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Life & Tectonics -Nicholas W. Hayman Tanya Atwater visualization of subduction and seafloor spreading: http://emvc.geol.ucsb.edu/2_infopgs/IP1GTect/eSoAtlantic_CutGlobe.html 1. Rationales for considering Earth’s Plate Tectonics seriously in the context of Origin of Life & Extraterrestrial Life studies. 2. Plate Tectonics - Subduction Zones inc. glimpses into the early Earth - Mid-Ocean Ridges 3. Examples of Marine Geology & Geophysical Observations from - Pito Deep - Atlantis Massif - The Cayman Trough East Pacific Rise hydrothermal Black Smokers showed vent studied by Karen Von Damm (in memoriam) in 1994 us that life exists in the on extreme seafloor Alvin Dive 2740. environment, far from the sun’s direct energy “Snowblower” events (Haymon et al., 1993) eject particulate microbial mass from the subsurface http://www.whoi.edu/oceanus/feature/the-remarkable-diversity-of-seafloor-vents The seafloor & subseafloor environment in general is teaming with microbial life Pacific Basaltic Lavas Number of Sequences # Operational Taxonomic Unit Santelli et al. (Nature, 2008): Microbial diversity is greatest in basaltic lavas & moderate temperature vents Metals, sulfides, acidic conditions (H+), Mg-silicates (buffers seawater), high thermal gradients, high flux The pits of Cyprus powered the Copper Age! Drilled mantle lithologies ODP Legs 149, 173 and 210 Along a transect off Iberia (Spain & Portugal) & Newfoundland Site 1277 Site 1070 Site 897C Site 1068 Newfoundland Iberia Péron-Pinvidic and Manatschal (2009) + Serpentinization can (does not have to) produce H , CH4, and sequester CO2 (into carbonates) in lower-T systems Fayalite + water → magnetite + aqueous silica + hydrogen 3Fe2SiO4 + 2H2O → 2Fe3O4 + 3SiO2 + 2H2 Forsterite + aqueous silica → serpentine 3Mg2SiO4 + SiO2 + 4H2O → 2Mg3Si2O5(OH)4 Forsterite + water → serpentine + brucite 2Mg2SiO4 + 3H2O → Mg3Si2O5(OH)4 + Mg(OH)2 Olivine + water + carbonic acid → serpentine + magnetite + methane (Fe,Mg)2SiO4 + n·H2O + CO2 → Mg3Si2O5(OH)4 + Fe3O4 + CH4 Olivine + water + carbonic acid → serpentine + magnetite + magnesite + silica (Fe,Mg)2SiO4 + n·H2O + CO2 → Mg3Si2O5(OH)4 + Fe3O4 + MgCO3 + SiO2 Most work on Ocean Worlds suggest serpentinization of seafloor was (is?) significant (e.g. Vance, 2007) Enceledus Jets from Nasa.gov Could there be other planetary systems of interest (e.g. Mars ”Chaos” from clathrate dissolution & collapse?). - Courtesy of Joe Levy Sylvan et al., 2017 A place like Lo’ihi seamount (off Hawaii) is a current favorite astrobiology analog: intraplate deep-mantle-sourced volcanism with layers of bacterial mounds. Perhaps some planetary bodies can have similar volcanism driven by tidal forces. 1. Rationales for considering Earth’s Plate Tectonics seriously in the context of Origin of Life & Extraterrestrial Life studies. 2. Plate Tectonics - Subduction Zones inc. glimpses into the early Earth - Mid-Ocean Ridges 3. Examples of Marine Geology & Geophysical Observations from - Pito Deep - Atlantis Massif - The Cayman Trough From NOAA Ocean Exploration Some contain serpeninization products, hadal zone (> 6-km water depths) conditions, and pervasive low-temperature fluid flow From Fyer et al., IODP materials Subduction-zone trenches are sediment dominated, though they do exhibit low-T seeps & active fluid flow. BUT microbially not very diverse nor high biomass. MAFIC (Magnesium, Iron, Silica, Sodium): FELSIC (Iron, Silica, Aluminum, Potassium): Basalt, Gabbro Granite, Andesite Subduction Zone Factory: H2O, C, non-lithophile Elements, … go into deeper mantle Pan African (~870-550 Ma) mountain belts were very hot (thermal gradients higher than today’s mountains), and mark the great phase of major arc accretion in some analyses What was the history of Plate Tectonics? Multicellular life Core drop, Moon formation, 26Al decay End of (not all at same time) Banded Iron heavy Oldest zircons Formations: bombard (continental crust?) Ocean ment Oxygenation 1. Rationales for considering Earth’s Plate Tectonics seriously in the context of Origin of Life & Extraterrestrial Life studies. 2. Plate Tectonics - Subduction Zones inc. glimpses into the early Earth - Mid-Ocean Ridges 3. Examples of Marine Geology & Geophysical Observations from - Pito Deep - Atlantis Massif - The Cayman Trough Clive Lister (early 1970’s) recognized that the diffused heat from a mid- ocean ridge is lower than predicted Rare case of prediction. 