The Tectono-Metamorphic Evolution of the Namaqua Metamorphic Province

Dear colleagues

The Namaqua Metamorphic Province (NMP) in Southern Africa is one of the largest Mesoproterozoic metamorphic belts on Earth, with prolonged and intense magmatic and metamorphic episodes between ~1300 and 950 Ma. Large parts of the NMP consist of granites, most of which were emplaced between ~1230 and 1100 Ma into hot middle continental crust, part of which reaches ultrahigh-temperature conditions at pressures not exceeding ~500 MPa. Typically, the metamorphic peaks are followed by near-isobaric P–T paths. Intense, commonly contractional deformation has taken place in several tectonic episodes. The Namaqua Sector exposed in western South Africa and Southern Namibia, and the Natal Sector in southeastern South Africa, developed at roughly the same time but according to the available data appear to be different from each other in some possibly significant respects, particularly with regard to the abundance of Palaeoproterozoic heritage and the tectonic position and setting in Mesoproterozoic time. Further, the mineral endowment differs, with several significant ore deposits or occurrences in the Namaqua Sector (base metal, lithium, REE) but much less mineralization in the Natal Sector.

The traditional literature over the last four decades has mostly seen this history in the context of the Grenvillian orogeny and the assembly of the Rodinia supercontinent, postulating the amalgamation of continental fragments that in the early and mid-Mesoproterozoic were separated by several oceanic basins. Increasing evidence, however, suggests widespread and uniform Palaeoproterozoic lithospheric heritage in all parts of the NMP, which show similarity with those domains of the belt that have formed in Paleoproterozoic time and remained largely unaffected by tectonic, metamorphic, and magmatic episodes in Mesoproterozoic time.

In recent decades, the database for the NMP has steadily grown, particularly with regard to geochronological data. However, this has not necessarily improved the overall understanding of regional crustal evolution, nor has it confirmed the traditional tectonic models in which the NMP is supposed to have formed. In some instances, new data were fitted into the traditional model, even where they do not appear to support, or even may contradict it, rather than seeking new avenues of data interpretation.

In this Special Issue, we invite original or review papers that provide new perspectives on the tectonometamorphic evolution of the Namaqua Metamorphic Province. Such papers may be based on new data, re-interpret published data, or present reviews on existing data sets that provide key insight into crustal evolution.

The Special Issue will include publications on the following topics:

• The timing and conditions of regional tectonic episodes;
• The nature and significance of domain boundaries in the NMP;
• The abundance and sources of granitoid and mafic magmatism over time and space in the NMP;
• The formation episodes of the juvenile Mesoproterozoic crust and Paleoproterozoic precursors;
• The relationships between Paleoproterozoic crustal entities in the Richtersveld, the Sperrgebiet, and the Kheis with each other and with Mesoproterozoic domains;
• Studies on the metamorphic evolution and the critical assessments of the metamorphic evolution in relation to tectonic processes and settings;
• The differences and commonalities between crustal evolution in the Namaqua Sector and the Natal Belt;
• The deposition and tectonic setting of sedimentary rocks in the NMP in Mesoproterozoic time;
• The context of ore forming processes and the regional tectonometamorphic evolution of the NMP.

Dr. Steffen Büttner
Dr. Russell Bailie
Guest Editors

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• Mesoproterozoic crustal evolution
• Paleoproterozoic heritage
• magma sources
• tectonic settings
• P–T–t–d paths
• southern Africa
• Rodinia
• continental back-arc vs. collisional models