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首页> 外文期刊>Contributions to Mineralogy and Petrology >Linking the thermal evolution and emplacement history of an upper-crustal pluton to its lower-crustal roots using zircon geochronology and geochemistry (southern Adamello batholith, N. Italy)
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Linking the thermal evolution and emplacement history of an upper-crustal pluton to its lower-crustal roots using zircon geochronology and geochemistry (southern Adamello batholith, N. Italy)

机译：使用锆石年代学和地球化学方法将上地壳的热演化和沉积历史与其下地壳的根源联系起来（意大利北部的Adamello Batholith，南）

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摘要

The Val Fredda igneous complex in the southern Adamello batholith (N. Italy) consists of dioritic to gabbroic sills and dykes that were injected at 6-10 km depth into partly crystallized tonalites and granodiorites. High-precision U-Pb age determinations by chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) show very similar dispersion of zircon U-Pb dates over 90-200 ka and identical age distributions with a dominant mode at 42.5 Ma for six samples ranging in composition from gabbro to granodiorite. The co-variation of the probability density curves of zircon dates from mafic and felsic units suggests that they shared a common thermal history with periods of enhanced and reduced zircon growth, reflecting lowered and increased magma temperatures, respectively. However, trace element compositions, Ti-in-zircon temperatures and Hf isotopic compositions of zircon from mafic lithologies are distinctly different from those in felsic zircon and suggest their crystallization occurred in isotopically and chemically diverse magma batches. These magma batches formed in the lower crust from mingling and mixing of residual melts (derived from fractional crystallization of mainly amphibole from basaltic melt) with crustal partial melts at high temperatures above zircon saturation. Zircons crystallized during incipient cooling of these magmas and were entrained into the ascending melts, which were emplaced and rapidly solidified in the upper crust. The reported age dispersions imply that fractional crystallization and hybridization in the lower-to-middle crust, ascent into the upper crust and solidification did not last for more than 200 ka. The small magma volumes and flux also preclude significant zircon crystallization at the upper crustal emplacement level.
机译：位于南部阿达梅洛岩床（意大利北部）的瓦尔·弗雷达（Val Fredda）火成岩复合体由闪长岩到辉长岩的基岩和堤坝组成，并在6-10 km的深度注入部分结晶的同色岩和花岗闪长岩。通过化学磨损同位素稀释热电离质谱法（CA-ID-TIMS）进行的高精度U-Pb年龄测定显示，锆石U-Pb年龄分布在90-200 ka范围内非常相似，并且年龄分布相同，主导模式为42.5 Ma从辉长岩到花岗闪长岩的六个样品。镁铁质单位和长英质单位的锆石概率密度曲线的协变表明，它们具有共同的热历史，锆石的生长周期增加和减少，分别反映了岩浆温度的降低和升高。但是，镁铁质岩性锆石的微量元素组成，锆石中钛的温度和H同位素组成与长英石中的锆石明显不同，这表明它们的结晶发生在同位素和化学不同的岩浆批次中。这些岩浆在下部地壳中是由残余熔体（源自玄武质熔体的主要闪石的分步结晶）与地壳部分熔体在高于锆石饱和度的高温下混合和混合而形成的。锆石在这些岩浆开始冷却期间结晶，并被带入上升的熔体中，这些熔体被安置并迅速固化在上地壳中。报道的年龄弥散表明，从下到中地壳的部分结晶和杂化，到上地壳的上升和固化的持续时间不超过200 ka。较小的岩浆体积和通量也排除了锆石在上地壳沉积水平上的明显结晶。

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