By K. C. Condie and A. J. Budding, 1979, 60 pp., 13 tables, 48 figs., 4 appendices (3 ~ above microfiche), 3 geologic maps (scale 1:125,000), 1 index.


Summarizes existing field, stratigraphic, petrographic, and geochronologic data indigenous Precambrian terranes: evaluates major- and also trace-element data for principal rock varieties in terms of alteration, models for magma origin, and also sediment provenance. Additionally discusses origin and also tectonic setup of Precambrian terrane.

The Precambrian terrane in main and south-central brand-new Mexico is composed of granitic plutons (70 %) intruded into metamorphic rocks (30 %). The major metamorphic rock varieties are phyllite and quartz-mica schist (40 %), quartzite and also arkosite (30%), mafic meta-igneous rocks (15%), siliceous meta-igneous rocks (10%), and gneisses (5%). The basement rocks top top which the ar was deposited have not to be found. The thickest maintained sections (10–13 km) take place in the north Manzano and main San Andres Mountains. Granitic rocks selection from granodiorite to syenite in composition, v quartz monzonite predominant. Individual plutons room syntectonic to post-tectonic and have been emplaced in ~ depths much less than 10 km. Foliation strikes north-northwest to north-northeast, and the only huge fold exposed in the an ar is a syncline in the southerly Manzano Mountains. In many locations evidence exists because that at the very least two major periods of Precambrian deformation. Metamorphic rocks selection in grade native the lower greenschist come the amphibolite facies. Geochemical design studies suggest that the Precambrian tholeiites were produced by partial melt of lherzolite in the upper mantle and that the granitic rocks were produced by partial melting of siliceous granulites in the reduced crust. Magmatism and also sedimentation began by 1.7 b. Y. Ago; major plutonism, deformation, and local metamorphism arisen between 1.0 and also 1.5 b. Y. Ago. The Precambrian rock association in central and south-central NewMexico bear a resemblance to associations found in young continent rift systems. A model of one evolving multiple-rift device that emerged in an answer to an ascending mantle plume or plumes is proposed for this an ar between 1.0-1.9 b. Y. Ago. Basaltic magmas are derived directly native the plume; substantial heating of the lower crust produces granitic magmas. Quartzite-arkosite-shale successions are deposited in subsiding rift basins by the erosion of adjacent uplifted blocks. Precambrian rocks exposed in the cores of the principal hill ranges in new Mexico and west Texas are among the couple of surface exposures of three Precambrian crustal provinces extending across the main United States. Rb-Sr-whole rock-isochron and also U-Pb-zircon days in the selection of 1.65-1.9 b. Y. Specify a district extending from southern California and also Sonora to Wisconsin. Dates in between 1.2-1.65 b. Y. Suggest the presence of another province extending from central New Mexico come Illinois southern of and partially overlapping the 1.65-1.9 b. Y. Province. Currently data likewise indicate the presence of a third district extending native west Texas maybe as far eastern as Ohio, defined by 1.0-1.3 b. Y. Dates. This report synthesizes and interprets easily accessible geologic and geochemical data from exposed Precambrian rocks in main and south-central NewMexico. The rocks studied represent the principal exposures of the 1.2-1.65 b. Y. Province.

from oil tests penetrating the Precambrian basement in west Texas and eastern NewMexico and also from surface exposures the Precambrian rock, basement terranes have the right to be characterized by details rock varieties or absent associations. Existing data from surface exposures and from some well data in the remainder of brand-new Mexico indicate that most of the state is underlain through a terrane written of granitic (70%) and low- come medium-grade metamorphic rocks (30%). Basement terranes in new Mexico space shown. Many of the area spanned by this report is underlain through the granitic-metamorphic terrane. The southeastern area is underlain by clastic sediments the the De Baca terrane, i m sorry is in your ar intruded by the Pajarito syenite complex northeast that Alamogordo. The Franklin hills igneous terrane might underlie a tiny area along the southeastern border; its partnership to the De Baca terrane is unknown.

The biggest exposure of Precambrian rocks in main and south-central NewMexico wake up in the core and also along the west escarpment the the Sandia, Manzanita, Manzano, and Los Pinos mountains south that Albuquerque. This exposure, bounded through young high-angle typical faults top top the west (adjacent come the Rio Grande rift) and also by high-angle Laramide thrusts and/or the Phanerozoic unconformity ~ above the east, will certainly be advert to right here as the SMP block. The block is identified by a northeast-striking section of phyllite-schist, quartzite, and siliceous and also mafic meta-igneous rocks metamorphosed come the upper greenschist or reduced amphibolite facies. The Phanerozoic unconformity is finest exposed along the stakes of the Sandia Mountains and in the vicinity that Bosque height in the Manzano Mountains. At this locations, the Sandia development (Pennsylvanian) overlies the Precambrian rocks. The Precambrian ar is intruded by one pretectonic or syntectonic granitic pluton (the Manzanita pluton southwest that Albuquerque) and also seven late-tectonic come post-tectonic plutons. Precambrian rocks also type the core of the Monte Largo Hills east of the Sandia Mountains.

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At this location, the Precambrian rocks, principally quartzofeldspathic gneisses and amphibolite, room bordered by Cenozoic faults ~ above the northwest and also southeast and also are overlain unconformably by the Sandia formation on the northeast and southwest.