediated mineralogy (2.5 Ga-Present) stage 9 •1.0 - 0.542 Ga •“snowball Earth” •eventi di ossigenazione del Neoproterozoico •O atmosferico: 2% ➾ 15% valore attuale •> 4000 minerali •alterazione bioassistita dei feldspati: “clay mineral factory” (Ga) biologically mediated mineralogy (2.5 Ga-Present) stage 10 •< 0.542 Ga •la biomineralizzazione del Fanerozoico •> 4300 minerali •biomineralizzazione • carbonato di calcio: coralli, molluschi... • fosfati: scheletro vertebrati e invertebrati, precipitazione microbica fosforiti • ossidazione pirite (drenaggi acidi) evolution, variations, climate •registrazione variazioni nel passato •previsione evoluzione futuro •ambienti futuri già visti nel passato •archivi paleoambientali/climatici nei sedimenti near offshore •glaciovulcanismo & datazioni: strumento per ricostruzioni paleoambientali CO2 : cause, effect,proxy • CO2 - (Mauna Loa observatory) • CO2 - (molti osservatori) • Variazione stagionale, oscillazioni più pronunciate nell’emisfero Nord • cause: season photosynthesis • globale change: comparable increase in both hemispheres • T increases parallel to CO2 increase: which started first? • cause: T increase ➠ CO2 increase (photosynthetic vs anthropogenic) CO2 increase ➠ aumento T increase • seasonal variation (7 ppm = 2%) • cause: season photosynthesis • globale change: increase • cause: increasing burning of fossil fuels(greenhouse effect)? northern hemisphere winter: min photosynthesis D E E F northern hemisphere summer: max photosynthesis Rogers (2008) CK A B proxies and tools •direct measurement of T proxies • fossil atmosphere in ice cores •indirect measurement of T proxies • fossil shells in marine sediment cores • CO2 proxies and models •d18O •dD O isotope fractionation snow 18O-poor condensation (rain) 18O-enriched evaporation 16O-enriched T decrease = 18O increase fossils and seawater d18O ocean ice cap size ice cap high latitude sensitive labs Antarctica and Greenland ice cores IPCC (2007b) warm interglacial warm interglacial warm interglacial air trapped in EPICA ice cores benthic faunas more ice less ice NO2 CH4 CO2 warm interglacial atmospheric concentrations in 2000 warm interglacial proxies for recent climate variations paleoclimate variations •T proxies • d18O •CO2 proxies IPCC (2007b) paleoclimate variations •T proxies • d18O •CO2 proxies IPCC (2007b) Zachos et al (2001) past vs future high latitude sensitive labs Antarctica marine proximal sediment cores paleoclimate •nearoffshore drilling paleoclimate •methods •results near-offshore drillings •Cape Roberts •Andrill: www.andrill.org near-offshore drillings the sites Di Vincenzo et al. (2009) near-offshore drillings the age model •paleontology • diatoms • foraminifera •geochronology •magnetostratigraphy •sedimentary cycles •Sr-isotope curves near-offshore drillings provenance studies •basement clasts near-offshore drillings provenance studies •basement clasts Sandroni et al. (2011) near-offshore drillings provenance studies early-middle Miocene Sandroni et al. (2011) near-offshore drillings provenance studies •volcanic material • lava clasts • tephra Di Roberto et al. (2012) summary il clima oggi e ieri •interesse per il clima •contributo geologia • retrospettiva • the past is the key to the present (and future) •Antartide • perforazioni ghiaccio fino a 740 ka • glacio-geomorfologia • exposure dating • clima vs cronologia più antichi? rocce formatesi durante periodi glaciali e interglaciali Cenozoici Cenozoico: clima vs cronologia •sedimenti • solo in mare • perforazioni off-shore •rocce vulcaniche • Antarctic Peninsula • Marie Byrd Land • Victoria Land • Erebus volcanic province • Melbourne volcanic province • Hallett volcanic province eruzione subglaciale •Gjálp (Vatnajökull) - 1 ottobre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ eruzione subglaciale •Gjálp (Vatnajökull) - 1 ottobre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ eruzione subglaciale •Gjálp (Vatnajökull) - 1 ottobre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ eruzione subglaciale •Gjálp (Vatnajökull) 2 ottobre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ eruzione subglaciale •Gjálp (Vatnajökull) - 3 ottobre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ eruzione subglaciale •Gjálp (Vatnajökull) - 3 