Andesites erupted from Tongariro volcano, North Island, New Zealand contain feldspathic and quartzose xenoliths derived from basement rocks. New major oxide, trace element and Sr-Nd-Pb isotopic data indicate that both the Waipapa and Kaweka (meta)sedimentary terranes are represented in erupted xenoliths, rather than only the Kaweka terrane as previously thought. Xenolith mineral assemblages differ from their likely source materials, notably through the lack of white mica, illite, chlorite and quartz, which is reflected in contrasting chemical and isotopic compositions. Major and trace element data indicate that most xenoliths underwent bulk mass decreases of about 50% when pyrometamorphosed at temperatures of ~800–980 °C, similar to typical Tongariro magma temperatures of ~800–1000 °C. Bulk Eu concentrations were retained (in restitic plagioclase); however, other rare earth elements are commonly lower in xenoliths than in protoliths. In xenoliths, the Nd/Nd ratios of protoliths were also retained, which indicates that xenoliths were derived from the Kaweka and Waipapa terranes in subequal amounts. Reductions in Sr/Sr ratios by up to 0.003 in xenoliths, relative to their likely protoliths, were accompanied by decreases in Rb/Sr ratios from 0.1–0.8 down to <0.1, reflecting the dissolution of hydrous, Rb-rich minerals (white mica ± illite) with their radiogenic isotopic ingrowths liberated into surrounding andesitic magmas. Varied amounts of U/Pb, Th/Pb and Th/U fractionation demonstrably occurred between xenoliths and protoliths, but these are challenging to correlate with Pb isotopic fractionation that also occurred. One xenolith contains a vein of clinopyroxene, calcic plagioclase, silicic glass and graphite that formed when quartz + calcite veins were pyrometamorphosed. The vein-bearing xenolith possesses unusual chemical and isotopic features, which include a negative Ce anomaly, La/Yb ~2 and high Nd/Nd (0.51284), which are also reported for xenolithic material erupted at neighbouring Ruapehu volcano.

中文翻译：

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新西兰汤加里罗火山变沉积岩捕虏体的火变质作用引起的化学和同位素变化

新西兰北岛汤加里罗火山喷发的安山岩含有源自基岩的长石和石英捕虏体。新的主要氧化物、微量元素和 Sr-Nd-Pb 同位素数据表明，Waipapa 和 Kaweka（变）沉积地体均出现在喷发捕虏体中，而不是像之前认为的那样仅出现在 Kaweka 地体中。捕虏体矿物组合与其可能的来源材料不同，特别是缺乏白云母、伊利石、绿泥石和石英，这反映在化学和同位素组成的对比上。主量和微量元素数据表明，大多数捕虏体在约 800–980 °C 的温度下发生热变质时，体积质量减少了约 50%，这与典型的汤加里罗岩浆温度约 800–1000 °C 相似。保留了大部分 Eu 浓度（在残余斜长石中）；然而，捕虏体中的其他稀土元素通常低于原岩中的含量。在捕虏体中，原岩的 Nd/Nd 比率也被保留，这表明捕虏体来源于 Kaweka 和 Waipapa 地体，数量接近等量。相对于可能的原岩，捕虏体中的 Sr/Sr 比值降低了 0.003，同时 Rb/Sr 比值从 0.1-0.8 下降到 <0.1，反映了含水、富含 Rb 的矿物（白云母）的溶解。 ±伊利石）及其放射性同位素长入物释放到周围的安山岩浆中。捕虏体和原岩之间明显发生了不同量的 U/Pb、Th/Pb 和 Th/U 分馏，但很难将这些分馏与也发生的 Pb 同位素分馏联系起来。一块捕虏体含有单斜辉石、钙质斜长石、硅质玻璃和石墨的脉，这些是石英 + 方解石脉热变质时形成的。含脉捕虏体具有不寻常的化学和同位素特征，其中包括负 Ce 异常、La/Yb ~2 和高 Nd/Nd (0.51284)，这些特征在邻近的鲁阿佩胡火山喷发的捕虏体材料中也有报道。