Volcanological and petrological evolution of Barren Island (Andaman Sea, Indian Ocean)

Contexto geológico e litogeoquímica das unidades plutônicas-vulcânicas da região de União do Norte, setor leste da Província Aurífera de Alta Floresta (MT)

“…Rafael Rodrigues de Assis et al fonte mantélica, a exemplo daquelas originadas em arcos vulcânicos (Chandrasekharam et al 2009, Wernick 2004, Yang et al 2008.…”

Major ash eruptions of Barren Island volcano (Andaman Sea) during the past 72 kyr: clues from a sediment core record

“…Absence of an identifiable ash layer younger than 10 ka is well in accord with the hypothesis that the caldera of BI formed as a result of a single, simple, symmetric collapse along circular (ring) faults (Sheth et al 2009), and was not associated with a major eruption as speculated by Shanker et al (2001). Unlike ε Nd values, 87 Sr/ 86 Sr ratios of ash layers in the core overlap with each other, and with that of the ash and lavas on BI (Table 1; Luhr and Haldar 2006;Chandrasekharam et al 2009), and therefore are of little use as stratigraphic markers. Also, data from a single core may not be sufficient to reconstruct the complete eruption history of BI volcano, since it is quite possible that many of the past ash eruptions of the volcano were simply not recorded at our core site because of their dispersal in other directions.…”

“…Data sources: Ash layer in the core, ash deposits on BI, and lavas on Narcondam: this work; BI lavas: Luhr and Haldar (2006); Chandrasekharam et al (2009); lavas and ash from volcanoes of Indonesia: Turner and Foden (2001) during this large time period. The first marked change in magma composition is observed in the~15 ka eruption, and since then the composition has been variable as is apparent from the variable ε Nd of historic and recent eruptions on BI (Table 1; Luhr and Haldar 2006;Chandrasekharam et al 2009). The highest ε Nd value measured for ash layers of the core is 6.7, a composition shown only by the lavas and ash deposits of BI that are exposed in the caldera wall of the volcano, and which thus predate the caldera itself.…”

“…The highest ε Nd value measured for ash layers of the core is 6.7, a composition shown only by the lavas and ash deposits of BI that are exposed in the caldera wall of the volcano, and which thus predate the caldera itself. In comparison, all historic and modern (caldera-filling) eruptions of the volcano have produced lava and ash with much lower ε Nd values (~5.0 or less) (Table 1; Luhr and Haldar 2006;Chandrasekharam et al 2009). This relationship may be an indication that the caldera of BI volcano is younger than~10 ka, the age of the youngest ash layer in the core with the ε Nd value of 6.7.…”

“…Trace element abundances of these rocks are typical of subduction zone magmas and the Sr-Nd-Pb isotopic ratios reflect derivation from a large-ion-lithophile element (LILE)-poor mantle. The 87 Sr/ 86 Sr ratios of BI samples vary between 0.70381-0.70413 (with respect to a value of 0.71025 for NBS987 standard), whereas ε Nd values vary from +4.3 to +7.4 (with respect to a value of −15.2 for La Jolla standard) (Luhr and Haldar 2006;Chandrasekharam et al 2009). There are no differences in isotopic compositions among basalt, basaltic andesite and andesite samples observed in the existing limited database.…”