IODP Workshop Proposal Large Igneous Provinces

Executive Summary

We propose an IODP workshop to define the key scientific objectives of investigating transient large igneous provinces (LIPs), to identify a global, long-term drilling strategy and the technological requirements for addressing the scientific objectives, and to provide a conceptual framework for potential consideration of this Earth, Oceans, and Life initiative as a dedicated IODP mission.

Overall Scientific Objectives

Transient large igneous provinces (LIPs), encompassing oceanic plateaus, magma- dominated ‘volcanic’ divergent margins, submarine ridges, and ocean basin flood basalts in the oceans, and continental flood basalts on land, constitute a first-order problem in Earth science. Their origin does not conform to standard plate tectonic theory, so the processes involved in their formation are critically important for understanding mantle and crustal geodynamics, and investigating relationships between their emplacements and major environmental changes is crucial for advancing our understanding of the Earth system. Earth, Oceans, and Life highlights LIPs as a high-priority initiative for IODP, and the major goal of our proposed LIP workshop is to develop strategies for achieving a better understanding through scientific ocean drilling of both solid Earth processes and changes in Earth’s environment associated with LIP emplacement. The proposed workshop will be the first comprehensive examination of the role of ocean drilling in understanding of LIPs since the JOI/USSAC workshop ‘Large Igneous Provinces’ in 1990. Since that time, we have witnessed exciting advances in LIP-related solid Earth and Earth system studies, as well as major improvements in drilling, logging, borehole monitoring, and site surveying technologies applicable to LIP investigations. Furthermore, five active IODP proposals (#s 623, 630, 654, 658, and 706) target transient LIPs, making this workshop timely for developing a global, long-term drilling strategy for these enigmatic features.

In comparison to the terrestrial planets and moons, plate tectonics may well be unique to Earth. Even on Earth, current plate tectonic theory does not predict major crustal growth events, of which LIPs are an excellent example. They represent exceedingly large (>105 km3) emplacements of predominantly mafic magmas that are difficult to explain by conventional plate boundary magmatism. The largest occur in the ocean basins, where they include giant plateaus such as Ontong Java in the western Pacific and Kerguelen in the southern Indian Ocean. Similarly, flood basalts were erupted along many ‘volcanic’ passive margins (e.g., Greenland, Norway, Brazil, Namibia, NW Australia) during continental breakup, as well as in continental settings (e.g., Columbia River in the U.S. Pacific Northwest, Deccan in India, Parana in Brazil, Karoo in southern Africa, and Siberia in Asia). Primarily because of ease of access, continental flood basalts are the best sampled and dated type of LIP. Recent improvements in geochronology have demonstrated that all well-dated continental flood basalts provinces initially thought to have formed over many tens of millions of years, instead formed in a few million years or less, with the exception of Kerguelen. The rapid melt production rates documented by the eruption of huge volumes of magma in such short time intervals implies a generation mechanism other than rifting, since passive rifting alone cannot produce such high melting rates. This realization has led to other models involving: the melting of a plume of deep, hot, mantle that rises to the surface from the core-mantle

Large Igneous Provinces Workshop, Coffin & Neal 1 9 August 2006 boundary; upflow of deep (more fertile) upper mantle in areas where plate thickness varies greatly; and bolide-induced decompression melting of the upper mantle. Again, standard plate tectonic theory does not predict the massive magmatism resulting in LIP formation.

