scholarly journals PRELIMINARY PALAEOMAGNETIC STUDY OF LOWER TERTIARY VOLCANIC ROCKS FROM MORELOS AND GUERRERO STATES

1983 ◽  
Vol 22 (1) ◽  
pp. 87-110
Author(s):  
J. Urrutia-Fucugauchi
Keyword(s):  
Volcanic Rocks ◽  
Lower Tertiary

Resultados de un estudio paleomanético preliminar de siente unidades volcánicas del Terciario Temprano, expuestas en los estados de Morelos y Guerrero, aparentemente no concuerdan con datos similares del norte de México. Las unidades estudiadas son dos lavas de la Formación Balsas (Paleoceno-Eoceno), dos tobas de la Riolita Tilzapotla (edad K-Ar de 49 ± 3 m.a.) y dos tobas y una lava andesítica del Mioceno (?). Los resultados paleomagnéticos, suponiendo que representan el campo magnético ambiental al tiempo del emplazamiento de las unidades, podrían ser explicados en términos de rotaciones tectónicas de las áreas estudiadas en sentido contrario a las manecillas del reloj. Dichas rotaciones estarían asociadas con compresión regional a lo largo de un sistema de fallas laterales izquierdas, aparentemente siguiendo la traza del eje volcánico mexicano. Los resultados son considerados insuficientes para una interpretación tectónicas y se requiere de más datos paleomagnéticos para apoyar la posibilidad de rotaciones tectónicas en el área.

scholarly journals Fission track dating of lower Tertiary rhyolitic glass rocks from Disko

1985 ◽  
Vol 125 ◽  
pp. 28-30
Author(s):  
K Hansen ◽  
A.K Pedersen
Keyword(s):  
Late Stage ◽  
Fission Track ◽  
Volcanic Rocks ◽  
Time Span ◽  
Fission Track Dating ◽  
West Greenland ◽  
Lower Tertiary ◽  
Igneous Activity ◽  
Geomagnetic Anomaly ◽  
Age Determinations

The Tertiary igneous activity in West Greenland has not been dated in detail. Sediments contemporaneous with, or slightly older than, the early volcanic rocks are assigned amiddle Paleocene age from palaeontological evidence (Henderson et al., 1981), and palaeomagnetic work by Athavale & Sharma (1975) indicates that the Vaigat Formation picrites and the lower 500 m or so of the overlying Maligât Formation (Hald & Pedersen, 1975) were erupted in the time span represented by geomagnetic anomaly 25 together with the long reversal period between anomalies 25 and 24. The age estimated for this period is 56 to 52 Ma (Butler & Coney, 1981). The late Stage lamprophyre magmatism on Ubekendt Ejland appears to be much younger, about 30 to 40 Ma (Parrott & Reynolds, 1975). No reliable radiometric age determinations have been published from the Disko-Nûgssuaq area.

Sur la presence de galets de laves rhyolitiques dans les conglomerats du delta miocene de Voreppe (Isere)

1966 ◽  
Vol S7-VIII (2) ◽  
pp. 281-284 ◽  
Author(s):  
Jacqueline Bocquet ◽  
Robert Michel
Keyword(s):  
Volcanic Rocks ◽  
Western Alps ◽  
Magmatic Evolution ◽  
Alpine Orogeny ◽  
Lower Tertiary ◽  
Important Link

Abstract The Miocene of the Grenoble region (France) is composed almost entirely of conglomerates of deltaic origin. Among the pebbles are volcanic rocks of a rhyolitic nature, which have been studied microscopically and chemically. These rhyolitic pebbles may be the remains of a lower Tertiary volcanic episode with a center located in the ultra-Dauphinois flysch zone, now obliterated by erosion. For the western Alps, lower Tertiary volcanism would be considered an important link in the magmatic evolution connected with the Alpine orogeny.

Lower Tertiary volcanic rocks off Kristiansund — Mid Norway

1980 ◽  
Vol 35 (4) ◽  
pp. 277-286 ◽  
Author(s):  
Tom Bugge ◽  
Tore Prestvik ◽  
Kåre Rokoengen
Keyword(s):  
Volcanic Rocks ◽  
Lower Tertiary

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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