98Mo/95Mo and 238U/235U in lamproites, shoshonites, and high-K calc-alkaline rocks from Western Alps: inferences on their genesis

IF 1 4区地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY

Italian Journal of Geosciences Pub Date : 2018-10-01 DOI:10.3301/IJG.2018.20

M. Casalini

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引用次数: 8

Abstract

Oligocene ultrapotassic and associated potassic rocks from Western Alps derived from the crystallisation of magmas originated from partial melting of mantle sources extremely enriched in recycled crustal components. These rocks are well suited for studying the effects of subduction-related, sediment-derived metasomatism on Molybdenum and Uranium isotopes. This paper reports the first 98Mo/95Mo and 238U/235U data on potassic and ultrapotassic rocks at destructive plate margins. Both 98Mo/95Mo and 238U/235U ratios show large variations in the samples from Western Alps. U isotope compositions are consistent with an increasing role of metasomatising melts from recycled sediments, which explains the variable enrichment in potassium and incompatible trace elements passing from high-K calc-alkaline to lamproitic magmas through shoshonitic ones. The variation of Mo isotope compositions is more complex due to the extreme depletion in Mo observed and since their values exceed the range observed for volcanic arcs. These features were investigated considering several possible processes such as secondary weathering, hosting of Mo related to residual mineral phases during sediment melting or physical removal during subduction. The results were also discussed in the framework of the complex processes responsible for the genesis and geochemical characteristics of the Tethyan Realm Lamproites, particularly in relationship with the exotic SALATHO geochemical component.

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西阿尔卑斯煌斑岩、闪玄岩和高钾钙碱性岩中98Mo/95Mo和238U/235U的成因推断

来自西阿尔卑斯山的渐新世超钾岩和伴生钾岩，源于地幔源的部分熔融岩浆结晶，地幔源极为富集再循环地壳成分。这些岩石非常适合研究俯冲相关的沉积物交代作用对钼和铀同位素的影响。本文报道了破坏性板块边缘钾质和超钾质岩石的第一批98Mo/95Mo和238U/235U数据。98Mo/95Mo和238U/235U的比值在来自西阿尔卑斯山的样品中都显示出较大的变化。U同位素组成与再循环沉积物中交代熔体的作用越来越大一致，这解释了钾和不相容微量元素从高钾钙碱性岩浆到煌斑岩岩浆再到钠玄质岩浆的可变富集。钼同位素组成的变化更为复杂，这是由于观测到的钼的极度贫化，以及它们的值超过了火山弧的观测范围。研究这些特征时考虑了几个可能的过程，如次生风化、沉积物熔融过程中与残余矿物相有关的Mo的存在或俯冲过程中的物理去除。这些结果也在复杂过程的框架内进行了讨论，这些复杂过程是Tethyan Realm Lamproites的成因和地球化学特征的原因，特别是与外来SALATHO地球化学成分的关系。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Italian Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-

CiteScore

2.90

自引率

11.10%

发文量

审稿时长

>12 weeks

期刊介绍： The Italian Journal of Geosciences (born from the merging of the Bollettino della Società Geologica Italiana and the Bollettino del Servizio Geologico d''Italia) provides an international outlet for the publication of high-quality original research contributions in the broad field of the geosciences. It publishes research papers, special short papers, review papers, discussion-and-replies for their rapid distribution to the international geosciences community. The journal is firstly intended to call attention to the Italian territory and the adjacent areas for the exceptional role they play in the understanding of geological processes, in the development of modern geology and the Earth sciences in general. The main focus of the journal is on the geology of Italy and the surrounding sedimentary basins and landmasses, and on their relationships with the Mediterranean geology and geodynamics. Nevertheless, manuscripts on process-oriented and regional studies concerning any other area of the World are also considered for publication. Papers on structural geology, stratigraphy, sedimentology, basin analysis, paleontology, ecosystems, paleoceanography, paleoclimatology, planetary sciences, geomorphology, volcanology, mineralogy, geochemistry, petrology, geophysics, geodynamics, hydrogeology, geohazards, marine and engineering geology, modelling of geological process, history of geology, the conservation of the geological heritage, and all related applied sciences are welcome.