Drilling, coring, and logging of the / (KP/BR) system (ODP Legs 119, 120, and 183) and the (OJP: Legs 130 and 192) led to the discovery that LIPs can have quite different origins. The origin of neither LIP is adequately explained by melting of a large single plume head. Much of the KP/BR LIP is capped by lava that erupted subaerially between 119 and 89 Ma. The Ninetyeast Ridge (ODP Leg 121) marks the subsequent track of the Kerguelen hotspot from 83 to 38 Ma. However, geochronology of the uppermost igneous crust suggests that the plateau formed over a prolonged period (119-68 Ma). In contrast, the uppermost igneous crust of the OJP formed entirely in a submarine environment and consists of compositionally similar basalt erupted at ~122 with relatively minor contributions at ~90 Ma. Uplift associated with emplacement and subsequent subsidence are both anomalously minor, and an associated trailing hotspot track is absent. Consequently, non-plume alternatives have been proposed, such as a bolide impact and plate tectonic processes, and need to be tested. In contrast, drilling, coring, and logging of the Norwegian (Leg 104) and SE Greenland (Legs 152 and 163) volcanic divergent margins has provided strong evidence for a mantle plume impacting the lithosphere and later continental rupture. Drill holes in these areas, including the two deepest, by ODP or any submarine LIP standards, sites— Site 642 on the Norwegian margin penetrated 914 m of igneous basement, and Site 917 on the SE Greenland margin 833 m— together with shallower penetration basement holes, document subaerial eruption environments, decreasing continental influence in the basalts during continental breakup, and focusing of plume activity towards the Greenland-Scotland Ridge during early seafloor spreading. Temporal correlations between LIP emplacements, including those above, and environmental changes such as oceanic anoxic events, speciations, extinctions, biocalcification, variations in oceanic C and Sr isotope ratios, and variations in oceanic metal concentrations are relatively well known, yet causal mechanisms for the changes remain the subject of lively debate (e.g., 2003 Plume IV – Beyond the Plume Hypothesis Penrose Conference; 2005 The Great Plume Debate Chapman Conference; 2005 GSA Special Paper 388 Plates, Plumes, and Paradigms; www.largeigneousprovinces.org; www.mantleplumes.org). Determining how solid Earth processes are linked to changes in the Earth’s environment is crucial for understanding the Earth system.

The full consequences of LIP formation have only recently begun to be appreciated. The following connections between LIPs and Earth evolution, which this workshop will focus on, need to be examined:

• implications for mantle convection and heat loss from the Earth’s interior; • interaction of LIP events and the plate tectonic cycle; • possible connections between LIP events and changes in the reversal frequency of Earth’s magnetic field; • compositions of magma as ‘windows’ into the deep mantle; • possible role as dominant non-plate-tectonic heat-loss mechanism of all terrestrial planets; • role in continental growth; • physical volcanology that modulates particulate and aerosol release into the oceans and atmosphere, and governs the eruption of basaltic flows covering many thousands of km2;

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• volatile concentration of LIP magmas and the volatile load delivered to the oceans and atmosphere; • potential consequences of LIP eruptions for oceanic and atmospheric chemistry; • possible connections between LIP events and acceleration/retardation of the evolution of life on Earth.

Specifically, in light of currently active LIP-related IODP drilling proposals, workshop participants will:

• identify and describe the possible consequences of LIP activity for the evolution of the solid Earth, its oceans, atmosphere, and biosphere; • suggest routes of inquiry that will most effectively advance understanding of the causes and consequences of LIP events; • design a strategy for construction of a long-term science plan, incorporating technological, engineering, and operational advice, for research on LIPs.

Strategies must combine observation, sampling, remote and in situ data acquisition, and quantitative modeling to encompass: deep earth structure and geodynamics; magma formation and magma evolution; volcanic and tectonic construction at LIPs; deep fluid circulation and fluid-rock interaction; fluid behavior and chemical interactions at and near the seafloor; and paleoenvironmental responses and feedbacks. Strategies must also be developed for understanding the microbial ecosystems that may exist where fluids flow within LIP crust. Microorganisms may mediate chemical budgets by catalyzing and deriving energy from a wide variety of geochemical reactions.

Rationale for Drilling

Scientific ocean drilling has played a pivotal role in advancing our knowledge of LIPs. Nevertheless, the tremendous opportunities offered by the new riser vessel Chikyu, the more capable riserless scientific ocean drilling vessel, and mission specific platforms are not thoroughly understood nor have they been widely discussed in the scientific community. The prospect of deeper basement penetrations of LIPs, of shallow water drilling, and of improved recovery of alternating hard (e.g., chert) and soft (e.g., chalk) lithologies has excited individual and small groups of researchers, but has not been considered by a broad, multidisciplinary group of scientists formulating coherent strategies to advance LIP research. The proposed workshop will provide a forum for educating the community about new drilling, logging, and borehole monitoring capabilities, as well as new site surveying capabilities (e.g., R/V Langseth and commercial 3D seismic), and foster discussion of the optimal ways and targets to utilize them on the frontiers of our science.

