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Dive into the research topics where Marcia K. McNutt is active.

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Featured researches published by Marcia K. McNutt.


Geochemistry Geophysics Geosystems | 2000

A shallow, chemical origin for the Marquesas Swell

Marcia K. McNutt; Alain Bonneville

[1]xa0Young hotspot volcanoes within plate interiors are frequently surrounded by smooth, broad regions of shallow seafloor termed midplate swells. These swells are typically hundreds of kilometers wide and can be more than a kilometer in elevation. The most frequently invoked explanation for these swells is that they represent the thermal and dynamic surface uplift from rising mantle plumes. Here we argue that buoyancy of a volcanic unit underplating the Marquesan volcanoes just below the Moho, as imaged by a seismic refraction experiment, is capable of producing much, if not all, of what has been previously interpreted as a thermal swell in both the bathymetry and the geoid. The shallow compensation depth previously calculated for the swell based on geoid observations is thus expected given that the compensation resides at 20-km depth. The volcanic unit underplating the islands would also be expected to have a thermal effect, but its contribution to swell uplift is never more than 10% of the chemical contribution. The predicted increase in heat flow, on the other hand, is very large, but the thermal transient rapidly decays in the first 2 million years after emplacement. If similar large volumes of underplated material underlie other hotspot volcanoes, problems in explaining the lack of heat flow anomalies at later times and negligible rates of swell subsidence can be alleviated. Although volcanic underplating is unlikely to explain the entire swell signature for particularly large and wide swells, the results from the Marquesas suggest that at least some portion of hotspot swells may not be thermal in origin. After removing the geoid signature from the Marquesas volcanoes and swell, what remains in the geoid are stripes of amplitude 1 m and wavelength 650 km trending normal to the fracture zone. The anomalies are presumably relict from when this crust was created, but their amplitude is too large to be caused by variations in isostatically compensated crustal thickness.


Journal of Geophysical Research | 2004

Lithospheric deformation beneath the Altyn Tagh and West Kunlun faults from recent gravity surveys

Xiaodian Jiang; Yu Jin; Marcia K. McNutt

[1]xa0New gravity and topographic elevation data crossing the Altyn Tagh and West Kunlun faults in northern Tibet are used to test key features of a recently proposed tectonic model for the northern boundary of the Tibetan Plateau. The observations, collected in 1997 and 1998 at 468 stations along three profiles, were converted to Bouguer gravity anomalies to constrain flexural models for isostatic compensation of the large relief associated with these faults. Initially, we failed to reproduce the main features of the gravity anomalies with any isostatic model that assumes that the main contribution to the observed gravity anomalies is from the flexure of the Moho. By integrating sedimentary information derived from exploration seismology in the Tarim and Qaidam basins, we obtained satisfactory fits to the data using simple models of isostasy. No elastic strength across the Altyn Tagh is required to fit the gravity data, suggesting that the fault breaks the entire lithosphere beneath it and has negligible thrust component currently or in the past. This result is consistent with tectonic models that create the thickened crust of northern Tibet through thick-skinned thrust sheets progressively overriding Asia to the northeast as the Altyn Tagh, behaving as a classic transform fault, propagates in that direction. Farther west, the gravity observations across the West Kunlun are best explained by significant underthrusting of the high topography by an elastic plate with effective thickness between 30 and 40 km, in agreement with geologic interpretation and modeling of earlier, but very sparse, gravity observations.


Journal of Geophysical Research | 2007

Heat flow on hot spot swells: Evidence for fluid flow

Robert N. Harris; Marcia K. McNutt

[1]xa0We examine variability observed in heat flow determinations collected on hot spot swells. We find substantial scatter in heat flow at wavelengths of a few hundred kilometers and less at both Hawaii and Reunion, where closely spaced data exist, and large variability in the regional heat flow surveys at Cape Verde, Bermuda, and Crozet. Our preferred interpretation is that the observed variability is due to fluid flow. The presence of fluid flow admits the possibility that some heat is lost through advection such that the mean observed heat flow is less than the actual mantle flux. If so, the full magnitude of sublithospheric thermal variations may not be observed. This interpretation has important implications for understanding heat flow determinations made on hot spot swells and resulting geodynamic inferences. We suggest fluid flow may be masking variations in sublithospheric heat flux making available surface heat flow values a poor discriminator between geodynamic models for hot spot swells. Future field programs, methods of data analysis, and models should be designed to help extract a low-frequency mantle flux disguised by a high-noise surface filter.


Journal of Geophysical Research | 2004

Multiple episodes of volcanism in the Southern Austral Islands: Flexural constraints from bathymetry, seismic reflection, and gravity data

Kelsey Jordahl; Marcia K. McNutt; David W. Caress

[1]xa0At the southeastern end of the Cook-Austral Island chain, in the vicinity of the currently active Macdonald Seamount, multiple episodes of volcanism have left a diverse population of seamounts. Multichannel seismic reflection and shipboard gravity data provide observational constraints on the magnitude and wavelength of flexure, and multibeam bathymetry obtained by R/V Ewing and F/S Sonne within the study area provides full spatial coverage of all volcanic loads. Three-dimensional flexural modeling of closely spaced loads emplaced at discrete times, performed both with analytical models of idealized loads and with fourier domain solutions of the observed volcanic loads partitioned into the younger and older seamounts, is compared with seismic and gravity data. This modeling provides a more complete view of the volcanic history than radiometric dating and geochemical analysis of sparse dredge samples alone. Wide-angle seismic refraction data from ocean bottom hydrophones (OBHs) and expendable sonobuoys are also consistent with the flexural modeling results. Volume estimates of the different volcanic episodes show that one-half to two-thirds of the material added to the abyssal seafloor by midplate volcanic processes is due to older volcanism that erupted on young lithosphere, while the younger, higher seamounts contributed the remainder.


