The Karagwe-Ankole belt (KAB) is a poorly understood deformation belt in the Great Lakes area of Central Africa, with several hypotheses put forward to explain the emplacement of the various generations of granites. The youngest generation of granites (G4; 1000 Ma) are spatially associated with Sn-W-Ta ore deposits, and are considered as the parental granites. The paragenesis of these mineral resources have been extensively scrutinised, but the geodynamic context and characterisation of these parental granites has been neglected. Tectonic models for the formation of this plutonic suite range from an intra-cratonic to full-scale continent–continent collision setting.

In this study, the G4 intrusive suite of the KAB granites, are characterised based on whole-rock geochemical analysis and U-Pb zircon dating.

Two main populations of U-Pb zircon ages are identified in the G4 granites at 1370–1420 Ma and 950–1020 Ma. The older population is attributed to inheritance of the bimodal magmatic Kibaran event, while the younger population is ascribed to the new crystallisation. G4 granites contain xenocrystic zircon, indicating inheritance of older granites or basement rocks. G4 granites are, however, much more differentiated compared to older Kibaran granites, containing higher K and Rb and lower Ca, Sr and Ba concentrations, which implicates recycling of older crustal material. The variable geochemistry, as well as the different proportions of xenocrystic zircons in the different granite bodies, suggest melting was highly localised and derived from a highly heterogeneous source region, for which an intracontinental setting is favoured. The Th/U ratios of the parental granites are lower than 0.1, which would suggest a metamorphic origin of the granites. Together with the low luminescence signal of these zircons an anatectic origin of the melt is considered, implying that the parental granites could be considered more like migmatites rather than actual granites formed by fractionation out of large magma chambers.

在中非大湖地区，Karagwe-Ankole带（KAB）是一个鲜为人知的形变带，提出了几种假说来解释各代花岗岩的位置。最年轻的花岗岩（G4； 1000 Ma）在空间上与Sn-W-Ta矿床有关，被认为是母体花岗岩。这些矿物资源的共生性已被广泛研究，但这些亲代花岗岩的地球动力学背景和特征却被忽略了。形成这种岩性套件的构造模型范围从克拉通内到全面的大陆—大陆碰撞背景。

在这项研究中，基于全岩石地球化学分析和U-Pb锆石测年对G4侵入岩组的KAB花岗岩进行了表征。

在G4花岗岩中，在1370–1420 Ma和950–1020 Ma处确定了两个主要的U-Pb锆石年龄。老年人群归因于双峰岩浆基巴拉事件的遗传，而年轻人群归因于新的结晶。G4花岗岩含有异晶锆石，表明较老的花岗岩或基底岩石具有继承性。然而，G4花岗岩与较旧的Kibaran花岗岩相比，差异更大，其含有较高的K和Rb以及较低的Ca，Sr和Ba浓度，这意味着要回收较旧的地壳物质。可变的地球化学，以及不同花岗岩体中异晶锆石的不同比例，表明融化高度局部化，并且源自高度异质的源区，因此有利于陆内环境。亲本花岗岩的Th / U比值低于0.1，这暗示了花岗岩的变质成因。连同这些锆石的低发光信号一起，考虑到了熔体的麻醉成因，这意味着可以将母体花岗岩更像是辉锰矿，而不是通过在大型岩浆室内分馏而形成的实际花岗岩。