Palaeomagnetic determination of emplacement temperature of Vesuvius AD 79 pyroclastic deposits

Abstract

accurate in each data system to better than 1 s during the period of the measurements. The time during which the cable measurements were made was relatively quiet geomagneticallyB. Five of the most quiet days were selected to represent the Sq variation measured at Green Hill. These days, and their daily sum global geomagnetic activity indices 'i.Kp were: 3 May,-6; 4 May,-9; 5 May,-14; 17 May, +5; 18 May,-8. The averages ofthese five quiet days in the three magnetic field components measured at Green Hill are shown as solid lines in Fig. 2. These averages are obtained from the hourly mean values. The time dependences during a day show typical Sq patterns for this geomagnetic latitude, except for the local morning intervals in the Hand Z-components. The dashed lines in Fig. 2 show the computed Sq curves expected on the basis of the spherical harmonic analysis of the potential for the daily variation by Chapman and Bartels 9 • We used the harmonic coefficients of Matsushita lO for location B on the model cable path in Fig. 1. The fit of the calculated Sq patterns using location B is quite good in the east-west component but is not good for the local morning observations in either the north-south or the vertical components. In addition, the magnitude of the Sq variation observed in the local afternoon in the north-south component is about a factor of two larger than that predicted by the model Sq calculations. These disagreements in the north-south and vertical components are

Italian zeolitized rocks of technological interest

“…This type of zeolite and its chemical composition are both definitely related to the original glass belonging to the high-potassium series, whereas its genesis is ascribed to the interaction of the glass with hot fluids. The emplacement temperature of these flows ranges between 35ff and 100 ~'C (Kent et al 1981).…”

Applications of paleomagnetism in the volcanic field: A case study of the Unzen Volcano, Japan

“…Remanence of pyroclastic deposits is often contaminated by secondary components of viscous origin (viscous remanent magnetization; VRM) or chemical origin (chemical remanent magnetization; CRM). Hence, studies of T E of pyroclastic flows need to involve careful analysis of the progressive thermal demagnetization (Kent et al, 1981). In the case of hemoilmenite-bearing pumice fall, Copy right c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRA-PUB.…”

The use of palaeomagnetism and rock magnetism to understand volcanic processes: introduction

“…These workers assumed that the NRM consisted of essentially the TRM and therefore, in the absence of progressive thermal demagnetization data, they could not provide information bearing on whether any of the deposits came to rest at an intermediate temperature. Nonetheless, their research provided the basis for subsequent workers to further develop methods of estimating emplacement temperatures based on progressive thermal demagnetization characteristics of clasts in the rocks, improving the method's accuracy and precision even as instruments improved (Chadwick 1971;Hoblitt & Kellogg 1979;Kent et al 1981;Urrutia-Fucugauchi 1983;McClelland & Druitt 1989;Tamura et al 1991;Pares et al 1993;Mandeville et al 1994;Bardot & McClelland 2000;Cioni et al 2004;Zanella et al 2007). Today, a common practice is to sample lithic fragments that were entrained in the pyroclastic current and use detailed, progressive thermal demagnetization methods to extract the full character of the NRM in the clasts and, from these data, infer temperatures of emplacement.…”