Geology Paper

REVEAL: REmote Views and Exploration of Antarctic Lithosphere Workshop: The future of Antarctic airborne geophysical capabilities—Workshop Report Compiled by Carol A. Finn Edited by Carol Finn, Sridhar Anandakrishnan, John Goodge, Kurt Panter, Christine Siddoway, and Terry Wilson This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Open-File Report 03-065 U.S. Department of the Interior U.S. Geological Survey REVEAL: REmote Views and Exploration of Antarctic Lithosphere Workshop: The future of Antarctic airborne geophysical capabilities WORKSHOP REPORT August 5-8, 2002 Denver, CO Compiled by Carol A. Finn Edited by Sridhar Anandakrishnan, John Goodge, Kurt Panter, Christine Siddoway, and Terry Wilson "Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation." 2 EXECUTIVE SUMMARY Antarctica is a key element in Earth’s geodynamic and climatic systems, yet on the eve of the 50th anniversary of the International Geophysical Year, we lack fundamental geologic and geophysical data from the deep interior of this vast continent. Meager exposures record the 3500 million-year history of a continent that participated in the formation and breakup of both the Rodinia and Gondwana supercontinents. It continues to be tectonically active today, although its kinematic relation to the global plate circuit and its role as substrate to the world’s major ice sheets remain in question. The Mesozoic break-up of Gondwana resulted in a major re-arrangement of the continental masses, which isolated Antarctica from mid-latitude oceanic influences by establishing the powerful circum-Antarctic current. This event was largely responsible for development of the massive West and East Antarctic ice sheets that blanket 98% of the continent and fundamentally influence world climate today. The West Antarctic Ice Sheet (WAIS) contains enough grounded ice to raise global sea level 5 meters, were it to melt completely, and hosts ice streams that potentially could evacuate the ice over short geologic timescales. Recent measurements show the ice sheet is undergoing rapid and dramatic change in some regions and reveal an ice-sheet-wide history of large fluctuations in extent and volume. Although the East Antarctic ice sheet is apparently more stable, it exerts a profound influence on global climate and covers numerous subglacial lakes that may have existed for millions of years. Major interest lies in the age of these lakes, their tectonic history, their resident biota, and the record of Antarctic climatic history that may be contained in the sediments beneath them. Global geodynamics was and continues to be a major influence on the formation, nature, and dynamics of the ice sheets. In turn, understanding geodynamics requires deciphering Antarctic geologic and tectonic history. For example, the mass balance and response of the WAIS to climate 3 forcing appear to be strongly influenced by geologic and geophysical parameters such as the distribution of sedimentary basins and the geothermal heat flux into the base of the ice. Precambrian structures may have influenced the style and location of younger tectonic and magmatic events that are manifested by the major features of the continent today, such as the Paleozoic and Mesozoic orogens of the Transantarctic Mountains, Mesozoic rift zones, and Cenozoic volcanic provinces. In turn, these events have influenced ice sheet dynamics and, therefore, global climate. Despite the central role that Antarctica has played in shaping the present global environment, fundamental, first-order parameters such as bedrock elevation, lithology, structure, age, tectonic history and ice volume remain poorly known over large portions of the continent. Given the extensive ice cover, airborne geophysical data, constrained by field-based geologic mapping, ground-based geophysics, and petrologic, geochemical and geochronological analysis of outcrop and drill-hole samples, is the best way to characterize broad areas of the Antarctic lithosphere. However, the U.S. Antarctic program currently lacks an effective means to collect and integrate airborne geophysical data with other datasets under broad science objectives defined by the earth science community. Regional high-resolution aerogeophysical coverage is also required by other national Antarctic research programs. In order to address scientific and logistical issues, the National Science Foundation sponsored an international workshop attended by 45 geologists, geophysicists and glaciologists in Denver, CO in August, 2002. The REVEAL workshop framed a set of key issues in Antarctic research that require airborne gravity, magnetic, laser altimetry and ice-penetrating radar measurements from long- and mid-range fixed-wing and helicopter platforms. Science goals and potential target areas were developed in the context of three major themes: (1). geology and ice sheet dynamics; (2). crustal architecture of the East Antarctic shield, and (3). geodynamics of rifting in an ice-covered environment. Investigations directed at these themes will form the basis for an integrated, 4 multidisciplinary initiative to study the relationship between Antarctic geodynamic processes, ice sheet dynamics and global environmental change. Specific goals of these research themes are outlined here. 1. Geology and ice sheet dynamics. Antarctic geological processes are the driving forces for ice sheet dynamics and global environmental change that affect current and long-term large-magnitude sea level changes. Key scientific issues are: • What are the geologic controls on ice sheet dynamics? o Extensional tectonics form rift basins and generate high heat flow that influence basal ice conditions. Measuring the 3-d geometry of rift basins and location of sub- ice volcanoes will help clarify the relation between tectonics and ice sheet dynamics. o Paleoclimate and ice sheet modeling studies are hampered by incomplete knowledge and/or poor resolution of boundary conditions which include reconstructions of global and regional paleogeography, paleotopography, heat flow, distribution of subglacial sediments, and Cenozoic volcanic rocks. • What are the masses of the ice sheets and fluxuations of sea levels on different time scales? o In order to understand the relation between ice mass balance and sea level, the current volume of the ice sheet needs to be determined. • What are the distribution, nature and origin of the sub-glacial lakes and their relation to crustal structure and heat flow? o The presence of subglacial lakes may have important implications for ice sheet dynamics as well as for terrestrial and marine glacial environments. Study of the lakes provides a means to understand the interaction between geologic and biologic processes. In addition, the extreme environments of these lakes may be analogous to those of early Earth and planets, revealing the conditions under which life began. 2. Crustal architecture of the East Antarctic shield. Unraveling the role of Antarctica in global geodynamic processes requires a basic understanding of the poorly-known East Antarctic shield and West Antarctic basement. Key questions to be addressed about the origin and evolution of Antarctic lithosphere are: • What was the role of East Antarctica in Precambrian continental growth processes? o Because East Antarctica occupied the center of early supercontinents such as Rodinia and Gondwana, and may represent ~15% of Earth’s Precambrian crust, it holds a key to understanding the processes governing continental growth spurts in the late Archean to Latest Neoproterozoic and issues such as the role of magmatism, accretionary and collisional tectonics, continental break-up, and subduction in early continental Earth history. 5 • What are the origins, extents and ages of interior basins? o Tectonic, erosion, subsidence and glacial history can be determined by knowing the age, lithology and 3-d geometry of sedimentary basins in East Antarctica. • What are the distribution, magnitudes, and focal mechanisms for earthquakes? o A lack of seismic data limits definition of lithospheric structure and neotectonics. • What is the timing and magnitude of Mesozoic to Cenozoic extension in Antarctica and its effect on the global plate motion circuit? o Extension in the latest Mesozoic rifted Australia and New Zealand from Antarctica. Study of the timing of extension, uplift and magmatism provides a means to determine mechanisms of continental breakup and relative motion between East and West Antarctica. o Rates of extension and lithospheric thinning have a direct influence on magma production rates and volcanism; however, the higher production rates in the late Cenozoic do not appear to be the result of higher rates of extension. 3. Geodynamics of rifting in an ice-covered environment. Understanding lithosphere geodynamics in Antarctica’s ice-covered environment will clarify its feedback on other global systems. • What are the feedbacks between mountain uplift and ice sheet and climate models? o Preliminary ice sheet modeling studies suggest the Gamburtsev Subglacial Mountains are the likely location for initiation of the East Antarctic ice sheet and therefore, could be a key factor in

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