Structural Geology and Tectonics Division -- Support for Research in Tectonics at NSF

This document (submitted July 24, 1998) states the position of the Division of Structural Geology and Tectonics, whose 1500 members belong to the Geological Society of America, a professional organization for earth scientists. We direct our comments to the management of the Geosciences Directorate, the Division of Earth Sciences, and the Division of Ocean Sciences in NSF, and also to the committees charged with addressing plans, such as GEO 2000, for research opportunities in NSF.

We contend that any new long-range plans for Geosciences at NSF must advocate continued and readily identifiable support for research in tectonics.

The record shows that advances in tectonics are achieved when research support is provided through small grants to individual PI's (e.g., Tectonics Program) and through large grants to several PI's (e.g. Continental Dynamics Program).

A White Paper from the Division of Structural Geology and Tectonics, Geological Society of America:

PREAMBLE

This document states the position of the Division of Structural Geology and Tectonics, whose 1500 members belong to the Geological Society of America, a professional organization for earth scientists. We direct our comments to the management of the Geosciences Directorate, the Division of Earth Sciences, and the Division of Ocean Sciences in NSF, and also to the committees charged with addressing plans, such as GEO 2000, for research opportunities in NSF.

We contend that any new long-range plans for Geosciences at NSF must advocate continued and readily identifiable support for research in tectonics.

The record shows that advances in tectonics are achieved when research support is provided through small grants to individual PI's (e.g., Tectonics Program) and through large grants to several PI's (e.g. Continental Dynamics Program).

This report outlines the basis for our position. We begin with a definition of tectonics and a brief review of how its fundamentally cross-disciplinary and integrative nature places it at the heart of the earth sciences. We then summarize several areas of exciting research presently underway, each of which offers opportunities during the next five to ten years for major advances in our knowledge about earth processes and history. This document is intended to convey the character of research in tectonics by means of a few examples; it is not intended to be an exhaustive or comprehensive survey of past, present, and future research.

DEFINITION AND SCOPE

Tectonics, as we use the term here, is the study of large-scale features in planetary lithospheres that have resulted from deformation. Thus, tectonics concerns the nature and origin of features that would be visible in a single glance at regional geologic maps, maps of the physical face of the earth, or images of planets and moons: for example, ocean basins and continents, regionally developed faults and systems of fractures, mountain ranges and topographically subdued shields, and volcanic arcs. Many tectonic features on the earth are immediately visible because they contribute to the physical appearance of the environment of life.

Research in tectonics seeks not only to characterize large-scale features but also to investigate the deformations, forces and displacements responsible for them. As such, tectonics is inseparably linked to structural geology , which is the study of deformation at all scales. Research in tectonics has always been distinguished by two additional attributes, regardless of the size or scope of a particular project. First, it is inherently multidisciplinary and integrative, and, like the Greek tecton, or builder, it employs diverse tools. To study, for example, the growth and decay of mountainous topography, we need to investigate not only the forces and displacements at relevant plate boundaries, but also phenomena as diverse as the influence of climate on fluvial erosion and the influence of orogenic topography on local precipitation and global climate.

Second, tectonics encompasses the whole of geologic time, from the early history of the earth and solar system to the immediate present. If our goal as earth scientists is to explain large-scale features, then we need to complement studies of active, on-going tectonic processes with investigations focused on the geologic record of past events. For example, geodetic, geophysical, and geomorphological studies of the Himalaya are providing data on present rates of deformation, uplift, and erosion, which can be compared with rates predicted by geodynamic models. The Himalaya, however, preserve a rich record of subduction- and collision-related deformation and magmatism extending back tens of millions of years. The character and disposition of the active present-day chain and of most other tectonic features for that matter are partly determined by its earlier tectonic history.

To summarize:

Tectonics concerns the characterization, origin, and evolution of large-scale features of planetary lithospheres.

Tectonic processes have modified the lithosphere throughout geologic time. Investigating them requires studies of not only active environments but also the geologic record of ancient events.

Research in tectonics is inherently multidisciplinary and is not restricted to either the marine or terrestrial realm. This multidisciplinary approach characterizes not only larger multi-PI projects but also most of the smaller, single-PI projects.

