We report a study of whole-rock O–H–Sr–Nd isotopes of Ordovician igneous and metamorphic rocks exposed at different crustal palaeodepths along c. 750 km in the Sierras Pampeanas, NW Argentina. The isotope compositions preserved in the intermediate rocks (mostly tonalite) (average δ18O = +8.7 ± 0.5‰, δD = −73 ± 14‰, 87Sr/86Srt = 0.7088 ± 0.0001 and εNdt = −4.5 ± 0.6) show no major difference from those of most of the mafic rocks (average δ18O = +8 ± 0.8‰, δD = −84 ± 18‰, 87Sr/86Srt = 0.7082 ± 0.0016 and εNdt = −4 ± 1.1), suggesting that most of their magmas acquired their crustal characteristics in the mantle. The estimate of assimilation of crustal material (δ18O = +12.2 ± 1.7‰, δD = −89 ± 21‰, 87Sr/86Srt = 0.7146 ± 0.0034 and εNdt = −6.9 ± 0.7) by the tonalite is in most samples within the range 10–20%. Felsic magmas that reached upper crustal levels had isotope values (δ18O = +9.9 ± 1.5‰, δD= −76 ± 5‰, 87Sr/86Srt = 0.7067 ± 0.0010, εNdt = −3.5 ± 1.4) suggesting that they were not derived by fractionation of the contaminated intermediate magmas, but evolved from different magma batches. Some rocks of the arc, both igneous (mostly gabbro and tonalite) and metamorphic, underwent restricted interaction with meteoric fluids. Reported values of δ18O of magmatic zircons from the Famatinian arc rocks (+6 to +9‰) are comparable to our δ18O whole-rock data, indicating that pervasive oxygen isotope exchange in the lower crust was not a major process after zircon crystallization.

中文翻译：

---

O-H-Sr-Nd 同位素对阿根廷西北部法马提尼期岩浆弧起源的限制

我们报告了在不同地壳古深度暴露的奥陶纪火成岩和变质岩的全岩 O-H-Sr-Nd 同位素研究C。750 公里，位于阿根廷西北部的 Sierras Pampeanas。保留在中间岩石（主要是英云母）中的同位素组成（平均 δ18O = +8.7 ± 0.5‰，δD = -73 ± 14‰，87锶/86锶吨= 0.7088 ± 0.0001 和 εNd吨= -4.5 ± 0.6) 与大多数镁铁质岩石（平均 δ18O = +8 ± 0.8‰，δD = -84 ± 18‰，87锶/86锶吨= 0.7082 ± 0.0016 和 εNd吨= -4 ± 1.1），表明它们的大部分岩浆在地幔中获得了它们的地壳特征。地壳物质同化的估计（δ18O = +12.2 ± 1.7‰，δD = -89 ± 21‰，87锶/86锶吨= 0.7146 ± 0.0034 和 εNd吨= -6.9 ± 0.7)，在大多数样品中，英云母在 10–20% 范围内。达到上地壳水平的长英质岩浆具有同位素值（δ18O = +9.9 ± 1.5‰，δD= -76 ± 5‰，87锶/86锶吨= 0.7067 ± 0.0010, εNd吨= -3.5 ± 1.4）表明它们不是由受污染的中间岩浆分馏衍生的，而是从不同的岩浆批次演化而来。弧形的一些岩石，无论是火成岩（主要是辉长岩和云闪石）还是变质岩，都与大气流体进行了有限的相互作用。报告的 δ 值18来自法马蒂尼弧岩的岩浆锆石的 O (+6 至 +9‰) 与我们的 δ 相当18O 全岩数据，表明下地壳中普遍存在的氧同位素交换不是锆石结晶后的主要过程。