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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 681

Last Page: 682

Title: Geochronologic Evidence for Paleozoic Plutonic Activity in Florida Mountains, New Mexico: ABSTRACT

Author(s): D. G. Brookins

Article Type: Meeting abstract

Abstract:

Plutonic rocks of the Florida Mountains, New Mexico, have been mapped both as Precambrian and as Mesozoic. Corbitt and Woodward demonstrated that the Floridas are bisected by the southern Cordilleran thrust belt, and Brookins reported Precambrian Rb-Sr dates from south of the thrust for granitic rocks while alkali granites-syenites from north of the thrust yielded scattered,

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apparent dates ranging from Precambrian(?) to Paleozoic(?). R. E. Denison had earlier determined K-Ar and Rb-Sr mineral dates from the northern rocks to range from approximately 380 to 550 m.y.B.P., although these dates were considered spurious as plutonism in southern New Mexico has conventionally been assumed to be either Precambrian or Mesozoic-to-early Tertiary. Field relations for the northern block suggest some alkali granites-syenites are intrusive into the Bliss Formation (Cambrian-Ordovician) but younger than mid-to-late Paleozoic rocks, although the intrusive contacts have been questioned. New major and trace element chemical studies indicate a transition from alkali granite to syenite for the northern block and, more important, fresh material from drill cores has yielded Rb Sr whole rock ages of 378±19 m.y.B.P. (alkali granite suite) to 423±24 m.y.B.P. (syenite suite) with a composite date of 405±18 m.y.B.P. This age confirms Denison's work and argues for previously unrecognized Paleozoic plutonism in southern New Mexico, although it is not known at present whether this date represents a western extension of Ouachita-dates (i.e., parallel to the Texas lineament) or a separate, isolated event. Regardless, other apparent-Paleozoic dates from southern New Mexico must now be reexamined in light of the dates from the Floridas.

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