Abstract The late- to post-collisional Cape Granite Suite (CGS), located in the ~560–520 Ma Pan-African Saldania Belt of south-western South Africa, comprises S-, I-, and A-type granites, mafic intrusive rocks, and pyroclastic rocks. The CGS formed during the closing of the Adamastor Ocean during the Neoproterozoic to Early-Cambrian, related to Gondwana construction. The S-type granites of the suite have received much attention concerning their petrogenesis and sources. The I-type granites, however, remain largely little studied. Whole rock geochemical and isotopic data are used to assess the petrogenesis and sources of the I-type Vredenburg Granite in the north-western Saldania Belt. The Vredenburg Granite is weakly peraluminous, ferroan, and calc-alkalic to alkali-calcic. Associated with the granite are weakly peraluminous, magnesian, and calc-alkalic magmatic enclaves (ME), of which two major varieties are present, a granodioritic variety (ME1) and a biotite- and plagioclase-rich variety (ME2). The former has a similar composition to the host granite, whereas the latter is more mafic and dioritic in nature. The eNd(t) values, Sm–Nd model ages and geochemical characteristics of the enclaves and host granite reflect melting of heterogeneous crustal sources of Mesoproterozoic-age. Biotite-, and subordinate amounts of amphibole-bearing rocks, dominantly metagreywackes and psammites, were the likely sources; minor amounts of basalts likely also played a role. These rock types are typical of a continental arc setting. Previously, the granites were interpreted to have formed by fractionation. However, such processes are incompatible with the full chemical variation displayed by the granites and enclaves. They exhibit positive linear trends between whole-rock major and trace elements vs. maficity (molar Fe + Mg), which can be best explained by entrainment of a peritectic assemblage comprising plagioclase, garnet, an Fe-Ti-oxide (ilmenite or Ti-magnetite) and, potentially, orthopyroxene. An amphibolitic source component may have contributed clinopyroxene and ilmenite, the former, along with plagioclase, contributing to the Ca content of the magma. These, and the co-entrainment of such accessory minerals as zircon, apatite and allanite, can largely explain the major-, minor- and trace-element variations found in the granites and enclaves. Fractional crystallisation may have acted as a minor compositional driver in the granites and enclaves, and then only at high SiO2 content.

中文翻译：

---

包晶组合夹带作为南非西北部泛非萨尔达尼亚带 I 型 Vredenburg 花岗岩的主要成分驱动因素：全岩化学视角

摘要 晚碰撞后海角花岗岩组 (CGS) 位于南非西南部~560-520 Ma 泛非萨尔达尼亚带，包括 S 型、I 型和 A 型花岗岩，镁铁质侵入岩岩石和火山碎屑岩。CGS 形成于新元古代至早寒武纪阿达马斯特洋闭合期间，与冈瓦纳古大陆的构造有关。该套组的S型花岗岩在成因和来源方面备受关注。然而，对 I 型花岗岩的研究仍然很少。全岩地球化学和同位素数据用于评估萨尔达尼亚带西北部 I 型 Vredenburg 花岗岩的成因和来源。Vredenburg 花岗岩为弱过铝质、铁质、钙碱性至碱钙质。与花岗岩有关的是弱过铝质、镁质、和钙碱性岩浆飞地（ME），其中存在两个主要品种，花岗闪长岩品种（ME1）和富含黑云母和斜长石的品种（ME2）。前者具有与主体花岗岩相似的成分，而后者在性质上更具镁铁质和闪长岩。飞地和寄主花岗岩的 eNd(t) 值、Sm-Nd 模型年龄和地球化学特征反映了中元古代非均质地壳来源的熔融。黑云母和次要数量的含角闪石的岩石，主要是变灰岩和砂岩，是可能的来源；少量玄武岩也可能发挥了作用。这些岩石类型是典型的大陆弧环境。以前，花岗岩被解释为是通过分馏形成的。然而，这种过程与花岗岩和飞地所显示的全部化学变化不相容。它们在全岩主要元素和微量元素与镁铁矿（摩尔 Fe + Mg）之间表现出正线性趋势，这可以通过夹带包含斜长石、石榴石、Fe-Ti-氧化物（钛铁矿或 Ti-磁铁矿）和可能的斜方辉石。角闪石源成分可能贡献了单斜辉石和钛铁矿，前者与斜长石一起贡献了岩浆的 Ca 含量。这些，以及诸如锆石、磷灰石和花岗岩等副矿物的共同夹带，可以在很大程度上解释在花岗岩和飞地中发现的主要、次要和微量元素的变化。部分结晶可能是花岗岩和飞地中的次要成分驱动因素，