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首页> 外文期刊>Contributions to Mineralogy and Petrology >Concentric zoning in the Tunk Lake pluton, coastal Maine
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Concentric zoning in the Tunk Lake pluton, coastal Maine

机译：缅因州沿海Tunk湖岩体的同心分区

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The Tunk Lake pluton of coastal Maine, USA is a concentrically zoned granitic body that grades from an outer hypersolvus granite into subsolvus rapakivi granite, and then into subsolvus non-rapakivi granite, with gradational contacts between these zones. The pluton is partially surrounded by a zone of basaltic and gabbroic enclaves, interpreted as quenched magmatic droplets and mushes, respectively, as well as gabbroic xenoliths, all hosted by high-silica granite. The granite is zoned in terms of mineral assemblage, mineral composition, zircon crystallization temperature, and major and trace element concentration, from the present-day rim (interpreted as being closer to the base of the chamber) to the core (interpreted as being closer to the upper portions of the chamber). The ferromagnesian mineral assemblage systematically changes from augite and hornblende with augite cores in the outermost hypersolvus granite to hornblende, to hornblende and biotite, and finally, to biotite only in the subsolvus granite core of the pluton. Sparse fine-grained basaltic enclaves that are most common in the outermost zone of the pluton suggest that basaltic magma was present in the lower portions of the magma chamber at the same time that the upper portions of the magma chamber were occupied by a granitic crystal mush. However, the slight variations in initial Nd isotopic ratio in granites from different zones of the pluton suggest that contamination of the granitic melt by basaltic melt played little role in generating the compositional gradation of the pluton. The zone of basaltic and gabbroic chilled magmatic enclaves, and gabbroic xenoliths, hosted by high-silica granite, that partially surround the pluton is interpreted as mafic layers at the base of the pluton that were disrupted by invading late-stage high-silica magma. These mafic layers are likely to have consisted of basaltic lava layers and basalt that chilled against granitic magma to produce coarse-grained gabbroic mush. Basaltic and gabbroic magmatic enclaves and gabbroic xenoliths are hornblende-bearing, suggesting that their parent melts were relatively hydrous. The water-rich nature of the underplating mafic magmas may have prevented extensive invasion of the granitic magma by these magmas, owing to the much greater viscosity of the granitic magma than the mafic magmas in the temperature range over which magma interaction could have occurred.
机译：美国缅因州沿海的Tunk Lake岩体是一个同心带状的花岗岩体，从外超溶质花岗岩逐渐变质为非溶质雷帕基维花岗岩，然后变为非溶质非雷帕基维花岗岩，这些区域之间具有渐变接触。岩体部分地被玄武岩和辉长岩飞地包围，分别被解释为急冷的岩浆飞沫和麝香，以及辉长岩异岩，均由高硅质花岗岩构成。从矿物组成，矿物组成，锆石结晶温度以及主要和微量元素浓度的角度，花岗岩从当今的边缘（被解释为更靠近腔室的底部）到岩心（被解释为更接近的区域）划分。到腔室的上部）。亚铁镁矿物的组合系统地从最外层超溶花岗岩中的闪长岩和角闪闪岩芯转变成角闪石，再到角闪闪岩和黑云母，最后变成仅在岩体的亚溶质花岗岩芯的黑云母。在岩体最外部最常见的稀疏细粒玄武岩飞地表明，在岩浆室下部存在玄武岩浆的同时，岩浆室的上部被花岗岩晶体糊状物占据。 。但是，来自不同岩体区域的花岗岩中初始Nd同位素比率的细微变化表明，玄武质熔体对花岗岩熔体的污染在产生岩体的组分级配中几乎没有作用。由高硅花岗岩构成的玄武岩和辉长岩岩浆飞地以及辉长岩异岩体部分包围着岩体，这被解释为岩体底部的镁铁质层，由于侵入晚期高矽质岩浆而被破坏。这些镁铁质层可能由玄武岩熔岩层和玄武岩组成，这些玄武岩层与花岗岩岩浆一起冷却，产生粗粒辉长岩糊状物。玄武岩和辉长岩岩浆飞地和辉长岩异岩都带有角闪石，表明它们的母体熔体相对含水。由于在可能发生岩浆相互作用的温度范围内，花岗岩岩浆的黏度比镁铁质岩浆高得多，所以底层镁铁质岩浆的富水性质可能阻止了这些岩浆对花岗岩岩浆的广泛入侵。

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