A deep drill hole recently completed on the Central basin platform of west Texas provides a rare look at almost 5 km of basement rocks. Most of the crystalline rocks encountered were basic and ultrabasic in composition. A variety of geophysical data is available from the bore hole and vicinity. The petrographic and geophysical data suggest that a large, layered, basic intrusion was penetrated by the well. Geochronologic (U-Pb) data indicate an age of about 1.1 Ga for this intrusion. This date has significant tectonic implications because it indicates that commonly accepted analogies with the southern Oklahoma aulacogen (550 Ma rifting) are not valid. However, it is interesting to note that this feature formed during another widespread period of rifting (Keweenawan).

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