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The Tapes complex (Nico Pérez Terrane, Uruguay): Constraining the mesoproterozoic evolution of the Río de la Plata Craton
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.jsames.2020.102906
Claudio Gaucher , Robert Frei , Lucía Samaniego , Thomas M. Will , Farid Chemale , María Florencia Gargiulo , Daniel G. Poiré , Xiaoxiao Ling , Xian-Hua Li , Qiu-Li Li

Abstract The Tapes Complex crops out in the southeastern Nico Perez Terrane (NPT) of the Rio de la Plata Craton and forms part of a NE-trending Mesoproterozoic belt together with the Calymmian (1.48–1.43 Ga) Parque UTE and Mina Verdun groups. The complex is characterized by interbedded/tectonically interleaved metasedimentary (mainly siliciclastic) and metaultramafic rocks, with subordinate intercalations of metabasites, carbonate and chert, all metamorphosed in the greenschist facies. The age of the Tapes Complex is constrained by: (i) a U–Pb SIMS age of 1360 ± 12 Ma for the youngest detrital zircon, (ii) the K–Ar age of 1253 ± 32 Ma for synkinematic muscovite of the Zapican thrust, which affects the unit, and (iii) an Sm–Nd isochronic age of 1403 ± 150 Ma for ultramafic and mafic rocks. The intruding Tapes Chico Syenite yielded a much younger U–Pb SIMS age of 601 ± 5 Ma, associated with Brasiliano-Pan African tectonism, negative eHf values (mean = −31), δ18O zircon ratios ranging between 5.45 and 6.68‰ V-SMOW and inherited zircons dated at 1774-1756 Ma. The best preserved mafic and ultramafic samples yielded Nd model ages (TDM) between 1.55 and 1.68 Ga, close to the assumed crystallization age, and positive eNd(t). Nd model ages of metasedimentary rocks vary between 1.8 and 3.1 Ga, which is interpreted as reflecting two contrasting sources: Archean units of the NPT and Mesoproterozoic mafic and ultramafic rocks, including fragments of oceanic crust. Chondrite-normalized REE patterns of metasedimentary rocks are characterized by LREE enrichment and lack of an Eu anomaly, similar to REE patterns of co-occurring metabasalts. High MgO concentrations, high Cr/V and low Y/Ni and Th/Sc ratios imply the involvement of ultramafic rocks in the source area, which is also supported by whole-rock Pb isotope data. A geodynamic evolution is envisaged, from an extensional tectonic setting between 1.48–1.43 Ga (rift or retroarc basin) into a compressional, retroarc foreland basin at ca. 1.25–1.20 Ga, the latter being probably related to the Kibaran Orogeny in the Namaqua-Natal Belt. It is proposed that the corresponding arc granites and high-grade metamorphic rocks are likely to be found in one of the several terranes in the Namaqua sector of the belt. The Apiai Terrane (Ribeira Belt, Brazil) shows a similar geological record and evolution as the NPT, and maybe a fragment of the latter displaced to the NW by the Ibare Shear Zone. The Tapes Complex is a key unit for understanding the assembly of the Rio de la Plata and Kalahari cratons, and their incorporation into the Rodinia supercontinent.

中文翻译:

Tapes 复合体(Nico Pérez Terrane,乌拉圭):限制拉普拉塔克拉通的中元古代演化

摘要 Tapes 杂岩在拉普拉塔克拉通东南部的 Nico Perez Terrane (NPT) 中出露,与 Calymmian (1.48–1.43 Ga) Parque UTE 和 Mina Verdun 群一起构成了向东北走向的中元古代带的一部分。该杂岩体的特征是互层/构造交错的变质沉积岩(主要是硅质碎屑)和变质镁铁质岩,以及变质岩、碳酸盐和燧石的次要夹层,均在绿片岩相中变质。Tapes 复合体的年龄受到以下因素的限制:(i) 最年轻碎屑锆石的 U-Pb SIMS 年龄为 1360 ± 12 Ma,(ii) Zapican 冲断层的同运动白云母的 K-Ar 年龄为 1253 ± 32 Ma ,这会影响单元,以及(iii)超基性和基性岩的 Sm-Nd 等时年龄为 1403 ± 150 Ma。侵入的奇科正长岩带产生了一个更年轻的 U-Pb SIMS 年龄为 601 ± 5 Ma,与巴西-泛非构造运动、负 eHf 值(平均值 = -31)、δ18O 锆石比率范围在 5.45 和 6.68‰ V-SMOW 之间和 1774-1756 Ma 的继承锆石。保存最完好的镁铁质和超镁铁质样品产生的 Nd 模型年龄 (TDM) 介于 1.55 和 1.68 Ga 之间,接近假定的结晶年龄,并且 eNd(t) 为正。变沉积岩的 Nd 模型年龄在 1.8 和 3.1 Ga 之间变化,这被解释为反映了两个截然不同的来源:NPT 的太古代单元和中元古代基性和超基性岩,包括大洋地壳的碎片。变沉积岩的球粒陨石归一化 REE 模式的特征是 LREE 富集和缺乏 Eu 异常,类似于共生变玄武岩的 REE 模式。高 MgO 浓度、高 Cr/V 和低 Y/Ni 和 Th/Sc 比意味着超基性岩在源区的参与,这也得到了全岩 Pb 同位素数据的支持。设想地球动力学演化,从 1.48-1.43 Ga(裂谷或弧后盆地)之间的伸展构造环境到约 1.25-1.20 Ga,后者可能与 Namaqua-Natal 带的 Kibaran 造山带有关。据推测,相应的弧形花岗岩和高等级变质岩很可能在该带 Namaqua 部分的几个地体之一中发现。Apiai Terrane(巴西里贝拉带)显示出与 NPT 相似的地质记录和演化,并且可能是后者的一部分被 Ibare 剪切带移至 NW。
更新日期:2021-01-01
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