Search

Your search keyword '"Alva ‐ Valdivia, L. M."' showing total 35 results
Start Over Author "Alva ‐ Valdivia, L. M."
35 results on '"Alva ‐ Valdivia, L. M."'

1. Curie Temperatures and Emplacement Conditions of Pyroclastic Deposits From Popocatépetl Volcano, Mexico

Author

Dudzisz, K., Kontny, A., Alva‐Valdivia, L. M., and 3 Universidad Nacional Autónoma de México (UNAM) Instituto de Geofísica Laboratorio de Paleomagnetismo Ciudad Universitaria Ciudad de México Mexico

Subjects
magnetic mineralogy studies, Popocatépetl volcano, pyroclastic deposits, ddc:552.2, magnetic rock studies, cooling temerature
Abstract

Most pyroclastic deposits of Popocatépetl volcano were emplaced at high temperatures and have similar mafic to more evolved compositions, suggesting a long‐lived, interconnected magma environment. We performed a magnetic and microscopic study on different eruptive sequences, Plain Language Summary: Explosive eruptions of volcanoes are a dangerous threat to human settlements. In this study, we investigated pyroclastic material from the last 14 ky of Popocatépetl volcano using magnetic mineral assemblages, hysteresis properties, and temperature‐ and field‐dependent magnetic susceptibility. The data are suited to separate different eruption phases and provide information on the volcanic material history and emplacement conditions. Magnetic susceptibility analyses are suggested to be a complementary tool to the paleomagnetic directional analysis for the determination of emplacement temperatures., Key Points: Several Curie temperatures were observed in pyroclastic deposits. Temperature and field dependence of magnetic susceptibility are suited to separate eruption phases. Irreversible Curie temperatures in heating and cooling curves observed in block‐and‐ash flows may suggest rapid quenching., DGAPA‐UNAM, https://doi.org/10.17632/9g2tszftvr.2, https://earthref.org/MagIC/19591/206809c5-acfc-41e3-b4cb-411630a7025e

Published
2022

14. Paleomagnetism and tectonics from the late Pliocene to late Pleistocene in the Xalapa monogenetic volcanic field, Veracruz, Mexico.

Author

Alva-Valdivia, L. M., Agarwal, A., García-Amador, B., Morales-Barrera, W., Agarwal, K. K., Rodríguez, S., and Gonzalez-Rangel, J. A.

Subjects
*VOLCANIC fields, *PALEOMAGNETISM, *MAGNETIC domain, *MICROSCOPY, *VOLCANOLOGY, *MINERALOGY
Abstract

The Xalapa monogenetic volcanic field, Veracruz, Mexico is located at the eastern end of the Trans-Mexican Volcanic Belt. This study uses specimens from 0.8 ka to 5.96 ± 0.156 Ma Xalapa lava deposits and from 4.5 ± 0.028 Ma La Concha ignimbrite. The study identifies the magnetic mineralogy by reflected light microscopy, thermomagnetic curves, and coercivity estimates. It further defines the magnetic domain size distribution by hysteresis plots, Day diagrams, and first-order-reversal-curves. Characteristic remanent directions and virtual geomagnetic poles are also calculated. The characteristic remanent directions are used to establish the magnetostratigraphy and to identify the net rotation experienced, at each site, since the emplacement. The results allow the identification of the rotation domains, and R'-, P-, and Y-shears, active since the past ~2.5 m.y. in the region and a better characterization of the displacement along the Río Actopan fault, active in the Xalapa monogenetic volcanic field. [ABSTRACT FROM AUTHOR]

Published
2019
Full Text
View/download PDF

15. Alternating augite-plagioclase wedges in basement dolerites of Lockne impact structure, Sweden: A new shock wave-induced deformation feature.

Author

Agarwal, A., Reznik, B., Alva ‐ Valdivia, L. M., and Srivastava, D. C.

Subjects
PLAGIOCLASE, AUGITE, DIABASE, STRUCTURAL geology, SHOCK waves, ROCK deformation
Abstract

This paper reports peculiar alternating augite-plagioclase wedges in basement dolerites of Lockne impact structure, Sweden. The combined microscopic and spectroscopic studies of the micro/nanoscale wedges reveal that these are deformation-induced features. First, samples showing wedges, 12 out of 18 studied, are distributed in the impact structure within a radius of up to 10 km from the crater center. Second, the margins between the augite and labradorite wedges are sharp and the {110} prismatic cleavage of augite develops into fractures and thereafter into wedges. The fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain. Third, compared to the bulk labradorite, the dislocation density and the residual strain in the labradorite wedges are significantly higher. A possible mechanism of genesis of the wedges is proposed. The mechanism explains that passing of the shock waves in the basement dolerite induced (i) formation of microfractures in augite and labradorite; (ii) development of the augite prismatic cleavages into the wedges, which overprint the microfracture in the labradorite wedges; and (iii) thereafter, infilling of microfractures in the augite wedges by labradorite. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

34. ESTUDIOS DE PROCEDENCIA DE MATERIALES ARQUEOLOGICOS MEDIANTE MICROSCOPIA ELECTRONICA DE BARRIDO.

Author

Angeles-García, S., Reyes-Salas, A. M., Alva-Valdivia, L. M., de Leon, A. Cisneros, and Ortega-Gutiérrez, F.

Abstract

Mexico has two main sources of ilmenite, in the Oaxaca and Chiapas states. Ilmenite is an oxide composed by iron and titanium generally accompanied with apatite. About six tons of small cubic rocks mainly composed of ilmenite were found in San Lorenzo Tenochtitlan (Veracruz state), where Olmec culture flourished. This rock type was the object of study. Samples were observed by an electron scanning microscopy (JEOL JSM- 6300 and microsonde JEOL JXA 8300R) and WDS analyses, which contributed to determine that, by comparison, the most probable source of these samples is Huitzo Precambrian rocks in Oaxaca state. [ABSTRACT FROM AUTHOR]

Published
2014

Catalog

Books, media, physical & digital resources
See catalog results