Precambrian Research ( IF 3.8 ) Pub Date : 2021-02-26 , DOI: 10.1016/j.precamres.2020.106063 Luiza de Carvalho Mendes , Ticiano José Saraiva dos Santos , Nádia Borges Gomes
Western Gondwana resulted from the closure of the Pharusian-Goianides Ocean, a process that culminated in the formation of magmatic arcs, high and ultra-high-pressure (HP-UHP) belts, and sedimentary basins. These tectonic units occur in the NW part of the Borborema Province (Northeastern Brazil), which encloses the Neoproterozoic Santa Quitéria magmatic arc (SQMA). Metasedimentary rocks (sillimanite-, garnet- and biotite-bearing gneiss, quartzite, and schist) that constitute the Canindé Complex and the Independência Unit surround the western and eastern margins of this arc. According to A/CNK and N/K ratios and the Chemical Index of Alteration calculated for each rock type, the protolith of these rocks correspond to moderately weathered pelites, greywacke, and lithic-arenite. Trace element distributions (LILE, HFSE and REE) indicate that the Canindé Complex rocks are depleted in Sc, V, Cr, Co, Ni and LILE and are formed by mature and stable minerals such as quartz, muscovite and K-feldspar, similarly to passive margin sediments. In contrast, the Independência rocks present higher concentrations of transition trace elements, constituted by unstable-system minerals (iron-magnesium minerals) and immature sediments, typical of active margin settings. In general, these rocks present felsic-source components, with ample fractionation between LREE over HREE (LaN/YbN = 26.2 to 4.16) and with a slight to strong negative Eu anomaly (Eu/Eu* = 1.26 to 0.33). Isotopic Hf data identified a mixture of crustal- and mantle-derived sources. According to tectonic setting discrimination diagrams (Co-Th-Zr/10 and Sc-Th-Zr/10) and the concentrations of characteristic trace elements and ratios (e.g., Th, V, Co, La, Ce, LaN/YbN), these rocks were interpreted as being deposited in basins formed in active and passive margin settings associated with continental and intraoceanic arcs. U-Pb zircon data indicates source rocks from the Archean (3.0 to 2.6 Ga) to the Neoproterozoic (820 to 541 Ma). According to our results, the Canindé and Independência supracrustal rocks were deposited in basins affected by different tectonic regimes, controlled by the installation of the Santa Quitéria Magmatic Arc (SQMA), starting with a passive margin or intracratonic basins that evolved into an active margin setting on the western SQMA margin (Canindé Complex) and a predominantly passive margin setting on the eastern SQMA margin (Independência Unit), leading to the formation of forearc and backarc basins.
中文翻译:
巴西东北部圣基特里亚岩浆弧周围的准沉积岩的地球化学和物源:西贡多瓦纳的构造和古地理意义
冈瓦纳西部是Pharusian-Goianides海洋关闭的结果,该过程最终形成了岩浆弧,高压和超高压(HP-UHP)带以及沉积盆地。这些构造单元出现在Borborema省(巴西东北部)的西北部,该地区包围了新元古代的圣基特里亚岩浆弧(SQMA)。构成CanindéComplex和IndependênciaUnit的准沉积岩(硅线石,石榴石和黑云母片麻岩,石英岩和片岩)围绕着这条弧线的西边和东边。根据A / CNK和N / K比率以及每种岩石类型的化学变化指数计算,这些岩石的原石对应于中等风化的贝利特岩,格雷瓦克岩和石质亚砷酸盐。微量元素分布(LILE,HFSE和REE)表明CanindéComplex岩石中的Sc,V,Cr,Co,Ni和LILE贫化,并且由成熟,稳定的矿物(如石英,白云母和钾长石)形成,类似于被动缘沉积物。相比之下,Independência岩石呈现较高浓度的过渡痕量元素,这些元素由不稳定系统的矿物(铁镁矿物)和不成熟的沉积物(活跃的边缘环境典型特征)构成。通常,这些岩石具有长英质成分,在LREE和HREE(La 由不稳定系统的矿物质(铁镁矿物质)和不成熟的沉积物(活动边界设置的典型特征)组成。通常,这些岩石具有长英质成分,在LREE和HREE(La 由不稳定系统的矿物质(铁镁矿物质)和不成熟的沉积物(活动边界设置的典型特征)组成。通常,这些岩石具有长英质成分,在LREE和HREE(LaN / Yb N = 26.2至4.16),并具有轻微至强烈的负Eu异常(Eu / Eu * = 1.26至0.33)。同位素Hf数据确定了地壳和地幔来源的混合物。根据构造背景判别图(Co-Th-Zr / 10和Sc-Th-Zr / 10)以及特征微量元素的浓度和比率(例如, Th,V,Co,La,Ce,La N / Yb N),这些岩石被解释为沉积在与大陆弧和海洋内弧相关的主动和被动边缘环境中形成的盆地中。U-Pb锆石数据表明从太古代(3.0至2.6 Ga)到新元古代(820至541 Ma)的烃源岩。根据我们的结果,Canindé和Independência地壳上的岩石沉积在受不同构造体制影响的盆地中,受圣基塔里亚岩浆弧(SQMA)的安装控制,从被动边缘或克拉通盆地演化为活动边缘设置西部SQMA边缘(CanindéComplex)位于东部SQMA边缘(IndependentênciaUnit),主要是被动边缘,导致前陆盆地和后弧盆地的形成。