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首页> 外文期刊>Contributions to Mineralogy and Petrology >(Campi Flegrei caldera, Italy) plutonic clasts and their relation to the Campanian ignimbrite
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(Campi Flegrei caldera, Italy) plutonic clasts and their relation to the Campanian ignimbrite

机译：（意大利的Campi Flegrei火山口）深部碎屑及其与Campanian火成岩的关系

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The Campi Flegrei volcanic district (Naples region, Italy) is a 12-km-wide, restless caldera system that has erupted at least six voluminous ignimbrites during the late Pleistocene, including the >300 km3 Campanian ignimbrite (CI) which originated from the largest known volcanic event of the Mediterranean region. The Breccia Museo (BM), a petrologically heterogeneous and strati-graphically complex volcanic deposit extending over 200 km2 in close proximity to Campi Flegrei, has long remained contentious regarding its age and stratigraphic relation to the CI. Here, we present crystallization and eruption ages for BM plutonic ejecta clasts that were determined via uranium decay series and (U-Th)/He dating of zircon, respectively. Despite mineralogical and textural heterogeneity of these syenitic clasts, their U-Th zircon rim crystallization ages are indistinguishable with an average age of 49.7 ± 2.5 ka (2a errors; mean square of weighted deviates MSWD =1.2; n = 34). A subset of these crystals was used to obtain disequilibrium-corrected (U-Th)/He zircon ages which average 41.7 ± 1.8 ka (probability of fit P = 0.54; n = 15). This age closely overlaps with published CI ~(40)Ar/~(39)Ar eruption ages (40.6 ± 0.1 ka) after recalibration to recently revised flux monitor ages. Concordant eruption ages for BM and CI agree with previous chemostratigraphic and paleomagnetic correlations, suggesting their origin from the same eruption. However, they are at variance with recalibrated ~(40)Ar/~(39)Ar ages which have BM postdate CI by 3 ± 1 ka. BM syenites show similar geochemical and Sr-Nd iso-topical features of pre-caldera rocks erupted between 58 and 46 ka, but are distinctive from subsequent caldera-forming magmas. Energy-constrained assimilation and fractional crystallization modeling of Nd-Sr isotopic data suggests that pre-caldera magmas formed a carapace of BM-type intrusions in a mid-crust magma chamber (>8 km depth) shielding the younger Cl magma from contamination by Hercynian basement wall rocks. An ~41-50 ka hiatus in crystallization ages implies rapid solidification of these pre-Cl intrusions. This argues against protracted pre-eruptive storage of a large volume of Cl magma at shallow crustal levels.
机译：Campi Flegrei火山区（意大利那不勒斯地区）是一个12公里宽的，不安定的火山口系统，在晚更新世晚期至少喷出了六块大量的火成岩，包括大于300 km3的Campanian火成岩（CI）。地中海地区已知的火山事件。 Breccia Museo（BM）是一种岩石异质性和地层复杂的火山岩，延伸超过200平方公里，紧邻Campi Flegrei，关于其年龄和与CI的地层关系，一直存在争议。在这里，我们介绍了分别通过铀衰变系列和锆石的（U-Th）/ He测年确定的BM多发性射出物碎屑的结晶和萌发年龄。尽管这些榴辉岩碎屑在矿物学和质地上存在异质性，但它们的U-Th锆石边缘结晶年龄却无法区分，平均年龄为49.7±2.5 ka（2a误差;加权均方差MSWD = 1.2; n = 34）。这些晶体的一个子集用于获得平均平衡为41.7±1.8 ka的不平衡校正（U-Th）/ He锆石年龄（拟合概率P = 0.54; n = 15）。在重新校准到最近修订的流量监测器年龄之后，该年龄与已公布的CI〜（40）Ar /〜（39）Ar爆发年龄（40.6±0.1 ka）紧密重叠。 BM和CI的一致喷发年龄与以前的化学地层和古地磁相关性一致，表明它们的起源是相同的喷发。但是，它们与重新校准的〜（40）Ar /〜（39）Ar年龄存在差异，这些年龄具有BM后CI达3±1 ka。 BM榴辉岩在58至46 ka之间喷出的火山口前岩石显示出相似的地球化学特征和Sr-Nd同位素特征，但与随后的火山口形成岩浆不同。 Nd-Sr同位素数据的能量受限同化和分步结晶模型表明，破火山口前岩浆在中地壳岩浆室内（> 8 km深度）形成了BM型侵入的甲壳，从而保护了较年轻的Cl岩浆不受海西氏污染的影响地下室围岩。结晶时代的〜41-50 ka裂隙意味着这些前Cl侵入体的快速凝固。这与在浅地壳水平长期大量喷出的岩浆的喷发前储藏不符。

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