Petrogenesis of Rinjani Post-1257-Caldera-Forming-Eruption Lava Flows

Abstract

-After the catastrophic 1257 caldera-forming eruption, a new chapter of Old Rinjani volcanic activity began with the appearance of Rombongan and Barujari Volcanoes within the caldera. However, no published petrogenetic study focuses mainly on these products. The Rombongan eruption in 1944 and Barujari eruptions in pre-1944, 1966, 1994, 2004, and 2009 produced basaltic andesite pyroclastic materials and lava flows. A total of thirty-one samples were analyzed, including six samples for each period of eruption except from 2004 (only one sample). The samples were used for petrography, whole-rock geochemistry, and trace and rare earth element analyses. The Rombongan and Barujari lavas are composed of calc-alkaline and high K calc-alkaline porphyritic basaltic andesite. The magma shows narrow variation of SiO 2 content that implies small changes during its generation. The magma that formed Rombongan and Barujari lavas is island-arc alkaline basalt. Generally, data show that the rocks are enriched in Large Ion Lithophile Elements (LILE: K, Rb, Ba, Sr, and Ba) and depleted in High Field Strength Elements (HFSE: Y, Ti, and Nb) which are typically a suite from a subduction zone. The pattern shows a medium enrichment in Light REE and relatively depleted in Heavy REE. The processes are dominantly controlled by fractional crystallization and magma mixing. All of the Barujari and Rombongan lavas would have been produced by the same source of magma with little variation in composition caused by host rock filter process. New flux of magma would likely have occurred from pre-1944 until 2009 period that indicates slightly decrease and increase of SiO 2 content. The Rombongan and Barujari lava generations show an arc magma differentiation trend.

Determination of the seismicity and peak ground acceleration for Lombok island: an evaluation on tectonic setting

“…The south subduction tends to produce deep earthquakes; whereas the north back-arc thrust tends to produce shallow earthquakes (Fig. 8).The Benioff zone may develop at depths of 150 km, similar to the so-called Benioff-Wadati zone by Rachmat et al [2]. The zone may be inclined with an angle of 67 0 downward north (Fig.…”

“…The island is tectonically located in the west of the Sunda Arc where the Australian Continental Plate subducts beneath the Eurasian Plate [1,2], (Fig. 1).…”

Species and potential sources of phosphorus in groundwater in and around Mataram City, Lombok Island, Indonesia

“…3is the dissolution of minerals (e.g., apatite) that may contain P in some phases [21,30,31]. Volcanic rocks and deposits contain P [32,33], as does lava on Lombok Island; for the latter, the levels of P detected were reported as percentages of P 2 O 5 ranging from 0.15 to 0.47 [34] and 0.19 to 0.27 [35]. The presence of apatite was also reported [35].…”

Grouting performance of the Pandan Duri dam shacked by Lombok earthquake 2018

“…When water filled the reservoir, it had an elevation of +281.5 m at a normal water supply level (FSL). The volume of reservoir was 27.2x106 m 3 . Putting all those data into load calculations, shear forces on the dam base was 415679.5 kg/m 2 .…”