Geophysical Research Letters | 1998

Pacific-Farallon relative motion 42-59 ma determined from magnetic and tectonic data from the southern Austral Islands

Kelsey A. Jordahl; Marcia K. McNutt; Heather M. Zorn

PCT No. PCT/EP94/00296 Sec. 371 Date Aug. 8, 1995 Sec. 102(e) Date Aug. 8, 1995 PCT Filed Feb. 2, 1994 PCT Pub. No. WO94/18198 PCT Pub. Date Aug. 18, 1994The invention relates to new imidazoazines of the general formula (I) (I) in which R1, R2, R3, R4, R5, R6, A, D, E and G have the meanings given in the description, to processes for their preparation, and to their use as herbicides.


Geochemistry Geophysics Geosystems | 2000

Results of the Basin and Range Geoscientific Experiment (BARGE): A marine‐style seismic reflection survey across the eastern boundary of the central Basin and Range Province

Robert J. Brady; Brian P. Wernicke; Marcia K. McNutt; John C. Mutter; Gustavo P. Correa

Approximately 120 km of marine-style deep seismic reflection data were shot during a survey on the waters of Lake Mead in southeastern Nevada. The survey extends from near the abrupt eastern edge of the Basin and Range Province (BRP) to a point ~80 km into the extended domain. Data quality throughout the survey ranged from fair to poor; the recorded data include significant towing noise and occasionally problematic diffractions and sideswipe from canyon walls. The upper 2–4 s of the data shows well-defined reflections from sedimentary fill, but below that point, reflectivity is weak. Lower crustal reflectivity is generally absent under the eastern part of the survey, with a slight increase in reflectivity to the west. The reflection Moho appears as a series of weakly defined, discontinuous reflections, most of which occur at 10–11 s. A particularly interesting feature of the data set is the relative lack of reflectivity from the lower crust, which is a region of strong reflectivity on other seismic reflection data sets from the BRP.


Nature | 1999

Earth science: The mantle's lava lamp

Marcia K. McNutt

Studies of phenomena called hotspots and superswells, evident at Earths surface, offer the best clues as to the dynamic state of the underlying mantle. Their essential features have for the first time been reproduced in laboratory simulations of mantle convection scaled to Earth-like conditions.


Science | 2008

Scientific meetings: worth attending.

Marcia K. McNutt

As an ocean scientist concerned about ocean acidification and other environmental impacts from carbon emissions, I was interested to read B. Lesters News Focus story “Greening the meeting” (5 October 2007, p. [36][1]) for ideas on how scientists can reduce the carbon footprint of our professional activities. I thought his aim was off-target, however, when he set his sights on the Fall Meeting of the American Geophysical Union (AGU). This is the one time of the year that an international group of scientists from all fields relevant to climate science share their as-yet-unpublished results. Furthermore, the Fall AGU Meeting saves carbon dioxide, time, and money by eliminating the need for over 100 other separate gatherings (agency town halls, committee meetings, and workshops). In addition, more than 70 AGU committee meetings take place at the Fall Meeting, and it is an important venue for communicating with the press, including reporters from Science ! Indeed, we all need to look for ways to reduce our carbon emissions, but there are other ways to do it that dont sacrifice the unique contribution we can make to solving the problem as professional scientists.nn [1]: /lookup/doi/10.1126/science.318.5847.36


Eos, Transactions American Geophysical Union | 2008

McNutt Receives 2007 Maurice Ewing Medal

A. B. Watts; Marcia K. McNutt

It is a great honor for me to have the opportunity to deliver this citation for Marcia K. McNutt, the 2007 recipient of AGUs Maurice Ewing Medal. Marcia has made a significant contribution to our understanding of the structure of oceanic lithosphere, served in leadership roles in the marine scientific community, and instigated new directions and technologies for ocean exploration. n nMarcia received her undergraduate degree in physics and studied for the Ph.D. with Bob Parker and the late Bill Menard at the Scripps Institution of Oceanography. Her thesis led to two seminal papers on oceanic and continental isostasy. The first showed that flexure due to a young volcanic load could influence the subsidence and uplift history of nearby, preexisting volcanoes. This hypothesis, which explains why some seamounts and oceanic islands show uplift rather than subsidence, has had wide implications for basin development and sea level change. The second used 3-D spectral methods of analyzing topography and gravity data to argue that the Australian lithosphere responds to loads as a relatively strong structure at short time scales and a weak one at long geological times. This method is now widely used and is at the center of current debates concerning the rheology and strength of continental lithosphere.


Eos, Transactions American Geophysical Union | 2002

Isostasy and Flexure of the Lithosphere

Marcia K. McNutt

When I first began graduate work in geophysics nearly 30 years ago, there was, thankfully only a small body of written material I needed to read and comprehend prior to diving into my own research. Much has happened since then, and I often wonder how new graduate students today come up to speed in their areas of specialization. The answer is now obvious for any students undertaking research in broadly-defined areas involving lithospheric flexure and isostasy: they simply read Tony Watts new book.

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H. W. Menard

Scripps Institution of Oceanography

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Kelsey A. Jordahl

Woods Hole Oceanographic Institution

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Yu Jin

Chevron Corporation

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Xiaodian Jiang

Ocean University of China

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Alain Bonneville

Pacific Northwest National Laboratory

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Brian P. Wernicke

California Institute of Technology

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David W. Caress

Monterey Bay Aquarium Research Institute

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