Geology, petrology, U-Pb (shrimp) geochronology of the Morrinhos granite -Paraguá terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignácio orogeny

Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km2 long; it is located in the municipality of Vila Bela da Santíssima Trindade of the state of Mato Grosso, Brazil, in the Paraguá Terrane, Rondonian-San Ignácio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the greenschist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S1) and open folds (D2), and both phases were most likely related to the San Ignácio Orogeny. The geochronological (U-Pb SHRIMP) and isotopic (Sm-Nd) investigations of these rocks indicated a crystallization age of 1350 ± 12 Ma, TDMof approximately 1.77 Ga and εNd(1.35)with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian) continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignácio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite.莫里纽斯花岗岩（Morrinhos granite）为一呈北北西（NNW）方向轻微延展的岩基体，出露面积约1140 km²；其坐落于巴西马托格罗索州圣三一维拉贝拉（Vila Bela da Santíssima Trindade）市镇，地处亚马孙克拉通（Amazonian Craton）西南部的隆多尼亚-圣伊纳西构造省（Rondonian-San Ignácio Province）内的巴拉圭地体（Paraguá Terrane）中。该侵入体的岩石成分从英云闪长岩（tonalite）至二长花岗岩（monzogranite）均有分布，具有中粗粒不等粒结构，局部发育斑状构造；其中一个岩相以黑云母为主要铁镁矿物，另一岩相则以角闪石为主，二者均变质至绿片岩相（greenschist facies）。本次研究的岩石属于一套由亚碱性岩浆作用（subalkaline magmatism）形成的中酸性岩系；该岩系的地球化学属性为碱钙性-准铝质-弱过铝质，岩石演化以分离结晶（fractioned crystallization）机制为主。构造数据揭示存在两期变形作用，分别以透入性面理（S1）和开阔褶皱（D2）为典型标志，且这两期变形均大概率与圣伊纳西造山运动（San Ignácio Orogeny）相关。对这些岩石开展的地质年代学（U-Pb SHRIMP）与同位素（Sm-Nd）研究结果表明，其结晶年龄为1350 ± 12 Ma，地壳模式年龄（TDM）约为1.77 Ga，εNd(1.35)值为-2.57的负值，指示其形成与古元古代（斯泰特纪，Statherian）大陆地壳的部分熔融作用有关。本次研究结果显示，莫里纽斯花岗岩形成于圣伊纳西造山运动造山晚期至造山后阶段的大陆岩浆弧环境中，可归属于彭西亚托侵入岩套（Pensamiento Intrusive Suite）。