EXCITING RESEARCH AREAS AND POSSIBLE FUTURE DEVELOPMENTS

We present below seven examples of research activities in tectonics that have developed rapidly during the past decade and which hold promise for further advances during the next five or ten years. This selective list illustrates and exemplifies the multidisciplinary nature of research in tectonics. Some of these areas owe their rapid development to technological achievements, such as the wide availability of inexpensive, portable Global Positioning System (GPS) receivers. Some reflect novel and fruitful collaborations or the introduction of new ideas. The visibility and impact of research in these areas is demonstrated by the regular publication of articles and papers in Geology, Geophysical Research Letters, Nature, and Science.

1. Rates and patterns of deformation

More precise geodetic measurements using GPS are providing present-day rates of displacements in actively deforming areas. The next decade will see closer collaboration among field geologists, geodynamic modelers, and seismologists, which will result in better assessments of seismic hazards of large regions.

Every earth scientist studying a mountain chain or major structure has probably wondered, "How fast?" Tectonicists of all stripes want to know if models for plate motions can be confirmed with observational data. In a little over a decade, GPS has matured to where it can provide ever more precise answers to these and a host of other fundamental questions. Geodesy is serving as the bridge linking models for plate velocities, which largely derive from oceanic hot spots, with observed rates of horizontal and vertical movements on the continents. In the next decade, improvements in the ease of use of geodetic equipment and in the precision of horizontal and vertical measurements will allow routine study of structures within plate-boundary zones. This research will provide direct information about processes that at present remain inaccessible or difficult to study, such as seismic coupling, transfer of slip between structures, and the relationship of blind faults to surface folding.

2. Rheology of crustal faults

Improved laboratory apparatus allow new kinds of experiments on natural and simulated fault rocks. These studies, which demonstrate that earthquakes result from unstable frictional sliding, have led to provocative models for seismogenic behavior of tectonic faults. In the next decade, results from structural field studies, experiments, and possibly drilling in active faults will collectively be used to test these models.

Complete characterizations of the deformational behavior of earth materials, whether they are at the surface, in the crust, or in the mantle, require experimentally investigating their rheology. Recent technological advances allow experiments that better simulate conditions in the earth. For example, materials can now be deformed to higher strains under more realistic strain geometries and pore-fluid conditions. In the past decade, experiments have addressed the basic question of why slip on upper crustal faults ranges from aseismic to seismic, and why active faults like the San Andreas in California are apparently weaker than mechanical models predict. Lab studies of fault rocks like gouge and pseudotachylite indicate that frictional sliding may vary from stable and aseismic, to unstable (stick-slip) and seismogenic. In the future, collaborations among experimentalists and field geologists, who investigate active and ancient tectonic-scale faults, will yield empirically confirmed models for slip on upper crustal faults.

3. Mountains and climate

New models for the growth and decay of mountainous topography incorporate the effects of climate, surface processes such as erosion and mass wasting, and stresses related to plate boundaries. Multidisciplinary teams are seeking to explain seemingly unrelated phenomena, such as how the uplift and exhumation of deeply buried metamorphic rocks might be related to patterns of erosion.

In the past decade, a re-phrasing of the "chicken-or-egg" puzzle has revolutionized research into the origin and evolution of mountain belts. Does climate change drive mountain building, or does mountain building drive climate change? We are now no longer content simply to model convergent orogens as accretionary wedges that grow entirely in response to plate subduction. Observational evidence and powerfully predictive models both suggest that surface processes influence not only the topographic form of mountain belts and massifs, but also attributes as diverse as the history of uplift, the nature of internal structures, and the internal disposition of metamorphic rocks. Interdisciplinary teams will address the coupled tectonic-geomorphologic problem in active chains, where present-day rates of erosion and deformation can be measured, and in ancient orogens, where the effects of long-term surface and tectonic processes are visible.

4. Tectonic reconstructions in Deep Time

A burgeoning interest in how, when, and in what forms life originated on earth is forcing renewed investigations into the configuration of continents and ocean basins in early and pre-Phanerozoic time.

