Origin of Late Paleogene to Neogene basalts and associated coeval felsic volcanic rocks in Southwest Hokkaido, northern NE Japan arc: Constraints from Sr and Nd isotopes and major- and trace-element chemistry
Origin of Late Paleogene to Neogene basalts and associated coeval felsic volcanic rocks in Southwest Hokkaido, northern NE Japan arc: Constraints from Sr and Nd isotopes and major- and trace-element chemistry
复制标题
DOI：
10.1016/j.lithos.2011.02.020
复制
发表时间：
2011-07
期刊：
影响因子：
3.5
通讯作者：
K. Takanashi;K. Shuto;M. Sato
中科院分区：
文献类型：
--
作者：
K. Takanashi;K. Shuto;M. Sato
北海道西南部、日本东北弧北部发现的玄武岩和长英质火山岩（主要是英安岩和流纹岩）是渐新世（34-30Ma）、早中新世（25-17Ma）、中中新世（16-12Ma）、晚中新世（10-5Ma）、上新世（4Ma）和第四纪 (2Ma)，从而跨越了日本海开口前到开口后阶段。与一些中新世早期玄武岩相比，大约 16Ma 后的大多数玄武岩显示出贫 Sr (SrI) 和 Nd (NdI) 同位素特征，这在时间和范围上与日本东北部中部弧后玄武岩的 SrI 和 NdI 值的变化非常相似弧。然而，较年轻的玄武岩存在显着差异，从中中新世开始，在北海道西南部的东部、过渡带和西部火山带中发现了具有贫化 SrI 和 NdI 特征的玄武岩，而在日本东北弧中部，具有相似同位素特征的玄武岩仅限于弧后侧。 北海道西南部的长英质火山岩具有 SrI 和 NdI 特征。 NdI 值，与同时代的北海道西南部玄武岩重叠。尽管镁铁质和长英质岩石之间的关系可归因于分步结晶，但该过程与稀土元素化学不一致，因为总稀土元素不会从玄武岩到长英质火山岩系统地增加。另外，下地壳基性岩，以 Itinome-gata（男鹿半岛）玄武岩中发现的辉长岩和角闪岩捕虏体为代表，是晚古近纪至第四纪长英质岩浆的可能来源，因为长英质火山岩和捕虏体都具有相似的 SrI 和 NdI。北海道西南部的火山岩始于渐新世（34Ma），软流圈地幔上涌，随后部分熔融，生成贫化 SrI 和 NdI 的玄武岩岩浆（松江玄武岩），随后软流圈衍生的玄武岩岩浆与上覆的次大陆岩石圈相互作用。在早中新世（25-17 Ma），软流圈上涌引发了上覆岩石圈地幔的部分熔融，大多数具有未贫化 SrI 和 NdI 值的玄武岩均源自该岩石圈地幔。在中新世（16-12 Ma）期间，由于日本海的开放，上覆岩石圈变薄，导致软流圈上升流到达现在日本东北部弧火山锋下方的区域。软流圈的部分融化导致整个北海道西南部产生大量的玄武岩浆，其 SrI 和 NdI 值已耗尽。大多数自晚中新世以来喷发的玄武岩也被认为是由软流圈地幔形成的。渐新世以来形成的玄武岩岩浆要么喷发，要么熔化并加热下地壳，从而产生了同时代的长英质岩浆。
Basalts and felsic volcanic rocks (mainly dacite and rhyolite) found in southwest Hokkaido, northern part of the NE Japan arc, result from protracted volcanism during the Oligocene (34–30 Ma), Early Miocene (25–17 Ma), Middle Miocene (16–12 Ma), Late Miocene (10–5 Ma), Pliocene (4 Ma) and Quaternary (2 Ma), thus spanning the pre-Japan Sea opening to post-opening stages.The majority of basaltic rocks after about 16 Ma show depleted Sr (SrI) and Nd (NdI) isotopic signatures compared with some Middle to Early Miocene basalts, which strongly resemble, in terms of both timing and extent, the change in SrI and NdI values for back-arc basaltic rocks of the central NE Japan arc. However, significant differences exist for younger basaltic rocks, in that basaltic rocks with depleted SrI and NdI signatures are found from the Middle Miocene onwards throughout the eastern-, transitional- and western-volcanic zones in SW Hokkaido, whereas in the central NE Japan arc, basaltic rocks with similar isotopic signatures are confined to the back-arc side.Felsic volcanic rocks in southwest Hokkaido have SrI and NdI values, which overlap with coeval southwest Hokkaido basaltic rocks. Although the relationship between mafic and felsic rocks could be attributed to fractional crystallization, this process is inconsistent with REE chemistry, as total REE do not increase systematically from basaltic rocks to felsic volcanic rocks. Alternatively, lower crustal mafic rocks, represented by gabbroic and amphibolitic xenoliths found in basaltic rocks at Itinome-gata (Oga Peninsula), are a possible source for Late Paleogene to Quaternary felsic magmas, as both felsic volcanic rocks and xenoliths have similar SrI and NdI.A possible tectono-magmatic model for the production of post-Late Paleogene volcanic rocks from SW Hokkaido commences in the Oligocene (34 Ma) with asthenospheric mantle upwelling followed by partial melting to generate basalt magma (Matsue basalt) with depleted SrI and NdI, followed by interaction of asthenosphere-derived basalt magmas with overlying subcontinental lithosphere. In the Early Miocene (25–17 Ma), asthenospheric upwelling triggered partial melting of the overlying lithospheric mantle from which most basalts with undepleted SrI and NdI values were derived. During the Middle Miocene (16–12 Ma), thinning of the overlying lithosphere due to the opening of the Japan Sea resulted in asthenospheric upwelling which reached the region beneath the present NE Japan arc volcanic front. Partial melting of the asthenosphere led to generation of voluminous basalt magma with depleted SrI and NdI values throughout southwest Hokkaido. Most basaltic rocks that erupted since the Late Miocene are considered to have also formed from asthenospheric mantle. Basaltic magmas formed since the Oligocene have either been erupted, or fluxed and heated the lower crust from which coeval felsic magmas were generated.