The geologic province and thermo-tectonic age maps were compiled in 1997 to ensure a consistent method of providing values for these two parameters. The maps depict only features approximately 150 km across and greater due to the fact that the resolution of the maps should be consistent with the resolution of the seismic refraction data.
Geologic Province Map
A geologic province is defined as "any large area or region considered as a whole, all parts of which are characterized by similar features or by a history differing significantly from that of adjacent areas" (Glossary of Geology, 1980). We divide geologic provinces into six main categories: shield, platform, orogen, basin, large igneous province, and extended crust. (We use sub-categories for some province types, but, for simplicity, do not include them in the displayed map.) Histograms help us to understand the relationship between tectonic history and crustal structure.
Age of Last Thermo-Tectonic Event
Thermo-tectonic age (or, age of the last thermo-tectonic event) refers to the age in which the last major event to influence the crustal structure took place. This event is generally consistent with the geologic province. It is assumed that, in the time since this event took place, the crustal structure was not significantly modified by more recent tectonic events, although cooling processes will have effected some crustal parameters through time. This study of the relationship between thermo-tectonic age and crustal structure is the first of its kind. You can see some of the results in the form of histograms of crustal thickness vs. thermo-tectonic age. Contrary to earlier thought, there is little change in mean crustal thickness before the Cenozoic and Mesozoic.
|Cenozoic and Mesozoic||0-245 Ma||245 m.y.|
|Paleozoic||245-570 Ma||325 m.y.|
|Late Proterozoic||500-900 Ma||400 m.y.|
|Middle Proterozoic||900-1600 Ma||700 m.y.|
|Early Proterozoic||1600-2500 Ma||900 m.y.|
|Archean||> 2500 Ma||--|
References and Acknowledgments
- The Tectonic Map of the World by Exxon (1985) was the main source of information to classify geologic provinces and thermo-tectonic age in the Phanerozoic.
- The maps 'Seismicity and Tectonics of Stable Continental Regions' of the project 'Earthquakes of Stable Continental Regions' by EPRI (1994); Precambrian Geology (Goodwin, 1991); and Principles of Precambrian Geology (Goodwin, 1996) were the main sources of information to classify regions of Precambrian thermo-tectonic age.
- Additional information was provided by:
- A.V. Peive, and A.L. Yanshin (eds)., Tectonic Map of Northern Eurasia (1980), Akademia nauk, SSSR;
- M. Downes and J. Simmonds (comments on Australia);
- A. Grantz (comments on the Arctic);
- W. Hamilton (comments on Australia, Indonesia and North America); and
- S. Kostiachenko (comments on Asia and Siberia)