1979 identification of black smoker hydrothermal vents on Galapagos spreading center http://www.oceannetworks.ca/introduction- endeavour-0 Note most heat-flow is on axial flanks and off axis, and dynamic environment exists in the “Deep Crustal Aquifer” From Fisher website (UCSC) Alt et al., 1996 Discharge >0°C Recharge (~350°C) IODP Results in same time frame (Hole 504B) = high- grade metamorphic rocks near AMC w/ step-wise drop Lavas in assemblage to lower- greenschist/very-low- Reaction Zone metamorphic (metasomatic) Dikes grade upward into lavas. Broad recharge & discharge driven by “reaction zone”. Magma Chamber1100°C From Hasenclever et al. (Nature, 2014): Based on seismic velocity modeling (e.g., Dunn et al., 2000) steep gradients & axial flow continue to be model benchmark. Localization of flow only in pipe- flow at top. 1. Rationales for considering Earth’s Plate Tectonics seriously in the context of Origin of Life & Extraterrestrial Life studies. 2. Plate Tectonics - Subduction Zones inc. glimpses into the early Earth - Mid-Ocean Ridges 3. Examples of Marine Geology & Geophysical Observations from - Pito Deep - Atlantis Massif - The Cayman Trough 1.Fast-spreading EPR faulting & hydrothermal flow - Basalt flows bury the near-axis fault system - In submarine exposures & geophysical images = network of fractures & localized faults with geochemical (mineralogical) variations (across scales) 2.Detachment faulting & slower spreading centers - Impressive signatures of faulting sculpt the seafloor - Seafloor observations of serpentinized mantle contrast w/drill- hole & geophysical images of distributed fracturing and broad geochemical (mineralogical) gradients in crystalline rocks 3. Mantle vs. Crustal Rocks still not sorted, but we’re getting there? Flows Drape the Surface From CBS News GeoMapApp EPR 9°N ~6 km 9°29’ 9°29’ Abyssal Hills ~1 km moho ~5 km Juan de Fuca Plate regional seismic image; Han et al. (JGR, 2016): Reflectors = density anomalies ~150 m wide Seafloor fault scarps do not everywhere (anywhere?) match subsurface reflectors 2005 (yikes!) Pito Deep Expedition: Inspect Rift Walls Exposing a Cross-Section of EPR-Spread Crust; Rift a bi-product of microplate rotation AH – Abyssal Hills; A, B = focus areas; PD is rift with dredged mantle rocks from base Hayman and Karson, 2009 National Deep Submergence Facility Alvin Jason II Characteristics of a fault zone: Offsets base of the lavas (but not sediment); Change in Dike orientation; Several “strands”; Veins and alteration minerals; Exposure near debris-filled reentrants Multiple increments of Heft et al. (2008): veining & cataclasis Amphibole- sulfides plagioclase: 573-747°C Barker et al. Ti-in-Quartz : ~450°C 87/86Sr-composition of Quartz-breccias requires mixing of seawater & discharging fluids (Barker et al., 2010) Additional geochemical evidence in Hayman & Karson (G3, 2009) ? Recharge & discharge mixing in fault zones Time integrated geologic record ~16,000 years of spreading (e.g. >120 mm/yr full rate) Abyssal Hills don’t form until >1-km of spreading (outside the high-T discharge environment); see Buck (2001) Off-axis faults = abundant pore space & low-T min. (e.g., corrensite) Magma-Rich, Faster Spreading, Hotter Mantle Many overlapping, but some different Magma-Poor, Slower Spreading, Colder Mantle microbe-supporting volatile-rock exchange geochemical cycles Slow-Spread Mid-Ocean Ridges (<30 mm/yr) 9 Myr Atlantis OCC Massif 0.5-2 Myr 3 Myr OCC Mid-Atlantic Ridge >2-4 km of relief on massifs (oceanic core complexes) Large gravity anomalies Complex magnetic anomalies AUV “microbathymetry” from Mid-Atlantic Ridge (Escartin et al., G3, 2017) Generation of corrugations still unclear, but probably rheology- limited (e.g. plastic deformation of footwall) Spencer et al. (GSAB, 2001): Magellon image of Artemis Corona. Corrugated Surface (scalebar = 50 km) Corrugations on Atlantis Massif (Lost City Field) exposures on transform wall = serpentinized peridotite Blackman et al., 2005 Karson et al., 2006 On top of Atlantis Massif: Lost-City Field: Peridotite hosted, low-temperature, carbonate+brucite towers. (from Ocean Exploration, NOAA) Tested hypothesis of mantle exhumation by Diabase drilling: To paraphrase Jeff Gee while sailing to the site: “I predict it’s gabbro all the way down” Harz+ Oxide Gabbros Gabbros + Ol-gabbros+ Troctolites From Castelain et al., 2014 Drilling (2005) found gabbroic (crustal) section. Still energy sources (e.g. Ti-Magnetite oxidation) Diabase Harz+ Oxide Gabbros Gabbros + Ol-gabbros+ Troctolites Because of seafloor spreading, some of the only magnetic-anomaly constraints on Caribbean-North American Plate motion (which incidentally fixes a lot of the global plate circuit) 43 Ma 1 Ma Red Arrow = Mid-Cayman Spreading Center (MCSC) James Cameron’s classic film was “set” in the Cayman Trough, but filmed in a Nuclear Missile Silo. Not the only cold- war connection… Early testing ground for Alvin; led to a 1970’s era Ballard-Fox expedition: Caytrough! (photo from Pito Deep 2005) Hayman et al. (G3, 2011): ~20-myr of Magnetic anomalies Difficult to interpret More striped & possible to interpret
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