Transition from orogenic-like to anorogenic magmatism in the Southern Alps during the Early Mesozoic: Evidence from elemental and Nd-Sr-Hf-Pb isotope geochemistry of alkali-rich dykes from the Finero Phlogopite Peridotite, Ivrea–Verbano Zone
Transition from orogenic-like to anorogenic magmatism in the Southern Alps during the Early Mesozoic: Evidence from elemental and Nd-Sr-Hf-Pb isotope geochemistry of alkali-rich dykes from the Finero Phlogopite Peridotite, Ivrea–Verbano Zone
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DOI：
10.1016/j.gr.2023.12.011
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发表时间：
2023-12
影响因子：
6.1
通讯作者：
Abimbola C. Ogunyele;M. Bonazzi;T. Giovanardi;M. Mazzucchelli;V. Salters;A. Decarlis;Alessio Sanfilippo;Alberto Zanetti
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作者：
Abimbola C. Ogunyele;M. Bonazzi;T. Giovanardi;M. Mazzucchelli;V. Salters;A. Decarlis;Alessio Sanfilippo;Alberto Zanetti
南阿尔卑斯山最西段的伊夫雷亚-韦尔巴诺带（IVZ）是亚得里亚板块标志性的上地幔到下大陆壳序列，为了解晚古生代到早中生代冈瓦纳-劳俄罗斯边界发生的构造岩浆事件提供了一个地质窗口。在这项工作中，我们记录了侵入 Finero 金云母橄榄岩（北部 IVZ）的早中生代富碱岩脉群的新地球化学和 Nd-Sr-Hf-Pb 同位素数据，为南阿尔卑斯山早中生代岩浆作用的性质、起源和演化提供了地质约束。研究的岩脉含有角闪石-金云母，并且显示出两个端元组之间不同的地球化学特征。岩脉群的特征是贫 HFSE、富铝角闪石（Al2O3 高达 16 wt%），具有高 LILE 和 LREE 含量、高放射性 87Sr/86Sr(i)（0.704732 至 0.704934）和低放射性 Nd 同位素（εNd(i)从 –0.1 至 –0.7），这支持了大量的出现母体地幔中回收的大陆地壳成分融化并赋予整体“类似造山”的亲和力。该岩脉群主要来源于交代化的岩石圈地幔源区。第二组富含 HFSE，其中富含 LILE 和 LREE 的贫铝角闪石、低放射性 87Sr/86Sr(i)(0.703761–0.704103) 和较高放射性 Nd 同位素（εNd(i)从 +3.4 到 +5.4），表明“非造山”碱性亲和力和软流圈到深部岩石圈地幔来源。一些岩脉同时表现出造山和非造山作用，这提供了IVZ中类造山岩浆作用早于碱性非造山岩浆作用的证据。因此，菲内罗岩脉群记录了南阿尔卑斯山早中生代岩浆作用的地球化学变化，从类造山岩浆作用（典型的碰撞后环境）到非造山碱性岩浆作用（常见于板内和伸展环境），并将 IVZ 早中生代岩浆作用与南阿尔卑斯山东部和中部地区的早中生代岩浆作用建立了时间关联。
The Ivrea-Verbano Zone (IVZ) in the westernmost sector of the Southern Alps is an iconic upper mantle to lower continental crust sequence of the Adriatic Plate and provides a geological window into the tectono-magmatic events that occurred at the Gondwana–Laurussia boundary from Late Paleozoic to Early Mesozoic. In this work, we document new geochemical and Nd-Sr-Hf-Pb isotopic data for Early Mesozoic alkali-rich dyke swarms which intruded the Finero Phlogopite Peridotite (northern IVZ) to provide geological constraints on the nature, origin and evolution of Early Mesozoic magmatism in the Southern Alps. The studied dykes are amphibole-phlogopite-bearing and show geochemical features varying between two end-member groups. A dyke group is characterized by HFSE-poor, Al-rich amphibole (Al2O3up to 16 wt%) with high LILE and LREE contents, high radiogenic87Sr/86Sr(i)(0.704732 to 0.704934) and low radiogenic Nd isotopes (εNd(i)from –0.1 to –0.7), which support the occurrence of significant amounts of recycled continental crust components in the parental mantle melts and impart an overall “orogenic-like” affinity. This dyke group was largely derived from metasomatized lithospheric mantle sources. The second group is HFSE-rich with Al-poorer amphibole enriched in LILE and LREE, low radiogenic87Sr/86Sr(i)(0.703761–0.704103) and higher radiogenic Nd isotopes (εNd(i)from +3.4 to +5.4) pointing to an “anorogenic” alkaline affinity and asthenospheric to deep lithospheric mantle sources. Some dykes show both orogenic and anorogenic affinities, providing evidence that the orogenic-like magmatism in the IVZ predates the alkaline anorogenic magmatism. The Finero dyke swarms therefore record a geochemical change of the Early Mesozoic magmatism of the Southern Alps from orogenic-like magmatism, typical of post-collisional settings, to anorogenic alkaline magmatism, common in intraplate to extensional settings, and places a temporal correlation of Early Mesozoic magmatism in the IVZ to those in the eastern and central sectors of the Southern Alps.