The Araçuaí Orogen (AO) has been interpreted as a Neoproterozoic example of a large, “hot” orogen, based on a broad zone (250 km) of midcrustal metamorphic assemblages with a long, 70‐Myr history of crustal melting and episodic magmatism throughout the late Neoproterozoic and earliest Paleozoic. Here, we present results of U‐Pb sensitive high‐resoution ion microprobe (SHRIMP) zircon dating and detailed anisotropy of magnetic susceptibility (AMS) study on a late Cambrian, bimodal pluton related to final period of collapse of the AO. New U‐Pb zircon ages constrain the crystallization age of different suites within the Santa Angélica Pluton, 506 ± 3 Ma for the early felsic phase and 498 ± 5 Ma for the mafic core. New AMS data indicate that the emplacement of the Santa Angélica Pluton corresponds to two coupled plutons with concentric structures arrayed about a twin, bull's eye pattern. During the final stages of intrusion, upward relative movement of the northeastern lobe exposed the deeper levels of the intrusion, relative to the more shallowly eroded southwestern lobe. These observations suggest that magma emplacement was controlled by magma buoyancy forces, with little influence of regional tectonic stress. This behavior contrasts with the well‐defined, tectonic‐controlled fabrics of coeval plutons occurring to the north which was still hot, therefore highlighting the contrasting thermal evolution between different sectors of the orogen during its final stages.

中文翻译：

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新元古代Araçuaí造山带中寒武纪“各向同性”岩体的磁性结构和年代学

阿拉索阿造山带（AO）被解释为大型，“热”造山带的新元古代例子，它基于中地壳变质组合的广阔区域（250公里），并且在整个地壳中有很长的70多年的地壳融化和偶发性岩浆作用新元古代晚期和最早的古生代。在这里，我们介绍了U-Pb敏感的高离析离子微探针（SHRIMP）锆石测年的结果以及磁化率（AMS）的详细各向异性研究，该研究与晚期AO崩塌有关的寒武纪双峰岩体。新的U‐Pb锆石年龄限制了SantaAngélicaPluton内不同套件的结晶年龄，早期长英质期为506±3 Ma，镁铁质岩心为498±5 Ma。新的AMS数据表明，圣安格利卡岩体的位置对应于两个耦合的岩体，其同心结构排列在双胞胎的牛眼图案上。在入侵的最后阶段，相对于较浅侵蚀的西南叶，东北叶的向上相对运动暴露了更深的入侵水平。这些观察结果表明，岩浆位置受岩浆浮力控制，而对区域构造应力的影响很小。这种行为与北半球仍然很热的，构造清晰，受构造控制的上等古陆成岩形成鲜明对比，因此突出了造山带不同阶段末期热演化的对比。相对于较浅侵蚀的西南叶，东北叶的向上相对运动暴露了更深的侵入。这些观察结果表明，岩浆位置受岩浆浮力控制，而对区域构造应力的影响很小。这种行为与北半球仍然很热的，构造清晰，受构造控制的上等古陆成岩形成鲜明对比，因此突出了造山带不同阶段末期热演化的对比。相对于较浅侵蚀的西南叶，东北叶的向上相对运动暴露了更深的侵入。这些观察结果表明，岩浆位置受岩浆浮力控制，而对区域构造应力的影响很小。这种行为与北半球仍然发育的，构造清晰，受构造控制的同卵小行星的构造形成了鲜明对比，因此突出了造山带不同阶段最后阶段热演化的对比。