A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain

P. H. Macey; R. J. Thomas; A. F.M. Kisters; J. F.A. Diener; M. Angombe; S. Doggart; C. A. Groenewald; C. W. Lambert; J. A. Miller; H. Minnaar; H. Smith; H. F.G. Moen; E. Muvangua; A. Nguno; G. Shifotoka; J. Indongo; D. Frei; C. Spencer; P. le Roux; R. A. Armstrong; C. Tinguely

doi:10.1016/j.gsf.2022.101408

A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain

P. H. Macey, R. J. Thomas^*, A. F.M. Kisters, J. F.A. Diener, M. Angombe, S. Doggart, C. A. Groenewald, C. W. Lambert, J. A. Miller, H. Minnaar, H. Smith, H. F.G. Moen, E. Muvangua, A. Nguno, G. Shifotoka, J. Indongo, D. Frei, C. Spencer, P. le Roux, R. A. ArmstrongC. Tinguely

^*Corresponding author for this work

Geochemistry

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Abstract

A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ∼1350 Ma to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the Archaean Craton. In eastern Namaqualand, early rift-related magmatism and sedimentation at ∼1350 Ma occurred in a confined ocean basin. Subsequent tectonic reversal and subduction at ∼1290–1240 Ma led to establishment of the Areachap, Konkiep and Kaaien Domains. In the Kakamas Domain, widespread deposition of pelitic sediments occurred at ~1220 Ma (Narries Group). These contain detrital zircons derived from proximal crust with ages between ∼2020 Ma and 1800 Ma (western Palaeoproterozoic domains) and 1350–1240 Ma (eastern early Namaqua domains), suggesting pre-sedimentation juxtaposition. The pelites underwent granulite grade metamorphism at ∼1210 Ma (peak conditions: 4.5–6 kbar and 770–850 °C), associated with voluminous, predominantly S-type granitoid orthogneisses between ∼1210 Ma and 1190 Ma (Eendoorn and Ham River Suites) and low-angle ductile (D₂) deformation which continued until ∼1110 Ma, interspersed with periods of sedimentation. This enduring P-T regime is inconsistent with the expected crustal over-thickening associated with the generally-accepted collision-accretion Namaqualand model. Rather, we propose the Namaqua Sector is a ‘hot orogen’ developed in a wide continental back-arc with subduction west of the present-day outcrop. The observed high geotherm resulted from thinned back-arc lithosphere accompanied by an influx of mantle-derived melts. Ductile D₂ deformation resulted from “bottom-driven” tectonics and viscous drag within the crust by convective flow in the underlying asthenospheric mantle. This extended tectonothermal regime ceased at ∼1110 Ma when SW-directed thrusting stacked the Namaqua Domains into their current positions, constrained in the Kakamas Domain by late- to post-tectonic I-type granitoids intruded between ∼1125 Ma and 1100 Ma (Komsberg Suite). The thermal peak then shifted west to the Bushmanland and Aus Domains, where voluminous granites (1080–1025 Ma) were associated with high-T/low-P granulite facies thermal metamorphism and mega-scale open folding (D₃). Unroofing of the Namaqua Sector is marked by large-scale, NW-trending, sub-vertical transcurrent dextral shear zones and associated pegmatites and leucogranites at ∼990 Ma.

Original language	English
Article number	101408
Journal	Geoscience Frontiers
Volume	13
Issue number	4
DOIs	https://doi.org/10.1016/j.gsf.2022.101408
Publication status	Published - Jul 2022

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Macey, P. H., Thomas, R. J., Kisters, A. F. M., Diener, J. F. A., Angombe, M., Doggart, S., Groenewald, C. A., Lambert, C. W., Miller, J. A., Minnaar, H., Smith, H., Moen, H. F. G., Muvangua, E., Nguno, A., Shifotoka, G., Indongo, J., Frei, D., Spencer, C., le Roux, P., ... Tinguely, C. (2022). A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain. Geoscience Frontiers, 13(4), Article 101408. https://doi.org/10.1016/j.gsf.2022.101408

