Abstract An ensemble of fifteen granodiorite/tonalite plutons and minor intrusions was generated during Cambro-Ordovician times (ca. 498–462 Ma) at the margin of Gondwana, which occupies a large portion of the Central Iberian Zone of the Iberian Massif (Spain and Portugal). This ensemble is known as the Beira-Extremadura batholith (BEB), which is mainly composed of tonalities and granodiorites (>90 vol%) and shows an atypical composition, with values of ASI (alumina saturation index) ≈ 1.2 on average, and marked calc-alkaline affinity in terms of major and trace elements. SHRIMP zircon U-Pb ages of 476 ± 7 Ma, 476 ± 6 Ma, and 474 ± 7 Ma for Montanchez, Santa Cruz de la Sierra and Valdemorales tonalites, respectively, coincide within uncertainty with the age of other Lower Ordovician BEB intrusions. Analysis of phase relations and comparisons with experimental results on cotectic liquid compositions, indicate that these atypical rocks represent calc-alkaline magmas that carried exogenous pelitic restites from depth. Assimilation of partially molten metasediments by invasion of calc-alkaline magmas is a plausible explanation. Model mixing of experimental calc-alkaline liquids and Ediacaran metasedimentary rocks yields that 20% (up to 40% in samples of the Santa Cruz Pluton) of assimilated metagreywackes and metapelites is required to account for geochemical atypical compositions departing from a main cotectic array of calc-alkaline systems. The processes of melting or melting plus assimilation are favored by addition of water-rich fluids. We propose a tectonic scenario of crustal extension and metasomatized mantle melting that supplied hydrous intermediate magmas to the crust triggering crustal melting and massive assimilation of metasediments.

中文翻译：

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来自伊比利亚南部的非典型冈瓦纳周围花岗闪长岩-色调长岩岩浆作用。岩浆的起源和影响

摘要 在冈瓦纳大陆边缘的寒武纪-奥陶纪时期（约 498-462 Ma）产生了 15 个花岗闪长岩 / 斑长岩体和少量侵入体的集合，该岩体占据了伊比利亚地块（西班牙和葡萄牙）。该集合被称为贝拉-埃斯特雷马杜拉岩基（BEB），主要由色调和花岗闪长岩（>90 vol%）组成，成分不典型，平均 ASI（氧化铝饱和指数）≈ 1.2，标记为主要和微量元素的钙碱亲和力。Montanchez、Santa Cruz de la Sierra 和 Valdemorales 色调岩的 SHRIMP 锆石 U-Pb 年龄分别为 476 ± 7 Ma、476 ± 6 Ma 和 474 ± 7 Ma，与其他下奥陶统 BEB 侵入岩的年龄相吻合。相关系分析以及与共晶液体成分实验结果的比较表明，这些非典型岩石代表了钙碱性岩浆，从深处携带外源泥质岩浆。钙碱性岩浆的侵入对部分熔融变质沉积物的同化是一个合理的解释。实验钙碱性液体和埃迪卡拉纪变质沉积岩的模型混合产生 20%（在圣克鲁斯深体的样品中高达 40%）的同化变灰泥岩和变泥质岩需要考虑地球化学非典型成分，该成分偏离主要的钙质共晶阵列- 碱性系统。添加富水流体有利于熔化或熔化加同化过程。