From a study of the major tectonic features--Precambrian outcrop, post-Precambrian metamorphic outcrops, major intrusives, eruptive centers, folds and fold belts, and fractures and faults--of an area in the

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western hemisphere bounded by latitudes 40°N and 14°S and longitudes 60°W and 108°W, it is concluded that this part of the earth's crust has been segmented into major blocks bounded by wrench fault zones. The absence of "island arcs" in this area is noted. Four occurrences of triangular crustal "building blocks" bounded on two sides by wrench-fault zones and on the third by autochthonous fold belts are pointed out, as are other recurring crustal components.

An interpretation of basement faulting based on the application of the principles of wrench-fault tectonics to observed tectonic features leads to the conclusion that the observed tectonic pattern of Middle America can have resulted from the interplay of essentially meridional crustal compression and equatorial compression, both of which are thought to have been active throughout geological time.

There is a clear relation between the distribution of oil and gas provinces and the basement tectonic pattern.

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