Vol52,2,2009 197 ANNALS OF GEOPHYSICS, VOL. 52, N. 2, April 2009 Key words petrophysics - thermal and magnetic properties - radioactive heat production - volcanic rocks 1. Introduction The Mt Melbourne Volcanic Field, forming the youngest volcanic system of the McMurdo Volcanic Group, is located in the Victoria Land (Antarctica) at the eastern flank of the Ross Sea rift. The latter is part of the West Antarctic Rift System, one of the largest tectonic provinces of the Earth with extended continental crust (e.g. Storti et al., 2008). Volcanic evidence shows that rifting commenced after the break-up of Australia and Antarctica about 100 Ma and was active until the middle Cenozoic (Cande et al., 2000; Hamilton et al., 2001). General overviews of volcanological, stratigraphical and other field aspects as well as geochemical information on individual volcanic fields of the McMurdo Vol- canic Group are given by Kyle (1990) and Wörner (1999), whereas Armienti et al. (1991) and Rocholl et al. (1995) focus on rocks from the Mt Melbourne Volcanic Field (figs. 1 and 2). This work falls within a program of geo- physical research aimed at studying the supply system and zones of accumulation of magma in the crust of the McMurdo Volcanic Group. We present the results of petrophysical properties useful to calibrate models of crustal structure. We carried out laboratory measure- ments of thermal and magnetic properties of lavas of the Mt Melbourne Volcanic Field. These properties were determined in connec- tion with bulk density and porosity. A set of Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica) Vincenzo Pasquale, Massimo Verdoya, Paolo Chiozzi and Egidio Armadillo Dipartimento per lo Studio del Territorio e delle sue Risorse, Settore di Geofisica, Università di Genova, Italy Abstract We present the results of measurements of physical properties carried out on mafic lavas from the Mt Melbourne Volcanic Field, useful for interpretation of geophysical surveys designed to shed light on the structure of the crust. The thermal conductivity is comparable to that of glass and shows a clear negative dependence on poros- ity. The volume heat capacity and the thermal diffusivity are less variable. The concentration of the thermally important natural radioactive isotopes was determined by gamma-ray spectrometry. Lavas denoted a rather low heat-production rate, and the largest concentration of heat-producing elements (potassium, uranium, thorium) was found in the trachyte samples. The magnetic susceptibility is more variable than the other physical proper- ties and, among the several iron-titanium oxides, it appears primarily controlled by the ulvöspinel-magnetite sol- id solution series. Mailing address: Prof. Vincenzo Pasquale, Diparti- mento per lo Studio del Territorio e delle sue Risorse, Set- tore di Geofisica, Università di Genova, Via Benedetto XV 5, I-16132 Genova, Italy; e-mail:pasquale@dipteris.unige.it Vol52,2,2009 17-06-2009 19:02 Pagina 197 198 V. Pasquale, M. Verdoya, P. Chiozzi and E. Armadillo Fig. 1. Sketch map of the Mt Melbourne Volcanic Field showing position of sampling sites (see table I for sam- ple codes and types of rocks). Sub-fields: WCG – West of Campbell Glacier, SN – Shield Nunatak, OR – Oscar Ridge, WR – Washington Ridge, EP – Edmonson Point, BR – Baker Rocks, RH – Random Hills, MM – Mt Mel- bourne summit. gamma-ray spectrometry measurements were also carried out to determine the concentrations of uranium, thorium and potassium and the ra- dioactive heat-production rate of the different rock types. 