On the Recycling of Amphibole-rich Ultramafic Intrusive Rocks in the Arc Crust: Evidence from Shikanoshima Island (Kyushu, Japan)
On the Recycling of Amphibole-rich Ultramafic Intrusive Rocks in the Arc Crust: Evidence from Shikanoshima Island (Kyushu, Japan)
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DOI：
10.1093/petrology/egs016
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发表时间：
2012-06
影响因子：
3.9
通讯作者：
M. Tiepolo;A. Langone;T. Morishita;M. Yuhara
中科院分区：
文献类型：
--
作者：
M. Tiepolo;A. Langone;T. Morishita;M. Yuhara
日本九州鹿之岛白垩纪富含角闪石的镁铁质岩和相关花岗岩的矿物化学和U^Pb年代学为角闪石在弧岩浆岩石成因中的作用提供了新的见解。在鹿之岛的东北部，在花岗闪长岩的寄主岩中发现了长约600米的富角闪石基性岩石。基性岩体的核部由富角闪石辉长闪长岩组成，具有斑状结构。向寄主花岗闪长岩方向，斑状结构逐渐消失，出现了一条相对均匀的中-细粒-富含角闪石的斑状辉长辉长岩由大的角闪石颗粒（体积分数高达60%）组成，其特征是具有棕色核，偶见单斜辉石包裹体和绿色边缘。这些大的角闪石颗粒分散在由绿色角闪石、单斜辉石和斜长石组成的细粒基质中。有关志贺之岛镁铁质岩的全岩资料表明，它们是高镁安山岩（HMA）的侵入对应物。主要和微量元素矿物组成揭示了显着的棕色角闪石（及其包裹体）和基质矿物之间的化学对比，这表明他们不是在同一个液体下降线。棕色角闪石及其单斜辉石包裹体继承自富含角闪石的超镁铁质侵入地壳岩石（如角闪石岩），其结晶自化学成分接近大陆弧玄武岩的熔体。U^Pb年代学数据表明，捕虏晶物质的年龄比基质矿物大约早2000万年。基质矿物结晶从类似于sanukite型HMA的母液，并具有微量元素特征，其特征在于具有高地壳亲和力的元素的强烈富集和重稀土元素的耗尽。绿色角闪石是一种常见的矿物，在所有的岩性研究，这使我们能够监测的成分变化的液体，它结晶移动从核心的镁铁质杂岩的主机granodiantes.The数据显示，间隙熔体相互作用的熔体富含元素具有高的地壳亲和力，在该领域的密切联系，被推断为主机花岗岩类。这些结果有利于sanukite型HMA的起源，而不是从原始地幔熔体，但从地幔熔体已受到地壳过程的影响，并已被地壳物质污染。主要和微量元素组成的棕色角闪石从志贺之岛镁铁质岩的棕色角闪石相比，从其他富含角闪岩侵入岩在全球范围内的造山环境（阿尔卑斯山链和罗斯造山带）。所观察到的相似性表明，富含角闪石的镁铁质岩是一个共同的地球化学亲和力，是独立的年龄和当地的地球动力学背景，从而涉及到一个特定的成岩过程的岩浆过程的表达。富含角闪石的镁铁质和超镁铁质侵入岩可能是所有碰撞系统的共同特征，因此代表了一个“隐藏”的角闪石水库在弧cruster.We显示，角闪石在岩石成因的sanukite型HMA中发挥了重要作用，但也预计将发挥重要作用，在许多其他弧岩浆的分化。
New insights into the role of amphibole in arc magma petrogenesis are provided by the mineral chemistry and U^Pb geochronology of Cretaceous amphibole-rich mafic rocks and associated granitoids from Shikanoshima Island (Kyushu, Japan). In the northeastern part of Shikanoshima Island a relatively large body (about 600 m in length) of amphibole-rich mafic rocks is found within granodiorite host-rocks.The core of the mafic body consists of amphibole-rich gabbrodiorite with a porphyritic texture.Towards the host granodiorite the porphyritic texture is progressively lost and a band of relatively homogeneous mediumto fine-grained mafic rock marks the boundary with the granitoid rocks.The amphibole-rich porphyritic gabbrodiorite consists of large amphibole grains (up to 60 vol. %) characterized by brown cores, occasional inclusions of clinopyroxene, and green rims. These large amphibole grains are dispersed in a fine-grained matrix consisting of green amphibole, clinopyroxene and plagioclase. Literature whole-rock data on the mafic rocks from Shikanoshima Island suggest that they are the intrusive counterparts of high-Mg andesite (HMA). Major and trace element mineral compositions reveal a marked chemical contrast between the brown amphibole (and its inclusions) and the matrix minerals, suggesting that they are not on the same liquid line of descent. The brown amphibole and its clinopyroxene inclusions were inherited from amphibole-rich ultramafic intrusive crustal rocks (e.g. hornblendites) crystallized from a melt with a chemical composition close to that of continental arc basalts. U^Pb geochronological data suggest that the xenocrystic material is about 20 Myr older than the matrix minerals. The matrix mineral crystallized from a parental liquid similar to sanukite-type HMA and with a trace element signature characterized by strong enrichment in elements with high crustal affinity and depletion in heavy rare earth elements. Green amphibole is a common mineral in all the studied lithologies; this allowed us to monitor the compositional variations in the liquid from which it crystallized moving from the core of the mafic complex to the host granodiorite.The data reveal that the interstitial melt had interacted with a melt enriched in elements with a high crustal affinity that, given the close association in the field, is inferred to be the host granitoid. These results favour an origin for sanukite-type HMA not from primary mantle melts but from mantle melts that have been affected by crustal processes and have been contaminated by crustal material. The major and trace element composition of the brown amphibole from the Shikanoshima Island mafic rocks is compared with that of brown amphibole from other amphibolite-rich intrusive rocks in orogenic settings worldwide (Alpine chain and Ross Orogen). The observed similarities suggest that the amphibole-rich mafic rocks are the expression of a magmatic process with a common geochemical affinity that is independent of the age and local geodynamic setting and thus related to a specific petrogenetic process. Amphibole-rich mafic and ultramafic intrusive rocks could be a common feature of all collisional systems and thus represent a ‘hidden’amphibole reservoir in the arc crust.We show that amphibole plays a major role in the petrogenesis of sanukite-type HMA but is also expected to play a major role in the differentiation of many other arc magmas.