POR FISIÓN; DATACIÓN POR HELIO; DATACIÓN POR PLOMO ; en el am- biente acuático. datación por potasio-argón Método para determinar la edad. Request PDF on ResearchGate | Cronologia potasio-argón del Complejo Efusivo Copahue-Caviahue, Provincia del Neuquén Potassium-Argon chronology of. d Kalium e potasio potassium-ammonium chloride; potazote () argon d Kalium – Argon Alterbestimmung e datación con potasio – argón

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Petrographic data, reported in a subsequent section of this paper also suggest two periods of folding for this region.

The premetamorphic lithologies were limestones and quartzarenites, both of which contained aluminous clays. Lithic fragments are large 0.

Hematite 1 to 2 percent is less abundant than limonite and occurs as elongated, feathery masses, Iying paraIlel to planes of foliation. Argno Ages Both Mapes Vazquez op. Fine-grained quartz 35 to 45 percent with sutured borders compases the groundmass of most of the phyllites.

The marble and the quartzite are essentially monomineralic, but sericite 5 to 10 percent is lotasio present in both and locally is abundant in the marble. Calcite ranges in grain size from less than 0.

dstacion Plagioclase feldspars are the most abundant mineral in the diorite, accounting for 50 to 70 percent of the rock. Midland, West Texas Geol. Five analyzed samples of diorite Table 4 show that major and minor element concentrations vary considerably among themselves and with respect to the average composition of andesite Nockolds, Relict sedimentary textures generally are not present in either the marble or the quartzite.


Layer: Dataciones (ID: 3)

The metasediments are intruded by a shallow diorite dataciion. Additional metamorphic textures of these higher grade rocks include cataclastic texture and the development of foliation. Since contacts between some units are gradationaI and the structures complicated, thicknesses are only approximate.

The largest and best exposured outcrop of metaconglomerate appears to be in fault contact with the dataciion quartzite and phyllite. Olivine is rare in the diorites, and its positive identification was made only in a few thin sections. X-ray diffraction patterns were run for all the plagioclase.

Two periods of folding are supported, however, by lenses of marble occurring conformably within the phyllites of Arroyo Talamantes, which show two directions of folding within a single hand specimen. Since the potasil range of these bivalves makes them undesirable for correlation, the validity of this age is questionable from a paleontological standpoint.

Acknowledgments The authors are grateful to Dr. Porphyroblasts are unaltered, free of inclusions, and have straight extinction. The earIy Paleozoic metasedimentary rocks in Mexico are believed to belong to two separate tectonic belts bordering a central eatacion and metamorphic cratonic backbone Guzman and de Cserna, op.

Almost all the phyIlites examined in thin section possess arggon direction of foliation, as evidenced by the parallel alignment of micaceous minerals. These phases are contained in a matrix of very fine-grained 0. The alternative of only a single deformation is less well suported by the present data and by the regional geologic history of Mexico, which documents at least two orogenic events after the deposition of the La Pimienta Phyllite, one probably during the very end of the early Jurassic and a second during the Late Cretaceous-Early Tertiary de Cserna, The thickness of these layers ranges from 1 to 4 cm.


Rcliet quartz grains show a variety of extinction types, ranging from undulose to straight, and contain minute inclusions.

Datación Potasio-Argón (K-Ar)

The contortion and weathering make accurate structural measurements difficult lo obtain, but generally the foliation strikes north-south with moderately steep dips to the east and to the west. Bioclasts or even recrystallized bioclasts appear to be absent in the foliated and nonfolialed marble.

According to Dengo op. Above the Iowermst unit in the section is Unit B, which is composed of three distinct members, designated i, i i, and i i i, with a total thickness of m. In rocks showing more advanced recrystallization, quartz grains are smalIer and exhibit sutured boundaries and Boehm lamellae.

The concentration of water was determined for selected samples by a modification of the Penfield method Shapiro and Brannock, Porphyritic diorite is present but rare. The Las Pilas Diorite has the charachteristics of a hypabyssal intrusion. The late Paleozoic age assigned to the lowermost La Pimienta phyllite by Burckhardt op. Both minerals are fine grained and occur with sericite. UNIT C Interbedded fine-grained, grayish-purple and grayish-orange phyllite; contains lenses of marble dtacion metaconglomerate.