This note summarizes the geologic occurrence and age measurements of high-grade metamorphic rocks from northern Colombia. These rocks crop out on the northern flank of the Sierra Nevada de Santa Marta near the southern shore of the Caribbean Sea. The Rb-Sr ages are in the range 1400 ± m.y., confirming the geological deductions of Gansser (1955) on their Precambrian age. As part of an uplifted remnant of the Guayana Shield, these gneisses suggest a great northwestern extension of the Precambrian shield beneath the younger sedimentary rocks of the low-lying llanos (plains) into the folded and uplifted Andes of Venezuela and Colombia. These Precambrian rocks lie close to the probable northwestern limit of the South American Precambrian cratonic basement.

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