ottobre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ National Geographic, May 1997 National Geographic, May 1997 Gjálp (Vatnajökull) - 5 novembre 1996 •Gjálp (Vatnajökull) - 5 novembre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ •Gjálp (Vatnajökull) - 5 novembre 1996 photo by M-T. Gudmusson, http://www.hi.is/~mmh/gos/ glaciovolcanic sequences paleoenvironmental tool •c’era un ghiacciaio? •spessore del ghiacciaio •quota max del ghiacciaio •struttura del ghiacciaio • neve/firn • ghiaccio integro/fratturato (permeabile) •regime termico del ghiacciaio • temperato vs polare • età del ghiacciaio (dataz. isotopica) volcano-ice interactions •RATIONALE • ice thickness/type affect eruption style • eruption style indicates ice thickness/type •PALEOENVIRONMENT • sequences of glaciovolcanic lithofacies are key indicators for past ice thickness, extent, type, and age • recognition of different types of volcanic lithofacies is essential for environmental interpretations •DIFFICULTIES • rapidly evolving morphology of the volcanic edifices subglacial eruptions - factors •temperatura del ghiaccio • energia necessaria per fondere ghiaccio • maggiore energia per fondere ghiaccio polare • la stessa quantità di magma fonde una quantità di ghiaccio polare minore rispetto a ghiaccio temperato •reologia del ghiaccio • ghiaccio più freddo è più rigido • ghiaccio sporco è più rigido •idrologia del ghiaccio • ghiaccio temperato ha acqua alla base • ghiaccio polare è solido fino alla base • acqua di fusione polare non può sfuggire dalla base thin ice Smellie (2001) thick ice, thin permeable layer Smellie (2001) thick ice, thick permeable layer Smellie (2001) Gemelli (2009) subaerial lavas subaqueous hyaloclastites lava-fed deltas •lava enters water (marine, lacustrine, glacial) •fossil water/ice levels lava-fed deltas in englacial lakes •Antarctica, northern Victoria Land •late Miocene-Quaternary volcanic sequences •volcanic lithofacies generated in association with a Neogene ice cover lava-fed deltas • forms when lava enters (glacial) water • indicators of fossil water (and ice) levels •pahoehoe vs. aa lava-fed deltas Smellie et al. (2013) aa lava-fed delta •subaerially emplaced relatively thin caprock of aa lavas lying on and passing down-dip to •very crudely developed subaerial to subaqueous transition (passage zone) •distinctive chaotic subaqueous association of abundant lava lobes and hyaloclastite with admixed vesicular, often reddened (oxidized) lava clinkers •rare subaqueous stratification with predominantly low dips and layer thickening •glaciovolcanic lava-fed delta advancing through cold-based ice •only supraglacial meltwater discharge •dome or coulée advancing in wet-based ice •subglacial meltwater escape •basal tills and eruptionrelated fluvial sandstones and conglomerates Smellie et al. (2011) paleoenvironment-paleoclimate Smellie et al. (2011) •warm- to cold-based glacier transition in Antarctica no erosion ice sheet pulsations warm-based glaciers Zachos et al. (2001) fast exhumation river incision paleoenvironment-paleoclimate • basal thermal regime • determines the potential ice sheet instability • 30-years paradigm for EAIS (VL) • basal thermal regime: from wet-based to coldbased either at ca. 14 Ma or after ca. 2.5 Ma • paleo-ice thicknesses/regime from subglacial eruptions along 800 km of the Ross Sea coast • evidence for both wet- and cold-based ice • basal thermal regime varied spatially and with time between ca. 12 Ma and present: it was polythermal • coarse temperature patchwork of frozen-bed and thawed-bed ice, similar to the EAIS E today • paradigm shift Smellie et al. (2014) global climatic changes - greenhouse greenhouse gases - origin gases •GHG affects climate •origin of GHG • anthropic activities • volcanic activity • subvolcanic activity? atmospheric effects of volcanic eruptions •volcanoes release SO2 •SO2 reacts to H2SO4 = aerosol •generally Sa > La = aerosol layer induces cooling gas and dust from LIP volcanoes •Large Igneous Volcanic Provinces climate effects of volcanic LIPs aerosol Rogers (2008) biological effects of volcanic LIPs •... and their subvolcanic counterparts? Wignall (2001) Subvolcanic LIPs (Large Igneous subvolcanic LIPs Provinces) North Atlantic 55 Ma Paleocene-Eocene Siberia 250 