As earth scientists, we naturally are curious about the entire histories not just the past million years or so of our home planet and its kin in the solar system. Because the direct marine record of plate tectonics on earth only extends back to about 190 Ma, reconstructions of the positions of the continents in earlier times are more difficult to support empirically. Nevertheless, paleobiologists and astrobiologists have cast the spotlight on tectonics. They want to know the disposition and character of continents and oceans in what we call Deep Time, extending back from the early Phanerozoic Era. We now have models proposing that unusually rapid changes in plate configurations might have coincided with the explosion of life forms about 560 - 600 m.y. ago. In the next decade, we can expect new, empirically sound continental reconstructions that will be advanced by the combination of geologic mapping, high-resolution isotopic dates, and paleomagnetic data.

5. Punctuated, non-linear tectonic evolution

Earth's history might have been punctuated by short-lived, "catastrophic" tectonic events that had profound effects on its atmosphere and hydrosphere, and on life itself. The frequency and causes of these events will be addressed using marine and terrestrial records of earth history.

The bolide-impact hypothesis for the extinctions at the Cretaceous-Tertiary (K-T) boundary has had the unintended consequence of reawakening our appreciation for the possibility that earth's tectonic evolution has not been linear or steady-state, but rather punctuated by catastrophic events. Investigations on land and in the oceans are adding to the existing record of tectonic instabilities: the Late Cretaceous superplume, voluminous but short-lived volcanism at divergent plate boundaries and within plates, the Precambrian anorthosite event, and, more speculatively, rapid episodes of true polar wander. Whatever the physical basis and causes of these events, these models of catastrophic tectonics will spawn deductions of their system-wide effects on the earth's atmosphere, hydrosphere, and biosphere.

6. Three-dimensional visualization and imaging

Rapid technological advances now allow three-dimensional computer-aided renditions of rock bodies and structures, and the combinations of virtually any kinds of geologic and spatial data on a map base. The Internet and the widespread availability of work-station computers will allow much greater circulation and use of map-based data, which in turn will generate a greater demand for high-quality geologic mapping.

Tectonic syntheses, which are based on diverse types of data and evidence, are conventionally reported using two-dimensional geologic maps and cross sections. Visualizing the three-dimensional disposition of rock bodies and structures has been left up to the user. Several technological advances are revolutionizing the acquisition of spatial data and the portrayal of geologic and physiographic features in three dimensions. Basic geologic data can now be acquired in the field in digital format. These can constitute part of a geologic spatial database, which can be digitally manipulated and combined with diverse geographic, cultural, and topographic databases or laid onto satellite imagery. The geologist or land-use planner can produce whatever kind of map suits the purpose at hand. In the next decade, as software becomes more accessible and intelligible to academic researchers and students, three-dimensional renditions of surface and subsurface geology on the computer screen in the classroom and research lab will become the norm rather than the exception.

7. Natural tectonic laboratories

A few regions on earth have come to be considered as natural laboratories, each epitomizing a particular tectonic history or process. Additional natural laboratories will be developed where multidisciplinary studies can illuminate other tectonic settings.

A natural tectonic laboratory can be thought of as a region on a continent, in an ocean basin, or crossing the shoreline where a certain tectonic process is especially amenable to study. Each is further distinguished by two attributes. First, advances in knowledge can be gained by research projects of widely varying scope, from those directed by a single PI to those involving many PI's, and in all cases using a wide range of tools and disciplines. Second, the ideal laboratory allows the investigation of a process as it has acted over different time scales: historic (10² years); Recent (10⁴ years); Quaternary (10⁶ years); and late Cenozoic (10⁷ years). All these time spans are relevant to understanding active tectonics. Data from laboratories in modern tectonic settings can be supplemented with information obtained from well-exposed and particularly illustrative ancient orogens, whatever their age. Well-known laboratories, which have been subjected to extensive geophysical, geochemical, and geological studies, include: the San Andreas fault of California and the Alpine fault of New Zealand as continental transform faults; the Himalaya and Taiwan as collisional accretionary wedges; and the Basin and Range province of the western United States as an extensional orogen. The next decade will see natural laboratories developed in orogenic chains in plate interiors, and in plate-boundary zones featuring strongly partitioned displacements.

Ad-Hoc Committee of the GSA Division of Structural Geology and Tectonics
July 24, 1998
Darrel Cowan, University of Washington, Chair
Mark Brandon, Yale University
Eldridge Moores, University of California, Davis
Terry Pavlis, University of New Orleans
Jan Tullis, Brown University