The Geomagnetic Field Over the Last 5 MYR from Lava Flows, and, Properties of the Venusian Lithosphere from Magellan Data.

Details The Geomagnetic Field Over the Last 5 MYR from Lava Flows, and, Properties of the Venusian Lithosphere from Magellan Data. The Geomagnetic Field Over the Last 5 MYR from Lava Flows, and, Properties of the Venusian Lithosphere from Magellan Data.

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........17j&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SAN DIEGO, 1994.Source: Dissertation Abstracts International, Volume: 55-12, Section:

Computer Science

1

Scientific paper

The dissertation consists of two unrelated parts. Chapters 2 and 3 investigate long-term properties of the geomagnetic field. Chapters 4-6 are studies of Venus using data from the Magellan mission. Chapter 2 presents a new database comprising palaeomagnetic directions from lava flows over the past 5 Myr. Existing palaeosecular variation models fail to take account of time-averaged field structure and do not adequately describe the properties of the database. In chapter 3 regularized models of the time-averaged field are constructed from Brunhes, normal and reverse polarity subsets of the new database. Non-zonal models are required to fit the data. Normal and reverse stable polarity field structures are significantly different. Normal polarity field models are similar to historical field maps; differences may be real or due to data quality and distribution. Jackknife estimates of the models suggest that data from a few sites contribute significant structure; removing these sites yields conservative estimates of the time-averaged field. Chapter 4 presents an investigation of polygonal fracture patterns observed in radar images of volcanic plains on Venus. The patterns are similar to jointing in lava flows on Earth, but the scale of the venusian networks is much larger than their terrestrial counterparts. The venusian networks may be the result of increased heat flux to the base of the lithosphere, during the formation of flood basalt provinces. Chapter 5 is a study of topographic flexural features on Venus. These are modeled using a thin-elastic plate model. Reliable estimates of mechanical lithospheric thickness are in the range 21-37 km. Dynamical models predict a thick viscous lithosphere. Numerical simulations are used to explore the validity of a 2-D cartesian approximation to an axisymmetric load geometry. Chapter 6 presents a preliminary resolution analysis of Magellan cycle 5 gravity data. Multi-taper spectral coherence estimates show the best resolution available from the Doppler residuals to be 450-500 km. Thus in some regions it should be possible to distinguish between local compensation, flexural or dynamic support of topography.

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