Ma Karoo 183 Ma Toarcian subvolcanic structure of LIPs Hansen & Cartwright (2006) Rocchi et al (2007) subvolcanic structure of LIPs •saucer-shaped sills •forced folding Rocchi et al (2007) 24 subvolcanic structure of LIPs Polteau et al (2008) subvolcanic structure of LIPs Golden Valley, Karoo, South Africa 10 km subvolcanic structure of LIPs •hydrothermal venting Svensen et al. (2004) Rocchi et al (2007) sediment fluidisation & venting •emplacement of magma in wet sediments •critical pressure of water •Senegal: shallow emplacement depth • ≈ 1 s TWT ≈ 350 m • P ≈ 7 MPa < critical pressure of water • explosive expansion of water • fracture-induced P reduction 1.25 1.5 2 4 6 1 Pressure (MPa) • 22.1 MPa for pure water ≈ 1.1 km of wet seds • 31.2 MPa for seawater ≈ 1.6 km of wet seds Kokelaar (1982) 40 8 10 30 12.5 15 20 Liquid 20 25 33 10 50 Vapour 0 •heat source = persistent vapour •high vapour flow rate = sediment fluidization •continuous vapour flow = sediment transport 0 200 400 Temperature (°C) 100 600 sediment fluidisation & venting modified after Jamtveit et al. (2004) venting to the seafloor crater, diatreme venting to the seafloor mud volcano igneous dyke further fluids rising pipes of finer grained sediments hydraulic brecciation of sediments, fluids escape to the surface peperite + sediment fluidization sill intrusion in wet sediments GHC from subvolcanic intrusions •contact aureole around a sill intrusion emplaced into sedimentary rocks •overpressure in the aureole may cause venting of fluids to the atmosphere •fluids are ALSO produced in contact aurole by • kerogen cracking to methane • hydrous minerals releasing H2O • TOC content decreases towards the contact • vitrinite reflectance increases towards the contact Aarnes et al. (2010) GHC from subvolcanic intrusions H2O (sandstone, clays) • CH4 (shale, petroleum) • CO2 (coal, lime/ dolostone) • CH3Cl (evaporite) • SO2 (evaporite) • HCl (evaporite) Svensen & Jamtveit (2010) • global warming from subvolcanic GHG? •important global warming episodes • 55 Ma, Paleocene-Eocene • 183 Ma, Toarcian (early Jurassic) • 250 Ma, end-Permian North Atlantic 55 Ma Siberia 250 Ma Karoo 183 Ma Subvolcanic LIPs (Large Igneous Provinces) North Atlantic 55 Ma Paleocene-Eocene Siberia 250 Ma Karoo 183 Ma Toarcian GHC from North Atlantic PETM LIP •rapid (20-200 ka) global warming around 55 Ma •global T rising of about 6°C (0.03°C/ century) Zachos et al (2001) •negative excursion in carbon stable 13 isotope (δ C) massive input of •massive 13 C-depleted C in the hydrosphereatmosphere C for PETM •C source that caused the global climate change: extensive melting of gas hydrates buried in marine sediments? •large-scale hydrate melting requires a triggering mechanism •thousands of hydrothermal vent complexes of Paleocene-Eocene age identified on seismic reflection profiles from the Norwegian Sea •intrusion of voluminous magmas in Crich sedimentary strata caused explosive release of CH4 •CH4 was transported to the ocean or atmosphere through vent complexes Svensen at al. (2004) C for PETM •magma volume: 104-105 km3 •age: Paleocene-Eocene boundary •host rocks: organicrich Cretaceous and Palaeocene mudstones Svensen et al. (2004) C for PETM •host rocks: organic-rich Cretaceous and Palaeocene mudstones 18 •release of 0.3-3 x 10 g CH4 •thermogenic CH4 from organic material has low C isotope ratio 13 (d C = -35 to -50‰) Svensen et al. (2004) Aarnes et al. (2010) C for PETM •volcanic vs subvolcanic GHG •direct C emissions • 1 m3 magma emits 3.6 kg C • volcanism 10x more voluminous than intrusions • C from volcanism 10x C from intrusions •indirect C emissions (net flux into the atmosphere) • 1 m3 magma intruded in organic C-rich mudstone emits 25-100 kg C • C from intrusion > C from volcanism Toarcian - Karoo Toarcian - Karoo •thermogenic CH4 from organic material has low C isotope ratio (d ( 13C = -35 to -50‰) owing to preferential incorporation of 12C during photosynthesis Svensen et al. (2007) Siberia - end-Permian Svensen et al. (2009) Siberia - end-Permian Svensen et al. (2009) Siberia - end-Permian Svensen et al. (2009) global climatic changes - greenhouse greenhouse gases - origin gases •GHG affects climate •origin of GHG • anthropic activities • volcanic activity • subvolcanic activity!
