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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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Bedding-plane cleavage and phyllitic sheen are prominent features, and the grain size averages 0. The possible second phase of folding and metamorphism detected in the rocks at Zacatecas is probably the result of some later period of Laramide activity. These eatacion are arranged with their long axes subparallel and are associated with rounded grains of quartzite.

Datación Potasio-Argón (K-Ar)

In general, this quartzite is nearly potaslo to the lenticular bodies of quartzite which occur in overlying units. The fracture cleavage is usually associated with microcrenulations.

For similar reasons minor amounts of chloritoid, which closely resembles some of the chlorites, may have escaped detection. The amount of sericite inereases and the grain size of the quartz decreases as the quartzite grades into the phyllite. Diorites displaying this subtle foliation and concordant contacts, have previously been interpreted as “greenstone lavas which are penecontemporaneous potasoo sediments” Burckhardt and Scalia, op. The rock is so fine grained that individual mineral grains are not macroscopically visible.

A report by Mapes Vasquez relics heavily on this early work and is concerned principally with the ore mineralization. Plotting of additional structural data may cause the two maxima described in Figures 4 and 5 above to merge into a single maximum. In northern Oaxaca a granitc-schist-pegmatite complex way also be of Precambrian age. Potassio 2 Optasio is equally inconsistent, ranging from 4. Morphotectonic units of Mexico after Dengo, These values refer to microphenocrysts alone because the groundmass plagioclase is too finee grained and generalIy too altered to allow compositional determinations.


Rock samples from Table 6 plotted on the AFM projection plane.

Datación potasio-argón (K-Ar)

Second, the Zacatecas “greenstones” do not appear to be volcanics but, instead, intrusive diorite related to a shallow pluton that intruded the Triassic metasedirnents. These ignimbrite sheets, which thicken substantially to the south, appear to have erupted at approximately the same time, Miocene-Oligocene Datacuon and McDowell,as the extensive ignimbrite sheets of the Sierra Madre Occidental Brown, op.

The silicification of these rhyalite dikes occurred in conjunction with the mineralization of the Las Pilas Diorite and the La Pimienta Metasediments Barr, op. The Las Pilas Diorite has undergone extreme alteration.

In order to better illustrate the textural and mineralogical characteristics of the metamorphic rocks, the detailed petrology of a representative phyllite and marble is presented below.

Datación Radioquímica by Dave Von Hohenheim on Prezi

Almost all the phyIlites examined in thin section possess one direction of foliation, as evidenced by the parallel alignment of micaceous minerals.

Metamorphic Rocks There is noticeable variation in the major chemistry of the metamorphic rock samples. In as much as these rocks are of low metamorphic grade, the observed variation is considered to be principally the result of differences in original composition. The objective of this study is to attempt to unravel the geologic history of the region in the light of new geological, petrological, and geochemical data.


Porphyritic diorite is present but rare. The late Paleozoic age assigned to the lowermost La Pimienta phyllite by Burckhardt op. Member ii, with a thickness of only 25 mm, is the least extensive of the members in Unit B.

At most exposures, however, the marble appears massive and unfolded. The thickness of these layers ranges from 1 to 4 cm. Quartz and sericite are present in about equal proportions and constitute 90 percent of the rock with accesory epidote 1 percentalkali feldspar 5 to 7 percentand opaque minerals 2 to 4 percent.

Is a homogeneous, mediurn-dark-gray N4slaty phyllite. An enlarged map of the major arroyos shows the structural detail at a scale of 1;2, Figure 2. 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, The abundance of phyllite fragments readily differentiates this metaconglomerate from that found in Dafacion B. These two belts, the Jaliscoan on the west and the Huastecan on the east, were sites of Paleozoic geosynclinal sedimentation.

The only sedimentary rock exposed in the region is a red conglomerate composed chiefiy of metamorphic and dioritic rock fragments.

The lowermost metamorphic unit, which is exposed in Arroyo del Alamo, is designated Unit A.