摘要:

A 57,000 line kilometer, high‐resolution aeromagnetic survey was flown in 1987 as a contribution to the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE). Existing aeromagnetic data from the United States and Canada were combined with the new data to produce a composite map and gridded data base of the Lake Superior region (Figure 1).Analysis of the new data permits more accurate definition of faults and contacts within the Midcontinent Rift system (MCR). The aeromagnetic map provides important information supplemental to the seismic profiles acquired under the GLIMPCE program in 1986, allowing lateral extension of the seismic interpretation. In particular, modeling of the data provides an independent assessment of a reflection seismic model derived along line A (Figure 2). The profile and gridded digital data are available to geoscientists through the Geophysical Data Centre of the Geological Survey of Canada (GSC), while the gridded data are available from the USGS‐EROS Data Center.GLIMPCE was established in 1985 to study the nature and genesis of the crust in the Great Lakes region. Program participants include the GSC, the U.S. Geological Survey (USGS), provincial and state surveys, and Canadian and American universities. In the Lake Superior area, a major objective of the program is to develop thermal, tectonic, and petrogenetic models for the evolution of the MCR and to evaluate these in the broader context of the tectonic evolution of the North American continent.Pre‐1982 geological and geophysical knowledge of the MCR in the Lake Superior region has been summarized byWold and Hinze[1982]. The Lake Superior region provides a unique window on this Proterozoic rift system, exposing igneous rock of the Keweenawan Supergroup that disappears under Paleozoic cover to the sout

ISSN:0002-8606    

DOI:10.1029/90EO00052

年代:1991

数据来源: WILEY

摘要:

The redefinition of the horizontal geodetic control network in North America is the subject of a recently published book by the National Oceanic and Atmospheric Administration's National Geodetic Survey. North American Datum of 1983 (NOAA Professional Paper NOS 2) covers the history of the project from its inception in 1978 to completion of the redefinition in 1988.The 256‐page report is intended to serve as a record of what was actually done during the new datum project, which was a cooperative effort supported by the United States, Canada, Denmark, and Central America. The report describes the actual execution, including the inventory of data used, the laborious task of building the data base, the computations themselves, and the datum implementation activitie

ISSN:0002-8606    

DOI:10.1029/90EO00054

年代:1991

数据来源: WILEY

摘要:

Brent Dalrymple makes a compelling plea for a “marriage between science and the media” (Editorial, January 29, 1991), but I'm not sure whether either of the blushing parties would enjoy holy matrimony. Work harder to understand each other? By all means, yes. But marriage? Emphatically no! We can labor together to inform the public most effectively without resorting to cohabitation, sanctified or otherw

ISSN:0002-8606    

DOI:10.1029/EO072i008p00084-01

年代:1991

数据来源: WILEY

摘要:

British scientists at a January 11 meeting of the Royal Astronomical Society were asked to consider a proposal to license commercial use of the International Geomagnetic Reference Field (IGRF). The income—which could reach over $2 million a year—would support geomagnetic observatories in developing countries. The proposal would not affect the access that research scientists presently have to the data free of charge.IGRF has become the industry standard for all kinds of navigation, including that of airplanes and radio systems. In oil production, it is used for the highly accurate magnetic tools that direct bores. Even with modern navigational devices, the risk associated with mid‐direction makes magnetic reference more critical than ever, if only as a fail‐safe

ISSN:0002-8606    

DOI:10.1029/EO072i008p00087-03

年代:1991

数据来源: WILEY

摘要:

The global mid‐ocean ridge system is a primary focus for energy transfer from the Earth's interior to the lithosphere, biosphere, hydrosphere, and atmosphere. In a coordinated effort to understand the causes and predict the consequences of mantle‐driven physical, chemical, and biological fluxes through the ridge‐crest system, the RIDGE (Ridge Inter‐Disciplinary Global Experiments) Initiative will launch in 1991 a series of integrated studies of the mid‐ocean ridge “RIDGE Steering Committee, 1989”.Seafloor observatories will be developed for monitoring temporal variation in active hydrothermal and volcanic systems on a decadal scale. Innovative seafloor instrumentation and work systems will perform physical, chemical, and biological measurements and sampling to address covariation among magmatic, tectonic, hydrothermal, and water‐column components of the ridge‐crest system. Initial studies may be focused on the

ISSN:0002-8606    

DOI:10.1029/EO072i008p00090-03

年代:1991

数据来源: WILEY

摘要:

What are the processes that drive magmatic diversity? How is it that volcanic centers can exist for millions of years erupting a variety of chemical types? What are the means by which large batholithic complexes become assembled? Magmas (silicate melts)differ from other geophysical fluids, such as oceans and atmospheres, in that their physiochemical history is largely governed by the processes of solidification and melting. This yields a system with strongly varying physical properties where bouyancy can be generated in complex ways. Much of the recent progress has come from numerical and experimental work specifically directed at the complex interactions of multicomponent systems undergoing phase changes and transport. Geochemical studies also indicate that magmatism is the result of thermal and chemical perturbations on a crustal scale.

ISSN:0002-8606    

DOI:10.1029/EO072i008p00091-03

年代:1991

数据来源: WILEY