Earth Science Frontiers ›› 2024, Vol. 31 ›› Issue (4): 237-257.DOI: 10.13745/j.esf.sf.2024.2.15

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Petrogenesis of Paleoproterozoic granites in the Dondo area, northern Angola block: Geological response to the assembly of Columbia Supercontinent

LIU Wei1,2(), ZHANG Hongrui3,*(), LUO Dike3, JIA Pengfei3, JIN Lijie1,2, ZHOU Yonggang1, LIANG Yunhan1, WANG Zisheng1, LI Chunjia1   

  1. 1. No.1 Geological Team of Shandong Provincial Bereau of Geology and Mineral Resources, Jinan 250014, China
    2. Shandong Engineering Research Center of High-grade Iron Deposits Exploration and Exploitation, Jinan 250014, China
    3. Citic Construction Co., Ltd., Beijing 100027, China
  • Received:2023-06-25 Revised:2024-01-16 Online:2024-07-25 Published:2024-07-10

Abstract:

The Paleoproterozoic Eburnean orogenic granites are widely exposed in the western part of Angola, offering an ideal setting to study the magmatism and tectonic evolution of the Angola Block. This paper presents systematic studies of petrology, petrogeochemistry, and zircon U-Pb geochronology on the exposed granites in the Dondo area, northern Angola Block. The results indicate that the emplacement ages of porphyritic biotite monzonite granite and biotite monzonite granite in the Dondo area are 1983.3±7.7 Ma and 1956.6±7.5 Ma, respectively, both products of middle Paleoproterozoic magmatic activity. The whole-rock samples are characterized by high SiO2, ALK, 10000Ga/Al, FeOT/(FeOT+MgO), and Zr+Y+Nb+Ce, and low MgO, TiO2, CaO, and P2O5. Trace elements are enriched in Rb, K, Th, U, Zr, and Hf, and depleted in Sr, Nb, Ta, P, and Ti. All samples are enriched in LREE and depleted in HREE, with no significant negative Eu anomaly. The crystallization temperature, calculated using zircon saturation thermometry, ranges from 757 to 889 ℃. Based on these geochemical characteristics, the granites in the Dondo area are classified as A2-type granite. Mineralogical and geochemical features suggest that the porphyritic biotite monzonite granite and biotite monzonite granite were generated by the mixing of crust-derived melts and mantle-derived mafic magma. The similar formation ages within analytical error, identical mineral assemblages, and consistent variations in major and trace elemental compositions indicate that their parental magma originated from a common magma chamber, with lithological differences resulting from melt extraction processes. It is proposed that the magma producing the potassium feldspar porphyry resided in the deep crust for an extended period, leading to stable crystallization of potassium feldspar, increased viscosity and density, and a frozen state of the magma. Subsequent thermal disturbance and volatile enrichment from mantle-derived magma injection rapidly reactivated the frozen magma chamber, resulting in crystal-melt separation. The extracted melt formed biotite monzonite granite, while magma mixed with pre-existing crystals formed porphyritic biotite monzonite granite. Combining regional and global tectonic evolution, it is suggested that the granites from the Dondo area formed in a post-collision tectonic environment between the São Francisco Craton and the Congo Craton. The Paleoproterozoic magmatic events in the Angola Block are likely responses to the Columbia Supercontinent assembly.

Key words: Angola Block, Paleoproterozoic, petrogenesis, A-type granites, remobilizing mechanism of frozen magma chambers, Columbia Supercontinent

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