2. Sampling and laboratory procedure Figure 1 shows the location of the sampling sites and the main sub-fields of the Mt Mel- bourne Volcanic Field. The presence of an ice Vol52,2,2009 17-06-2009 19:02 Pagina 198 199 Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica) sheet allowed sampling of the exposed volcanic rocks only in Washington Ridge, Edmonson Point, Baker Rocks, Shield Nunatak and Mt Melbourne summit sub-fields. As a whole, twenty samples were collected paying attention to avoid sampling of rocks with evident weath- ering. Table I presents the chemical composi- tion for each sample obtained by means of in- ductively coupled plasma mass spectrometry at the Activation Laboratories LTD, Ontario (Canada), whereas fig. 3 depicts the alkali-sili- ca diagram and the rock classification. The Washington Ridge (WR) is formed by a line of sub-aerial scoria cones and tuff rings. All samples of lavas are characterized by the lack of feldspar phenocrysts and, with the ex- ception of sample WR6, they have a chemical composition ranging from basanite to amphi- bole-bearing tephrite. In the Edmonson Point (EP) eruptive centres and scattered deposits of tuff-breccias and pillows show a complex asso- ciation of different rock types; our lava samples range from tephritic to trachyandesitic compo- sition. The Shield Nunatak (SN) area is formed by a cluster of subglacial eruptive centres with a flat-topped morphology; we recovered only one sample of basaltic composition. Lithotypes sampled at Baker Rock (BR) range from basan- ites (BR1-BR3) to trachybasalt (BR4). The Mt Melbourne summit (MM) is a stratovolcano formed between 0.01-0.25 Ma, built on a base of trachytic lava flows and domes; samples are of trachyandesitic-trachytic to basaltic compo- sition. Thermal and magnetic properties of rock of the Mt Melbourne Volcanic Field were investi- gated according to standard procedures imple- mented at our laboratory. The thermal conduc- tivity, thermal diffusivity and volume heat ca- pacity measurements were carried out at room temperature by two devices: (i) an apparatus (PRC) devised by us (Pasquale, 1982 and 1983); (ii) a heat transfer analyzer (ISOMET) for measurements under transient regime, man- ufactured by Applied Precision Ltd. (Bratisla- va, Slovakia). The heat-production rate and the magnetic susceptibility were obtained from measurements with a gamma-ray spectrometer (GRS) and a magnetic susceptibility system (MS2) manufactured by EG & G-Ortec (Usa) and Bartington Instruments (Witney, Oxford, England), respectively. The PRC apparatus allows accurate deter- minations of thermal conductivity of solid ma- terial in the range 0.3−11 W m-1 K-1. The total relative uncertainty, as shown by experiments Fig. 2. Schematic cross-section of the lithosphere showing the transition from the Ross Sea rift to the Transantarctic Mountains, based on geophysical data, xenolith evidence and information from volcanic rocks (Wörner, 1999). 1. Sediments, 2. Upper crust, 3. Lower crust, 4. Mt Melbourne Volcanic Field. Vol52,2,2009 17-06-2009 19:02 Pagina 199 200 V. Pasquale, M. Verdoya, P. Chiozzi and E. Armadillo performed on materials with well-known ther- mal properties, is less than 3%. Reproducibility of measurements on various rock samples is within ± 2%. PRC requires the sample to be prepared in cylindrical shape and clamped be- tween two cylindrical copper blocks by a screw. The whole apparatus is initially kept at the same temperature, then the lower block is cooled and the temperature of the blocks is con- tinuously recorded with thermocouples. When a uniform temperature gradient is established within the stack of elements, the thermal con- ductivity of the sample is determined, the heat capacity of the upper block of copper and of the sample being known. ISOMET uses a dynamic measurement method which allows simultaneous determina- tions of conductivity, diffusivity and volume heat capacity. The measurement range is 0.02− 6 W