New geochemical data are presented from prehistoric and historical eruptive products of the Lamongan volcanic field (LVF), East Java; a region of the Sunda arc covering ∼260 km2 and containing ∼90 eruptive vents plus the historically active Lamongan volcano. LVF lavas include medium-K basalts and basaltic andesites from historical eruptions of Lamongan and prehistoric eruptions in the eastern LVF, along with a high-K suite represented by prehistoric deposits in the western LVF. Although lacking some of the characteristics of truly primary basalts, the least evolved lavas identified in the LVF have some of the lowest SiO2 contents (∼43 wt % SiO2) yet reported in Sunda arc volcanic rocks. Mass balance considerations indicate that two chemically distinct LVF magmas may be parental to suites currently being erupted from the neighbouring volcanoes, Semeru and Bromo. Lamongan’s historical lavas can be related to the medium-K andesitic products of Semeru by fractional crystallization, despite the former’s location at the same distance from the trench as Bromo, a high-K volcano. Extensional tectonics, possibly related to arc segmentation in the region of the LVF, creating conditions that promote the rapid ascent of parental magmas, is probably responsible for this and several other features of the complex.
东爪哇拉蒙干火山田 (LVF) 的史前和历史喷发产物提供了新的地球
化学数据;巽他弧的一个区域,面积约 260 平方公里,包含约 90 个喷发孔以及历史上活跃的拉蒙干火山。 LVF 熔岩包括来自 Lamongan 历史喷发和 LVF 东部史前喷发的中 K 玄武岩和玄武质安山岩,以及以 LVF 西部史前沉积物为代表的高 K 套件。尽管缺乏真正的原生玄武岩的一些特征,但在 LVF 中发现的最不演化的熔岩具有一些最低的 SiO2 含量(~43 wt% SiO2),这是迄今为止在巽他岛弧火山岩中报道的。质量平衡考虑表明,两种
化学性质不同的 LVF 岩浆可能是目前从邻近的塞梅鲁火山和布罗莫火山喷发的岩浆的母体。拉蒙甘的历史熔岩可以通过分步结晶与塞梅鲁的中
钾安山岩产物联系起来,尽管前者与高
钾火山布罗莫距离海沟的距离相同。伸展构造可能与 LVF 区域的弧分段有关,创造了促进母体岩浆快速上升的条件,这可能是造成该杂岩体的这一特征和其他几个特征的原因。