Abstract The study of magnetic fabrics and rock magnetic properties, together with geological and structural mapping, was carried out in a syenite pluton to investigate its shape and emplacement history. The Piquiri Syenite Massif (PSM) is an alkaline pluton which exhibits S >> L magmatic fabric and is interpreted to be part of the last Neoproterozoic post-collisional magmatic episodes in southernmost Brazil. Thermomagnetic curves, hysteresis data and coercivity spectra obtained from representative samples of different facies in the massif reveal that magnetic susceptibility is dominated by ferromagnetic minerals, especially magnetite. Magnetic fabric data were determined by using Anisotropy of Magnetic Susceptibility (AMS) and Anisotropy of Anhysteretic Remanence (AARM). Both fabrics are coaxial, and the parallelism of AMS and AARM tensors in more than 84 % of the sampled sites rules out the possibility of significant effects of Single Domain (SD) crystals. The magnetic foliation is concordant with the magmatic foliation field measurements, both parallel to pluton contacts, with high, inward dip angles. The magnetic lineation shows distinct but related behaviour from one facies to another. It is dominantly subvertical in the marginal facies rocks and plunges at moderate to shallow angles in the main facies. It is sub-horizontal in the quartz-syenites and plunges at shallow angles in the granitic rocks. Oxidizing conditions determined from the study of magnetic mineralogy leads to challenge former interpretation of in situ differentiation and crystallization and points to the multi-intrusive character of the pluton. Field relations such as fragments of marginal facies rocks found within the main facies rocks, which are in turn intruded by quartz-syenites, together with the general absence of contact metamorphism except near the marginal facies, lead to interpret that a sequence of magmatic pulses have built up the pluton. Thus, a first magmatic pulse may have heated the host rocks and resulted in the marginal facies which was followed by the next pulses to form the main facies and the quartz-rich varieties, therefore constructing the pluton from outside inwards.

中文翻译：

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新元古代皮基里正长岩地块（巴西最南端）的磁性织物：对 3D 几何形状和就位的影响

摘要 对一个正长岩体进行了磁性组构和岩石磁性研究，并结合地质和构造绘图，研究了其形状和侵位历史。Piquiri 正长岩地块 (PSM) 是一种碱性岩体，具有 S >> L 岩浆结构，被解释为巴西最南端最后一次新元古代后碰撞岩浆事件的一部分。从地块不同相代表性样品获得的热磁曲线、磁滞数据和矫顽力谱表明，磁化率以铁磁性矿物为主，尤其是磁铁矿。磁性织物数据通过使用磁化率各向异性 (AMS) 和非磁滞剩磁各向异性 (AARM) 确定。两种面料都是同轴的，并且超过 84% 的采样点中 AMS 和 AARM 张量的平行性排除了单域 (SD) 晶体显着影响的可能性。磁性叶理与岩浆叶理场测量一致，两者都平行于岩体接触，具有高的向内倾角。磁力线从一个相到另一个相显示出不同但相关的行为。它在边缘相岩石中以近垂直为主，在主相中以中等至浅的角度俯冲。它在石英正长岩中是亚水平的，在花岗岩中以浅角度俯冲。从磁性矿物学研究中确定的氧化条件对原位分异和结晶的先前解释提出了挑战，并指出了岩体的多重侵入特征。诸如在主要相岩石中发现的边缘相岩石碎片，这些碎片又被石英正长岩侵入，以及除了边缘相附近一般没有接触变质作用，导致解释一系列岩浆脉冲具有建立了岩体。因此，第一个岩浆脉冲可能加热了主岩并产生了边缘相，随后的脉冲形成了主要相和富含石英的品种，因此从外向内构造了岩体。