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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Late Quaternary tephra in the New Ireland Basin, Papua New Guinea
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Late Quaternary tephra in the New Ireland Basin, Papua New Guinea

机译：巴布亚新几内亚新爱尔兰盆地晚第四纪特弗拉

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Sediment cores were recovered from the New Ireland Basin, east of Papua New Guinea, in order to investigate the late Quaternary eruptive history of the Tabar-Lihir-Tanga-Feni (TLTF) volcanic chain. Foraminifera δ~(18)O profiles were matched to the low-latitude oxygen isotope record to date the cores, which extend back to the early part of δ~(18)O Stage 9 (333 ka). Sedimentation rates decrease from > 10 cm/1000 yr in cores near New Ireland to ～ 2 cm/ 1000 yr further offshore. The cores contain 36 discrete ash beds, mostly 1-8 cm thick and interpreted as either fallout or distal turbidite deposits. Most beds have compositionally homogeneous glass shard populations, indicating that they represent single volcanic events. Shards from all ash beds have the subduction-related pattern of strong enrichment in the large-ion lithophile elements relative to MORB, but three distinct compositional groups are apparent: Group A beds are shoshonitic and characterised by > 1300 ppm Sr, high Ce/Yb and high Nb/Yb relative to MORB, Group B beds form a high-K series with MORB-like Nb/Yb but high Ce/Yb and well-developed negative Eu anomalies, whereas Group C beds are transitional between the low-K and medium-K series and characterised by flat chondrite-normalised REE patterns with low Nb/Yb relative to MORB. A comparison with published data from the TLTF chain, the New Britain volcanic arc and backarc including Rabaul, and Bagana on Bougainville demonstrates that only Group A beds share the distinctive phenocryst assemblage and shoshonitic geochemistry of the TLTF lavas. The crystal- and lithic-rich character of the Group A beds point to a nearby source, and their high Sr, Ce/Yb and Nb/ Yb match those of Tanga and Feni lavas. A youthful stratocone on the eastern side of Babase Island in the Feni group is the most probable source. Group A beds younger than 20 ka are more fractionated than the older Group A beds, and record the progressive development of a shallow level magma chamber beneath the cone. In contrast, Group B beds represent glass-rich fallout from voluminous eruptions at Rabaul, whereas Group C beds represent distal glass-rich fallout from elsewhere along the volcanic front of the New Britain arc.
机译：从巴布亚新几内亚东部的新爱尔兰盆地回收了沉积岩心，以研究塔巴尔-利希尔-坦加-费尼（TLTF）火山链的第四纪晚期喷发历史。有孔虫的δ〜（18）O剖面与低纬度氧同位素记录相吻合，迄今的岩心年代可以追溯到δ〜（18）O阶段9的早期（333 ka）。沉积速率从新爱尔兰附近的岩心中的> 10 cm / 1000 yr降低到更远的海底处的〜2 cm / 1000 yr。岩心包含36个离散的灰烬床，大多数为1-8厘米厚，被解释为沉降物或远端的浊质沉积物。大多数床具有组成上均质的玻璃碎片种群，表明它们代表了单个火山事件。相对于MORB，所有灰分床中的碎片均具有与俯冲相关的强离子亲石元素富集模式，但明显存在三个不同的组成组：A组床为粗晶型，特征在于Sr> 1300 ppm，高Ce / Yb和相对于MORB较高的Nb / Yb，B组床形成了高K系列，具有MORB样的Nb / Yb，但Ce / Yb较高，且Eu负异常发育良好，而C组床在低K和高K之间过渡中等K系列，其特征是相对于MORB具有较低Nb / Yb的扁平球粒陨石归一化REE模式。与TLTF链，新英国的火山弧和后弧（包括Rabaul）和Bougainville上的Bagana的已发布数据进行比较，结果表明，只有A组床具有TLTF熔岩的独特的表晶组合和肖氏体地球化学。 A组床的富含晶体和石块的特征指向附近的来源，其高Sr，Ce / Yb和Nb / Yb与Tanga和Feni熔岩的高。最有可能的来源是费尼群中巴巴斯岛东侧的一个年轻的层状锥。小于20 ka的A组床比较旧的A组床更易碎，并记录了圆锥下方浅层岩浆室的逐渐发展。相比之下，B组岩床代表了Rabaul大量火山喷发带来的富含玻璃的沉淀，而C组岩床代表了来自新不列颠弧沿线其他地方的远端富含玻璃的沉淀。

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