Petrogenesis of Lavas along the Solomon Island Arc, SW Pacific: Coupling of Compositional Variations and Subduction Zone Geometry
Petrogenesis of Lavas along the Solomon Island Arc, SW Pacific: Coupling of Compositional Variations and Subduction Zone Geometry
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DOI：
10.1093/petrology/egp019
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发表时间：
2009-05
影响因子：
3.9
通讯作者：
S. Schuth;C. Münker;S. König;C. Qopoto;S. Basi;D. Garbe‐Schönberg;C. Ballhaus
中科院分区：
文献类型：
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作者：
S. Schuth;C. Münker;S. König;C. Qopoto;S. Basi;D. Garbe‐Schönberg;C. Ballhaus
西南太平洋的所罗门岛弧对了解俯冲带火山活动特别有意义，因为岛弧活动部分的岩浆活动主要由镁铁质熔体控制，从而可以直接了解地幔过程。沿着所罗门岛弧，印度-澳大利亚板块目前正在向太平洋板块之下俯冲。至少在C。1200万年前，太平洋板块俯冲到印度-澳大利亚板块之下，直到白垩纪Ontong Java高原与北方岛弧碰撞。1000公里）。玄武岩和安山岩是最丰富的岩石类型。苦橄岩和铁榴石产于所罗门群岛的新格鲁吉亚群，在那里它们在俯冲Woodlark扩张中心上方喷发，也产于瓦努阿图北部的圣克鲁斯群岛，在那里伦内尔断裂带正在俯冲。最近的工作还确定了埃达克岩（Sr/Yup至c）的存在。200）和高镁安山岩（MgO 45 wt %，Sr/Y c. [11^46]）。大多数的高镁安山岩的埃达克岩的遗传联系，但一些高镁安山岩表现出亲和力玻安岩组成。大离子亲石元素丰度在大多数所罗门岛弧岩浆表明一个强大的源叠加俯冲成分。Sr/Sr和eNd值沿着弧分别为0.7029 ~ 0.7052和0.508 ~ 0.808 3。测得的eHf值范围从100 - 105到140 - 146。如果校正俯冲成分的贡献，结合eHf^eNd系统学也表明，大多数研究的所罗门弧熔岩产生的印度型地幔域。然而，少数样品显示eHf^eNd组成类似于太平洋型地幔域。这些样品要么来自古老的太平洋基底（玄武岩），要么来自俯冲的太平洋地壳（埃达克岩）。铅同位素组成受俯冲成分控制，可用于确定两种不同类型的俯冲成分的存在，它们起源于（1）太平洋板块，包括翁东爪哇高原物质（4600万年前）和（2）最近俯冲的印度-澳大利亚板块。结合Hf、Nd、Pb同位素数据还表明，翁东爪哇高原的下部进入地幔楔，如以前的地球物理模型所假设的。
The Solomon island arc, SW Pacific, is of particular interest for understanding subduction zone volcanism, as magmatism in the active part of the arc is dominated by mafic melts, thus permitting direct insights into mantle processes. Along the Solomon island arc, the Indian^Australian plate is subducting at present beneath the Pacific plate. However, until at least c. 12 Myr ago, the Pacific plate was subducting beneath the Indian^Australian plate until the Cretaceous Ontong Java Plateau collided with the northern Solomon island arc.To evaluate the effects of the changes in tectonic regime on lava compositions, we present a comprehensive Sr^Nd^ Hf^Pb isotope, major element and trace element dataset, covering lavas erupted along the entire island arc (c. 1000 km). Basalts and andesites represent the most abundant rock types. Picrites and ankaramites occur in the New Georgia Group of the Solomon Islands, where they erupted above the subductingWoodlark spreading center, and also in the Santa Cruz archipelago, north of Vanuatu, where the Rennell Fracture Zone is subducting. Recent work has also identified the presence of adakites (Sr/Yup to c. 200), and high-Mg andesites (MgO45 wt %, Sr/Y c. 11^46). Most of the high-Mg andesites are genetically linked to the adakites, but some of the high-Mg andesites show affinities to boninitic compositions. Large ion lithophile element abundances in most Solomon island arc magmas indicate a strong source overprint by subduction components. Sr/Sr and eNd values along the arc range from 0 7029 to 0 7052 and from þ5 8 to þ8 3, respectively.The Sr^Nd values partially overlap the compositions of oceanic basalts from the Indian^Australian plate. Measured eHf values range from þ10 5 to þ14 6. If corrected for contributions from subduction components, combined eHf^eNd systematics also indicate that most of the studied Solomon arc lavas were generated within the Indian-type mantle domain. However, a few samples display eHf^eNd compositions resembling those of the Pacific-type mantle domain. These samples either originate from older Pacific basement (basalts) or represent melts derived from subducted Pacific crust (adakites). Lead isotope compositions, controlled by subduction components, can be used to identify the presence of two distinct types of subduction components that originate (1) from the Pacific plate including Ontong Java Plateau material (46 Myr old) and (2) from the more recently subducted Indian^ Australian plate. Combined Hf^Nd^Pb isotope data also reveal that lower parts of the Ontong Java Plateau entered the mantle wedge, as previously postulated by geophysical models.