m-1K-1 for conductivity and 0.04−4 106 J Table I. Chemical composition (in mass %) obtained from inductively coupled plasma mass spectrometry (ICP-MS) and rock type (see fig. 1 for sample location). Sample SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 S Total Rock type WR1 43.65 3.27 13.51 3.99 9.31 0.21 7.96 8.67 4.35 1.66 1.04 0.08 97.70 Basanite WR2 42.29 3.98 12.68 4.29 10.11 0.18 8.43 10.48 3.75 1.95 0.83 0.73 99.70 Basanite WR3 45.05 3.31 14.06 3.00 9.50 0.21 7.32 8.41 4.54 2.08 1.16 0.03 98.67 Basanite WR4 45.62 2.72 14.42 3.50 11.08 0.24 3.96 8.02 4.30 1.77 1.79 0.04 97.46 Basanite WR5 44.92 3.64 14.20 3.96 8.79 0.20 7.42 8.87 4.66 2.22 0.83 0.06 99.77 Basanite WR6 46.68 2.55 15.37 3.38 9.08 0.21 5.67 9.08 4.24 1.47 0.97 0.02 98.72 Trachybasalt WR7 42.30 3.77 15.22 4.36 10.00 0.21 5.30 9.21 3.36 1.07 1.15 0.06 96.01 Basanite EP1 50.40 2.04 16.64 3.03 9.09 0.25 2.79 6.72 5.34 2.32 1.01 0.05 99.68 Basaltic trachyandesite EP2 44.62 4.11 15.71 4.09 10.01 0.22 4.84 10.04 3.70 1.15 1.21 0.11 99.81 Tephrite EP3 58.83 0.99 16.37 3.11 6.05 0.23 0.89 3.70 5.80 3.70 0.31 0.02 99.80 Trachyandesite EP4 48.34 2.57 16.52 3.36 9.09 0.23 3.64 8.10 4.61 1.89 1.21 0.06 99.62 Trachybasalt EP5 48.67 2.68 15.52 4.09 9.10 0.25 3.46 7.72 4.53 2.14 1.34 0.03 99.53 Trachybasalt EP6 46.65 2.87 15.29 3.08 9.56 0.21 6.46 9.66 4.02 1.50 0.97 0.02 99.89 Trachybasalt SN1 45.07 2.95 12.67 2.80 9.92 0.18 10.55 11.78 2.56 0.66 0.69 0.09 99.92 Basalt BR1 42.45 2.04 13.40 2.82 7.25 0.19 6.89 8.16 4.57 1.82 0.93 0.05 90.57 Basanite BR2 43.39 3.42 16.45 4.26 8.91 0.19 6.13 10.81 3.08 1.04 0.98 0.06 98.72 Basanite BR3 44.73 3.33 13.63 4.83 8.31 0.18 10.12 9.34 3.36 1.14 0.59 0.03 99.59 Basanite BR4 48.57 2.75 14.82 2.86 11.36 0.26 3.44 7.77 4.50 1.95 1.49 0.03 99.80 Trachybasalt MM1 61.18 0.30 16.66 2.51 3.77 0.21 0.11 1.29 6.35 5.58 0.11 0.03 98.10 Trachyte MM2 47.02 3.96 19.76 2.82 7.62 0.14 2.04 6.66 2.98 1.06 1.01 0.04 95.11 Basalt Vol52,2,2009 17-06-2009 19:02 Pagina 200 201 Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica) m-3K-1 for volume heat capacity, while repro- ducibility is 3% for both parameters, and the experimental relative error is less than 5%. Sample preparation for the ISOMET procedure is fast and only requires the rock to be cut and smoothed to obtain a flat surface. Interchange- able probes, calibrated for different ranges of thermal conductivity, are directly put on the sample surface. Thermal parameters are in- ferred from the increase in temperature with time at the sample surface due to heat flow re- leased by a planar heat source. The GRS consists of a scintillation detector (a 7.62 cm × 7.62 cm NaI(Tl) crystal with reso- lution about 7%) and a 2048 channel analyser. The counting time for each sample was 5400 s. Based on counting statistics, the relative stan- dard uncertainty on U, Th and K determinations are, in percent, 3.5, 2.4 and 1.2, respectively. For ultrabasic rocks with exceptionally low ra- dioelement concentration the error may in- crease to 20%. For a sample weighing 0.750 kg, the detection limits are 0.1 ppm for U, 0.2 ppm for Th, and 0.02% for K (Chiozzi et al., 2000a). The MS2 system measures the magnetic susceptibility on samples (cores or powders) of 15 ml. It can be used for investigations of mag- netic mineralogy and grain size and for deter- mination of the Curie transition temperature. The relative uncertainty in the determinations is Fig. 3. Total alkali content (Na2O + K2O) vs. SiO2. Numbers at each data point correspond to those listed in table I. ol = olivine and q = quartz. Vol52,2,2009 17-06-2009 19:02 Pagina 201 202 V. Pasquale, M. Verdoya, P. Chiozzi and E. Armadillo as low as 5%, and the sensitivity is 2 10-6 SI. Repeated measurements on standards revealed very low drift. The