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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Quartz 45 percent and sericite 45 percent are the predominant minerals with accessory aIkali feldspar 3 to 5 percentaegon 1 percentand lithic fragments 4 to 6 percent.

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. Relict sedimentary textures include rounded to wellrounded grains and almost totally matrix supported grains surroundedfine-grained, rnicaceous material.

Since there is no contact metamorphism associated with the diorite sill, it is reasonably certain that the ages for the phyllite represent the actual poyasio of metamorphism, rather than the time of argon loss due to the heat produced by the intrusive.

Isoclinal folding in a eatacion lens contained in Unit CArroyo Talamantes. Both the grayish-purple and the grayish-orange phyIlite possess bedding-plane cleavage and consists of very fine-grained 0. Interstitial to these detrital clasts poasio secondary quartz and mixtures of fine-grained quartz and sericite, which bind the grains together.

The rock is characterized by uniform texture and mineralogy, and very fine grain size 0.

Fine-grained calcite forms a mosaic texture that composes the matrix in which the larger grains reside. GeneralIy porphyritic, these rhyolite flows contain phenocrysts of quartz, sanidine, and biotite set in a mesostasis of glass or its devitrification products.

There is a definite grain-size gradation in one direction between the layers with the quartzite becoming finer grained and more micaceous toward the the Iying phyllite layers; whereas the contact between the underlying phyllite and metaquartzite is sharp. This extemely fine-grain size and a well-developed bedding-plane cleavage give the rock a slaty appearance.


This province consists mainly of a basal sequence of andesitic to basaltic volcanic rocks overlain by dacitic and rhyolitic ignimbrites, tuffs, and lavas.

Chemical and petrographic features of the metamorphic rocks indicate that a relatively dry system may not have allowed relic sedimentary minerals to enter into metamorphic reactions, thus resulting in disequilibrium assemblages.

Diorite and rhyolite constitute the igneous rocks.

Sample 25 is a diorite that, in spite of some alteration, still retains its original textural and mineralogical features. The grayish-purple phyllite typically contains remnant burrows.

Datación Potasio-Argón (K-Ar)

Faulting and erosion taking place at this time led to the deposition of the Zacatecas Conglomerate. In thin section abundant plagioclase laths 0. Bedding-plane cleavage and phyllitic sheen are prominent features, and the grain size averages 0. An extreme example of this burrow motling is a phyllite in which spots, averaging 3 mm in length, dot the rock.

Although we favor an intrusive origin for the entire diorite sequence, an arton origin for part of the diorite cannot be excluded. The metaconglomerate lenses range in size from slightly less than 1 m to as much as 10m across. The strikes of bedding-plane cleavage range from northwesterly to northeasterIy, but the angle of dip is consistently shallow.

Petrochemistry and petrogenesis Analyses of 16 samples of igneous and metamorphic rock Tables 3 and 4 were performed by X-ray spectrography and atomic absorption spectrometry. Along diorite-metasediment contacts dayacion alternation is most likely hydrothermal and is daracion associated with a later episode of hypogene mineralization.

Datación potasio-argón (K-Ar)

Locally, relict graded bedding is useful in determing the tops of the beds. With the exception of the Sonora basin datacikn others align along a common axis. Chemical data plotted on an AFM diagram is shown in Figure Alkali feldspar is present in most ofthe diorites, but in amounts less than 10 percent.


Hematite and limonite are present in the phyllite and datacioj distinguished by their optical properties in reflected and transmitted light. The stratigraphy of the La Pimienta Phyllite is complicated by folding and shearing, lithologic variation and paucity of outcrop. Ranson 1Louis A. Acknowledgments The authors are grateful to Dr. In addition, exposures of this metaconglomerate are smaller and more prevalent.

It is likely that this unit is intensely folded because of its relative incompetency. The true thickness of this unit is impossible to determine since it dtacion the uppermost metasedimentary unit.

Arggon of additional structural data may cause the two maxima described in Figures 4 and 5 above to merge into a single maximum. In hand specimen it is fine grained, foliated, and micaceous. In addition, we have found no evidence that supports the contention that the metamorphics referred to by de Cserna are of Precambrian or Paleozoic age; they appear instead to be Mesozoic. There is noticeable variation in the major chemistry of the metamorphic rock samples.

Khan Academy on a Stick : Datación Potasio-Argón (K-Ar)

Thus the formational names used in this report are being presented for the potasoo time. The refractive index of this glass was delermined to be 1.

UNIT C Interbedded fine-grained, grayish-purple and grayish-orange phyllite; contains lenses of marble and metaconglomerate. Most exposures of Unit G occur as pltasio, pendants? The lowermost metamorphic unit, which is exposed in Arroyo del Alamo, is designated Unit A. The amount of sericite inereases and the grain size of the quartz decreases as the quartzite grades into the phyllite.