Developing new approaches and strategies for drilling, and combinations thereof, to address the outstanding scientific problems posed by LIPs will be a major goal of the workshop. New or enhanced lines of inquiry to be considered will include:

• composite section construction utilizing tectonic exposures, e.g., rifted Manihiki and Hikurangi Plateau flanks combined with in situ sections, obducted Ontong Java and Caribbean sections combined with in situ sections; • conjugate onshore-offshore transects of continental flood basalts/divergent volcanic margins, e.g., Parana-Etendeka, Deccan-Seychelles, Eastern North America-

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Northwest Africa (Central Atlantic Magmatic Province), East Antarctica-Kerguelen, Karoo-Ferrar, East Greenland-United Kingdom; • syn-sedimentary sections, from both above and below the carbonate compensation depth (CCD), that preserve the volcanic histories of all types of individual oceanic LIPs as well as potential environmental impacts; • feather edge sections preserving condensed sections of all types of individual oceanic LIPs; • thick sections that preserve the histories of peak magmatic flux and geochemical variability for all types of individual oceanic LIPs; • shallow water (especially atolls) and Arctic drilling to recover LIP sections, not possible prior to the IODP; • core-log-seismic integration to relate LIP drilling to geophysical data from LIPs.

Specific scientific problems addressable by drilling, coring, and logging of LIPs, utilizing the technologies and strategies outlined above, include:

• mantle source, plume or otherwise, behavior, from volcanic flux and petrological/geochemical variations through time, and uplift/subsidence histories; • testing of plume, bolide, and plate tectonic models for LIP emplacement, using geochronology, petrology, geochemistry, and vertical tectonic history; • temporal relationships between LIPs and continental breakup, from geochronology of LIP rocks; • environmental—physical, chemical, biotic—changes either contemporaneous with, leading, or lagging an individual LIP emplacement, from syn-sedimentary sections; • testing of thermal models for LIP mantle roots, from borehole heat flow determinations coupled with seismic observations; • evaluation of physical volcanological models for LIP construction, from core-log- seismic integration.

Target Audience

To date, no meeting, committee, or panel has brought together scientists from the entire spectrum of disciplines concerned with the study of LIPs—geochronology, marine geophysics, petrology, geochemistry, mineral physics, rock deformation, oceanic and atmospheric chemistry, physical volcanology, paleomagnetics, tectonics, seismology (including tomography), geodynamics, micropaleontology, paleoclimatology, paleoceanography, paleoenvironmental modeling, sedimentology, remote sensing, and planetary geology. A major objective of the proposed workshop is to define an integrated and interdisciplinary approach to addressing the outstanding scientific problems and to devise potential solutions via drilling. Proponents of LIP-related IODP drilling proposals will be solicited to participate, as will International Union of Geodesy and Geophysics (IUGG) International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Commission on Large Igneous Provinces (www.largeigneousprovinces.org) and www.mantleplumes.org mailing list recipients.

Deliverables

Deliverables include an Eos meeting report, a Scientific Drilling white paper on LIPs, and a comprehensive workshop report describing scientific objectives, presenting drilling strategies for addressing those objectives, and identifying technological and engineering

Large Igneous Provinces Workshop, Coffin & Neal 4 9 August 2006 requirements. If, by the time of this workshop, proponent guidelines for mission proposals are available, a mission proposal for LIPs will likely be forthcoming. In addition, this workshop will lead to special LIPs/IODP sessions at American Geophysical Union (AGU), Japan Geoscience Union (JPGU), Asia Oceania Geosciences Society (AOGS), European Geosciences Union (EGU), and other international meetings that will reach the broader community.

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