system has a low operating frequency, so that measurements are not affected by sam- ple conductivity. Compact rock samples were first cut with diamond disk to obtain flat surfaces as required by thermal property determinations according to the ISOMET procedure. The surface dimen- sions were at least 6 cm in diameter and the minimum thickness 2-3 cm. Samples were then cored with a head-diamond corer. The core specimens, about 3 cm high and 2.5 cm in diameter, were used for the determi- nations with PRC and MS2. Less massive rocks which could not be cut were reduced to powder. This allowed both measurements of magnetic Table II. Bulk density (ρ), porosity (σ), thermal conductivity (λ1 by ISOMET, λ2 by PRC), volumetric heat ca- pacity (ρ×c) and thermal diffusivity (k). ρ ϕ λ1 Std. λ2 Std. ρ×c Std. k Std. Sample (kg m-3) (%) (W m-1K-1) Dev. (W m-1K-1) Dev. (J m-3K-1) Dev. (m2 s-1) Dev. ×106 ×10-6 WR1 2520 18 - - 1.08 0.18 - - - - WR2 1440 55 0.53 0.02 0.60 0.09 1.61 0.02 0.33 0.01 WR3 2160 24 0.92 0.05 0.94 0.08 1.85 0.02 0.49 0.03 WR4 2240 23 0.84 0.01 - - 1.82 0.01 0.46 0.01 WR5 2480 15 1.00 0.02 - - 1.89 0.02 0.53 0.01 WR6 2470 17 0.86 0.01 - - 1.89 0.02 0.46 0.01 WR7 2890 1 - - 1.23 0.26 - - - - EP1 2740 9 1.04 0.01 - 1.94 0.02 0.54 0.01 EP2 2730 10 1.23 0.02 1.14 0.09 2.02 0.01 0.61 0.01 EP3 2370 13 0.82 0.01 - - 1.88 0.01 0.33 0.01 EP4 2440 6 1.03 0.02 - - 1.91 0.01 0.54 0.01 EP5 2750 1 1.02 0.02 - - 1.71 0.02 0.60 0.01 EP6 2870 2 - - - - - - - - SN1 3030 1 1.38 0.06 - - 1.94 0.04 0.71 0.02 BR1 2000 12 - - 0.97 0.15 - - - - BR2 2660 12 1.19 0.06 - - 1.89 0.09 0.63 0.01 BR3 2770 10 0.99 0.03 - - 1.73 0.03 0.57 0.01 BR4 2300 23 0.98 0.06 0.91 0.09 1.85 0.10 0.53 0.01 MM1 1740 34 0.55 0.01 0.48 0.16 1.81 0.05 0.30 0.01 MM2 2700 7 - - 1.06 0.34 - - - - Vol52,2,2009 17-06-2009 19:02 Pagina 202 203 Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica) susceptibility and GRS analyses to determine the concentration of heat-producing isotopes. A volume of 500 cm3, corresponding to rock mass ranging from 0.650 to 0.850 kg, was adopted for spectrometric measurements. Moreover, bulk density and porosity were determined for all the samples. Thermal, GRS and magnetic measurements were carried out on five specimens obtained from each rock sample. 3. Results and discussion Table II summarises the results of bulk den- sity, porosity and thermal parameters. Thermal conductivity varied from 0.48 W m-1K-1 (tra- chyte MM1) to 1.38 W m-1K-1 (basalt SN1). For the five samples investigated with both PRC and ISOMET, the results are quite coherent, as the maximum difference between the two methods is close to the instrumental error (0.1 W m-1K-1). Table III. Concentration of the heat-producing elements (U, Th, K), radioactive heat-production rate (RHP) and magnetic susceptibility (χ). Sample K Std. U Std. Th Std. RHP Std. χ(SI units) Std. (%) Dev. (ppm) Dev. (ppm) Dev. (µW m-3) Dev. ×10-5 Dev. WR1 1.54 0.04 2.2 0.1 8.8 0.4 1.23 0.06 4486 11 WR2 1.68 0.04 1.4 0.2 5.7 0.5 0.49 0.07 231 1 WR3 1.97 0.04 3.0 0.1 12.0 0.5 1.43 0.06 3622 5 WR4 1.56 0.04 1.2 0.2 5.3 0.4 0.68 0.07 898 18 WR5 1.92 0.04 2.5 0.1 10.0 0.5 1.39 0.07 4057 3 WR6 0.85 0.04 0.6 0.2 6.5 0.4 0.63 0.04 2096 2 WR7 0.78 0.03 0.7 0.2 2.7 0.3 0.47 0.07 494 4 EP1 2.00 0.04 2.2 0.2 8.2 0.5 1.34 0.07 1904 4 EP2 1.00 0.03 1.1 0.2 3.9 0.4 0.65 0.06 338 5 EP3 3.27 0.05 3.2 0.1 11.9 0.5 1.71 0.07 822 1 EP4 1.02 0.04 0.9 0.2 3.2 0.4 0.50 0.06 879 17 EP5 1.77 0.04 1.6 0.1 6.1 0.4 1.02 0.06 1764 6 EP6 1.30 0.04 1.5 0.2 4.8 0.4 0.89 0.07 1805 3 SN1 0.67 0.03 0.8 0.2 2.1 0.4 0.46 0.06 298 1 BR1 1.42 0.05 0.6 0.3 3.3 0.6 0.38 0.08 791 3 BR2 0.89 0.03 0.8 0.2 3.1 0.4 0.50 0.07 813 1 BR3 0.99 0.03 0.9 0.2 3.6 0.4 0.59 0.07 4617 2 BR4 1.66 0.04 1.7 0.1 7.4 0.5 0.94 0.06 2243 9 MM1 4.53 