The Onano eruption (~ 0.17 Ma) is the second to last caldera-forming eruption of the Latera volcano, in the northernmost sector of the Roman Comagmatic Province (Latium, Italy). The stratigraphic sequence, from base to top, includes ash and pumice-rich flow deposits, spatter-rich flow deposits and lag breccias associated with ash-rich flow deposits. By combining major and trace element compositions of the bulk rocks, matrix glasses and minerals of juvenile components from the different depositional units, we reconstruct the pre-eruptive evolution of the magma chamber and the syn-eruptive magma dynamics. Juvenile clasts with heterogeneous glass composition and/or mineral assemblage are a ubiquitous feature of the Onano eruption. The products cover a large compositional range from phonotephrite to phonolite. They are crystal poor, with felsic paragenesis associated to Mg-rich olivine (Fo82–90) and diopside (Fs4–7), these last not in equilibrium with the erupted melts. The mafic mineral assemblage suggests that the pre-eruption magma reservoir was periodically perturbed by the arrival of a primitive magma carrying on Mg-rich minerals and/or remobilizing a mafic crystal mush at the bottom of the reservoir. According to the results obtained from both rhyolite-MELTS and Rayleigh crystal fractionation modeling, we infer that the system evolved from phonotephrite to phonolite both via crystal fractionation and magma mixing between the two end members. Crystallization mostly proceeded at the wall of the reservoir, while magma mixing in the middle zones of the chamber generated the intermediate tephriphonolitic melts. The pre-eruptive chemical zoning was disrupted during the course of the eruption due to the simultaneous withdrawal of magma from different portions of the reservoir. During the first phase of the eruption, high-silica tephriphonolitic to phonolitic melts, residing in the upper part of the reservoir, were emitted with less involvement of the deeper phonotephrite. Phonotephritic magmas, with only a minor contribution of evolved melts, were later erupted as spatter-rich pyroclastic flows that preceded the main caldera collapse. During the caldera collapse, the whole reservoir was involved, leading to extensive and intimate syn-eruption mingling of the different melts. A comparison between the Onano eruption and other eruptions of the Italian high potassic volcanism provides new insights into the evolution of the Roman Comagmatic Province magmas and their eruptive processes.

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Onano 喷发（意大利中部拉特拉火山）：岩浆混合/混合作为火山口形成喷发的主要过程的一个例子

Onano 喷发 (~ 0.17 Ma) 是拉特拉火山的倒数第二次火山喷发，位于罗马 Comagmatic 省（意大利 Latium）的最北端。地层序列，从底部到顶部，包括富含灰分和浮石的流动沉积物、富含飞溅物的流动沉积物和与富含灰分的流动沉积物相关的滞后角砾岩。通过结合来自不同沉积单元的大块岩石、基质玻璃和矿物的主要和微量元素组成，我们重建了岩浆房喷发前的演化和同步喷发的岩浆动力学。具有异质玻璃成分和/或矿物组合的幼年碎屑是 Onano 喷发的一个普遍特征。产品涵盖了从音素石到音石的广泛成分范围。他们是水晶般的贫穷，与富镁橄榄石 (Fo82-90) 和透辉石 (Fs4-7) 相关的长英质共生作用，这些与喷发的熔体持续不平衡。基性矿物组合表明喷发前的岩浆储层因携带富镁矿物的原始岩浆的到来和/或在储层底部重新移动基性晶体糊状物而周期性地受到扰动。根据流纹岩-MELTS 和瑞利晶体分馏模型获得的结果，我们推断该系统是通过晶体分馏和两个端部之间的岩浆混合从音素岩演化为音长岩的。结晶主要在储层壁处进行，而岩浆在腔室中间区域的混合产生了中间的 tephriphonolitic 熔体。由于岩浆从储层的不同部分同时撤出，喷发前的化学分区在喷发过程中被破坏。在喷发的第一阶段，位于储层上部的高硅质 tephriphonolitic 到 phonolitic 熔体被喷出，而较深的 phonotephrite 参与较少。光辉质岩浆，只有少量的演化熔体，后来在主要火山口坍塌之前作为富含飞溅物的火山碎屑流喷发。在火山口坍塌期间，整个水库都被卷入，导致不同熔体广泛而密切的协同喷发混合。