Abstract The composite dikes of the Zimbros Bay in the Porto Belo-Bombinhas region, southern Brazil, are emplaced in the late stages of post-collisional magmatism, at ca. 590 Ma as NE-striking, subvertical tabular bodies intrusive in basement orthogneisses. The composite dikes are formed by a felsic core containing a swarm of mafic microgranular enclaves, bordered on both sides by mafic material of irregular thickness, and individual mafic dikes parallel to the main intrusion. The felsic and mafic rocks contain a well-developed magmatic foliation with solid-state deformation near the contacts. Stretching lineation is horizontal to sub-horizontal and better developed in the felsic rocks. The absence of a well-developed linear fabric in the mafic rocks hinders investigation of their emplacement based on conventional structural data. In order to investigate/explore the relationship between contemporaneous mafic and felsic rocks, as well as to understand the emplacement of these intrusions in relation to the transcurrent tectonics, a study on the magnetic fabric was made using anisotropy of magnetic susceptibility (AMS) and rock magnetism techniques for composite and individual mafic dikes. Magnetic mineralogy of both dikes is predominantly controlled by ferromagnetic minerals (e.g. magnetite and Ti-poor tinanomagnetite), with little contribution of paramagnetic minerals. The rock magnetism study shows that the magnetite grains have varied sizes. Individual mafic dikes have small grain sizes, whilst in the mafic borders, sizes vary from small to large. Felsic cores have large grain sizes. SEM data show oxyexsolution textures in the felsic core samples and in samples of individual mafic dikes. Only Ilmenite is found in the mafic border samples, either as anhedral grains or as thin lamellae, interpreted to result from intense oxyexsolution of magnetite. Increasing oxyexsolution degrees observed in samples from individual mafic dikes to felsic cores and mafic borders suggest different degrees of interaction between the original magmas. The studied intrusions show normal magnetic fabrics, with subvertical magnetic foliation (k1-k2 plane) and subhorizontal (k1) lineation. Magnetic data are concordant with structural field measurements and indicate sub-horizontal magma flow during emplacement. The much larger volume and size of enclaves found in the southern portion of the dike is compatible with its northward directed emplacement. The obtained magnetic data are also in agreement with the syntectonic emplacement of the composite dikes relative to the transcurrent movement of the Major Gercino Shear Zone.

中文翻译：

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巴西南部复合岩脉中对比成分的相互作用同构造岩浆的磁性织物数据

摘要 巴西南部 Porto Belo-Bombinhas 地区 Zimbros 湾的复合岩脉位于碰撞后岩浆作用的晚期阶段，大约在 590 Ma 作为侵入基底正片麻岩中的 NE 突出的、近垂直的板状天体。复合岩脉由长英质岩心构成，岩心包含大量镁铁质微粒包体，两侧以不规则厚度的镁铁质材料为边界，独立的镁铁质岩脉与主要侵入体平行。长英质和镁铁质岩石包含发育良好的岩浆叶理，在接触面附近发生固态变形。伸展线理从水平到次水平，在长英质岩中发育较好。镁铁质岩石中缺乏发育良好的线性结构阻碍了基于常规结构数据对其就位的研究。为了调查/探索同期基性岩和长英质岩之间的关系，以及了解这些侵入体相对于横流构造的侵位，利用磁化率 (AMS) 和岩石的各向异性对磁性结构进行了研究复合和单个基性岩脉的磁性技术。两个岩脉的磁性矿物学主要由铁磁性矿物（例如磁铁矿和贫钛锡磁铁矿）控制，顺磁性矿物的贡献很小。岩石磁性研究表明，磁铁矿颗粒大小不一。个别镁铁质岩脉的粒度较小，而在镁铁质边界，尺寸从小到大不等。长英质核具有大晶粒尺寸。SEM 数据显示了长英质岩心样品和单个镁铁质岩脉样品中的氧化溶解结构。在镁铁质边界样品中仅发现钛铁矿，无论是作为非面体晶粒还是薄层，解释为磁铁矿的强烈氧化溶出。在从单个镁铁质岩脉到长英质岩芯和镁铁质边界的样品中观察到的氧溶度增加表明原始岩浆之间存在不同程度的相互作用。研究的侵入体显示正常的磁性织物，具有近垂直磁性叶理（k1-k2 平面）和近水平 (k1) 线状。磁数据与构造场测量结果一致，表明在就位期间存在亚水平岩浆流。在堤坝南部发现的更大体积和大小的飞地与其向北的进驻相容。