0.08 5.3 0.2 19.0 0.8 2.00 0.08 119 1 MM2 1.05 0.04 1.6 0.2 7.6 0.5 1.04 0.07 648 1 Vol52,2,2009 17-06-2009 19:02 Pagina 203 204 V. Pasquale, M. Verdoya, P. Chiozzi and E. Armadillo On the average, the volumetric heat capacity and the diffusivity are 1.85 (± 0.10) 106 J m-3 K-1 and 0.51 (± 0.12) 10-6 m2 s-1, respectively. Since the chemical composition is relatively homoge- neous, thermal conductivity is mainly con- trolled by porosity. Figure 4 clearly points out a linear decrease of this parameter with the in- crease in porosity, whose maximum value (55%) was found for WR2 (basanite). The radioactive elements that mostly con- tribute to the internal heat generation are urani- um, thorium and potassium. These elements Fig. 4. Thermal conductivity values versus porosity. Fig. 5. Relative contribution of U, Th and K to the radioactive heat-production rate. Vol52,2,2009 17-06-2009 19:02 Pagina 204 205 Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica) were determined by the three window method. Details on the adopted procedure and the sys- tem calibration are given by Chiozzi et al. (1998; 2000a and 2000b). In general, this method involves the detection of the gamma-ra- diation emission in the decay of 214Bi (238U se- ries), 208Tl (232Th series), and 40K. However, it must be stressed that secular radioactive equi- librium in the decay series is necessary for ap- propriate measurements. This condition is gen- erally fulfilled in 40K and 232Th series while problems may arise for uranium, where a mini- mum age of 0.3 My is required for 226Ra equi- librium. The age of some volcanic sub-fields of Mt Melbourne is as young as 0.25 My. This means that secular equilibrium between U and its de- cay products might not be fulfilled in all the rock sampled. To bypass this problem, the gam- ma-ray spectrum region comprised between 0.03 and 0.10 MeV was investigated, instead of the higher energy photo-peak of 214Bi (1.76 MeV) (Ketcham, 1996). Chiozzi et al. (2000b) tested this approach on volcanic rocks younger than 0.3 My by comparing results from the NaI(Tl) spectrometer with a semiconductor (HPGe) detector, and they found that use of the low energy window can remarkably reduce the uncertainty in the U determination. In this low- energy region, there are a number of gamma rays produced by the decay of 234Th. This ra- dioelement can be safely assumed to be in sec- ular equilibrium with 238U as its half-life is only 24.1 days, and therefore it could have a differ- ent activity from post-226Ra daughter products, like 214Bi. As the NaI(Tl) scintillation detector does not have sufficient resolution for reliable identification of individual peaks in this region of low energy, it was necessary to operate with a relatively wide window, ranging from 0.010 to 0.123 MeV. The results of GRS analyses are shown in table III. Generally, lava samples denoted rather low radioelement concentrations. The largest concentration of heat producing elements (K, U and Th) was found in the trachytic sample MM1 (4.53%, 5.3 ppm and 19.0 ppm, respec- tively), whereas SN1 (basalt) resulted in the poorest in K and Th (0.67% and 2.1 ppm, re- spectively). The lowest concentrations of U (0.6 ppm) were obtained for BR1 (basanite) and WR6 (trachybasalt). If one neglects WR6, the Th/U ratio is 3.93 ± 0.59, i.e. not significantly different from the average value found in the literature. If the rock density is known, the radioactive heat-production rate RHP due to the decay of 235U, 238U, 232Th and 40K can be calculated from the uranium and thorium concentrations (see Chiozzi et al., 2002 for details). Considering the relative standard uncertainties and the de- tection limits of the GRS determinations, the resulting error on RHP is 0.1 µW m-3. The ma- jor effect