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Cenozoic Italian magmatism - Isotope constraints for possible plume-related activity

机译：新生代意大利岩浆作用-可能与羽流有关的活动的同位素约束

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摘要

Assessment of the isotope systematics and the magmatotectonic history of mainly Cenozoic igneous rocks from Italy shows them to be inconsistent with subduction-related magmatism. We attempt to fit these data into an alternative model involving long-term, recurrent plume activity that extended over a period of about 100 Ma, that involved mantle expansion and subsequent mixing between isotopically-distinct, mantle components. Sr, Nd and Pb isotopic compositions of Cenozoic Italian igneous rocks, rather than being random, reflect binary mixing involving a common end-member similar to FOZO. Most isotopic data from along the entire length of Italy, from the Aeolian Islands to the Alpine belt, define a Main Italian Radiogenic Trend (MIRT), characterized by mixing between FOZO and a highly radiogenic Sr, mantle end-member (ITEM, ITalian Enriched Mantle). Data from the Adria foreland, Sicily and the south-western Tyrrhenian Sea and Sardinia deviate from MIRT suggesting mixing with other components, perhaps HIMU and EMI. Both the absence of pure DMM, and the presence of isotopic end-members not recognized in present-day consuming-plate margins are incompatible with subduction-related models. Two models are discussed, one in which ITEM is attributed to melting of pre-Alpine sediments/upper continental crust entrained in a FOZO-like mantle and the other to widespread metasomatic activity involving deep-seated plume activity. In the latter, the widespread nature of FOZO is attributed to a late Triassic-early Jurassic plume that preceded the opening of the Alpine Tethys and led to modification of the lithosphere and/or asthenosphere. Late Jurassic-early Cretaceous plume activity produced mantle expansion and the opening of the Alpine Tethys. A new phase of plume activity started during the Oligocene with the opening of the western and central Mediterranean Basins. Stretching and large-scale extension of the Mediterranean lithosphere was caused by the progressive eastward growth and volume increase of a plume head trapped within the Transition Zone. Plume-generated fluids/melts enriched in K-Ca-CO_2-H_2O, produced mantle sources capable of generating widespread alkaline, mafic, and carbonatitic magmatism. Lithospheric unloading controlled the Tyrrhenian and peri-Tyrrhenian magmatic activity.
机译：对意大利主要新生代火成岩的同位素系统学和岩浆构造历史的评估表明，它们与俯冲相关的岩浆作用不一致。我们试图将这些数据拟合到一个替代模型中，该模型涉及一个长期的，周期性的羽流活动，该活动持续了大约100 Ma的时间，其中包括地幔膨胀和随后同位素不同的地幔组分之间的混合。新生代意大利火成岩的Sr，Nd和Pb同位素组成不是随机的，反映的是二进制混合，涉及与FOZO类似的常见末端。从整个意大利到从风成群岛到高山带的大部分同位素数据，都定义了意大利主要的放射成因趋势（MIRT），其特征是FOZO和高度放射成因的Sr地幔末段成员（ITEM，ITalian Enriched）地幔）。来自阿德里亚前陆，西西里岛和西南第勒尼安海和撒丁岛的数据偏离了MIRT，表明与其他成分混合，可能是HIMU和EMI。既不存在纯数字万用表，也没有在当今的消耗板边缘中识别出的同位素末端成员都与俯冲相关模型不兼容。讨论了两个模型，其中一个ITEM归因于FOZO状地幔中夹带的高山前沉积物/上部大陆壳的融化，另一个归因于涉及深部羽流活动的广泛的交代活动。在后者中，FOZO的广泛性归因于晚三叠世-早侏罗纪羽状流，该羽状流早于高山特提斯山的开放并导致岩石圈和/或软流圈的变质。侏罗纪晚期至白垩纪早期的羽流活动引起地幔膨胀和高山特提斯山脉的开放。渐新世期间，地中海盆地西部和中部开放，羽流活动进入了一个新的阶段。地中海岩石圈的伸展和大规模扩张是由于过渡带内滞留的羽状喷头逐渐向东生长和体积增加引起的。羽流产生的富含K-Ca-CO_2-H_2O的流体/熔体产生了能够产生广泛的碱，铁镁质和碳岩性岩浆作用的地幔源。岩石圈卸荷控制了第勒尼安和第勒尼安山脉的岩浆活动。

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  • 来源
    《Journal of South American earth sciences》 |2013年第1期|22-40|共19页
  • 作者

    K. Bell; G. Lavecchia; G. Rosatelli;

  • 作者单位

    Department of Earth Sciences, Carleton University, Ottawa, Ontario K1S 5B6, Canada;

    DiSPUTer, Earth Science Section, "G. d'Annunno" University, Madonna delle Piane University Campus, 66100 Chieti, Italy;

    DiSPUTer, Earth Science Section, "G. d'Annunno" University, Madonna delle Piane University Campus, 66100 Chieti, Italy;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    italy; magmatism; radiogenic isotopes; plumes; geodynamics;

    机译：意大利;岩浆作用放射性同位素羽地球动力学;

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