is due to U, whereas the accuracy and the detection limit of K are almost negligible in this regard. The radiogenic heat productivity of the ana- lyzed lavas is relatively low, as a consequence of the low concentration of heat-producing radioele- ments (table III). RHP ranges from a minimum of 0.38 µW m-3 for BR1 (basanite) to a maximum of 2.00 for MM1 (trachyte). The relative contribu- tion supplied by U, Th and K to the radioactive heat-production rate is shown in fig. 5. The results of magnetic susceptibility meas- urements are also shown in table III. Measured values, which range from 0.001 (trachyte MM1) to 0.046 SI units (basanite BR3), mainly depend on the content of iron-titanium oxides. The ox- ides of interest in rock magnetism form a terna- ry system with FeO, Fe2O3 and TiO2 as the end- members (fig. 6). The most interesting minerals in this system are wüstite (Fe1-xO), magnetite (Fe3O4), hematite (α-Fe2O3), maghemite (γ- Fe2O3), pseudobrookite (Fe2TiO5), ferropseudo- brookite (FeTi2O5), ilmenite (FeTiO3), and ul- vöspinel (Fe2TiO4). There are three fundamental solid-solution series in this system: the ul- vöspinel-magnetite series with an inverse spinel structure, the rhombohedral hematite-ilmenite series, and the orthorhombic pseudobrookite- ferropseudobrookite series (Petersen, 1976; Hunt et al., 1995). Figure 6 shows the iron-tita- nium oxides for the examined lavas together with the major solid-solution series. The lava magnetic components are clustered round the ulvöspinel-magnetite solid solution series [xFe2TiO4(1 - x)Fe3O4] of x-value ranging from 0.5 to 0.7, as the most abundant mineral compo- nent responsible for the magnetic susceptibility. Vol52,2,2009 18-06-2009 15:56 Pagina 205 206 V. Pasquale, M. Verdoya, P. Chiozzi and E. Armadillo Many titanomagnetites are slightly oxidized to- wards the titanohematite line or reduced. 4. Conclusions We identified the thermal and magnetic properties, together with density and porosity, of some mafic lavas representative of the Mt Melbourne Volcanic Field. This information is of basic importance for interpretation of gravi- ty and magnetic anomalies, and is essential for future studies on the thermal structure of the area. Thermophysical properties reflect the ef- fects of various geological processes acting during and after lava formation. The thermal conductivity of lavas is compa- rable to that of glass and diminishes till it halves with the increase in porosity. Gamma- ray spectrometry results show low concentra- tions of radioactive elements and thus a low ra- dioactive heat-production rate. For almost all the lava samples analyzed, the thorium/uranium ratio indicates no process of post-magmatic al- teration. Titanomagnetites appear to be the most abundant mineral components responsible for magnetic susceptibility. Fig. 6. Composition of the titanomagnetites of the investigated lavas. Vol52,2,2009 17-06-2009 19:02 Pagina 206 207 Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica) Acknowledgements The authors thank Giorgio Caneva for his field work and support in laboratory measure- ments. REFERENCES ARMIENTI, P., L. CIVETTA, F. INNOCENTI, P. MANETTI, A. TRIPODO, L. VILLARI and G. VITA (1991): New petro- logical and geochemical data on Mt. Melbourne Vol- canic Field (northern Victoria Land, Antarctica): II. Italian Antarctic Expedition, Mem. Soc. Geol. It., 46, 397-424. CANDE, S.C., J.M. STOCK, R.D. MULLER and T. ISHIHARA (2000): Cenozoic motion between East and West Antarctica, Nature, 404, 145-150. CHIOZZI P., V. PASQUALE and M. VERDOYA (1998): Ground radiometric survey of U, Th and K in the Lipari Island, Italy, J. Appl. Geophys., 38, 209-217. CHIOZZI P., P. DE FELICE, V. PASQUALE and M. 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