@article{27d8df15edec4fd29ed2cdb15f1a9fd6,

title = "A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain",

abstract = "A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ∼1350 Ma to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the Archaean Craton. In eastern Namaqualand, early rift-related magmatism and sedimentation at ∼1350 Ma occurred in a confined ocean basin. Subsequent tectonic reversal and subduction at ∼1290–1240 Ma led to establishment of the Areachap, Konkiep and Kaaien Domains. In the Kakamas Domain, widespread deposition of pelitic sediments occurred at ~1220 Ma (Narries Group). These contain detrital zircons derived from proximal crust with ages between ∼2020 Ma and 1800 Ma (western Palaeoproterozoic domains) and 1350–1240 Ma (eastern early Namaqua domains), suggesting pre-sedimentation juxtaposition. The pelites underwent granulite grade metamorphism at ∼1210 Ma (peak conditions: 4.5–6 kbar and 770–850 °C), associated with voluminous, predominantly S-type granitoid orthogneisses between ∼1210 Ma and 1190 Ma (Eendoorn and Ham River Suites) and low-angle ductile (D2) deformation which continued until ∼1110 Ma, interspersed with periods of sedimentation. This enduring P-T regime is inconsistent with the expected crustal over-thickening associated with the generally-accepted collision-accretion Namaqualand model. Rather, we propose the Namaqua Sector is a {\textquoteleft}hot orogen{\textquoteright} developed in a wide continental back-arc with subduction west of the present-day outcrop. The observed high geotherm resulted from thinned back-arc lithosphere accompanied by an influx of mantle-derived melts. Ductile D2 deformation resulted from “bottom-driven” tectonics and viscous drag within the crust by convective flow in the underlying asthenospheric mantle. This extended tectonothermal regime ceased at ∼1110 Ma when SW-directed thrusting stacked the Namaqua Domains into their current positions, constrained in the Kakamas Domain by late- to post-tectonic I-type granitoids intruded between ∼1125 Ma and 1100 Ma (Komsberg Suite). The thermal peak then shifted west to the Bushmanland and Aus Domains, where voluminous granites (1080–1025 Ma) were associated with high-T/low-P granulite facies thermal metamorphism and mega-scale open folding (D3). Unroofing of the Namaqua Sector is marked by large-scale, NW-trending, sub-vertical transcurrent dextral shear zones and associated pegmatites and leucogranites at ∼990 Ma.",

keywords = "Geochronology, Geodynamics, Hot orogeny, Kakamas, Mesoproterozoic, Namaqua",

author = "Macey, {P. H.} and Thomas, {R. J.} and Kisters, {A. F.M.} and Diener, {J. F.A.} and M. Angombe and S. Doggart and Groenewald, {C. A.} and Lambert, {C. W.} and Miller, {J. A.} and H. Minnaar and H. Smith and Moen, {H. F.G.} and E. Muvangua and A. Nguno and G. Shifotoka and J. Indongo and D. Frei and C. Spencer and {le Roux}, P. and Armstrong, {R. A.} and C. Tinguely",

note = "Publisher Copyright: {\textcopyright} 2022 China University of Geosciences (Beijing) and Peking University",

year = "2022",

month = jul,

doi = "10.1016/j.gsf.2022.101408",

language = "English",

volume = "13",

journal = "Geoscience Frontiers",

issn = "1674-9871",

publisher = "Elsevier B.V.",

number = "4",

}

Macey, PH, Thomas, RJ, Kisters, AFM, Diener, JFA, Angombe, M, Doggart, S, Groenewald, CA, Lambert, CW, Miller, JA, Minnaar, H, Smith, H, Moen, HFG, Muvangua, E, Nguno, A, Shifotoka, G, Indongo, J, Frei, D, Spencer, C, le Roux, P, Armstrong, RA & Tinguely, C 2022, 'A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain', Geoscience Frontiers, vol. 13, no. 4, 101408. https://doi.org/10.1016/j.gsf.2022.101408

TY - JOUR

T1 - A continental back-arc setting for the Namaqua belt

T2 - Evidence from the Kakamas Domain

AU - Macey, P. H.

AU - Thomas, R. J.

AU - Kisters, A. F.M.

AU - Diener, J. F.A.

AU - Angombe, M.

AU - Doggart, S.

AU - Groenewald, C. A.

AU - Lambert, C. W.

AU - Miller, J. A.

AU - Minnaar, H.

AU - Smith, H.

AU - Moen, H. F.G.

AU - Muvangua, E.

AU - Nguno, A.

AU - Shifotoka, G.

AU - Indongo, J.

AU - Frei, D.

AU - Spencer, C.

AU - le Roux, P.

AU - Armstrong, R. A.

AU - Tinguely, C.

PY - 2022/7

Y1 - 2022/7

N2 - A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ∼1350 Ma to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the Archaean Craton. In eastern Namaqualand, early rift-related magmatism and sedimentation at ∼1350 Ma occurred in a confined ocean basin. Subsequent tectonic reversal and subduction at ∼1290–1240 Ma led to establishment of the Areachap, Konkiep and Kaaien Domains. In the Kakamas Domain, widespread deposition of pelitic sediments occurred at ~1220 Ma (Narries Group). These contain detrital zircons derived from proximal crust with ages between ∼2020 Ma and 1800 Ma (western Palaeoproterozoic domains) and 1350–1240 Ma (eastern early Namaqua domains), suggesting pre-sedimentation juxtaposition. The pelites underwent granulite grade metamorphism at ∼1210 Ma (peak conditions: 4.5–6 kbar and 770–850 °C), associated with voluminous, predominantly S-type granitoid orthogneisses between ∼1210 Ma and 1190 Ma (Eendoorn and Ham River Suites) and low-angle ductile (D2) deformation which continued until ∼1110 Ma, interspersed with periods of sedimentation. This enduring P-T regime is inconsistent with the expected crustal over-thickening associated with the generally-accepted collision-accretion Namaqualand model. Rather, we propose the Namaqua Sector is a ‘hot orogen’ developed in a wide continental back-arc with subduction west of the present-day outcrop. The observed high geotherm resulted from thinned back-arc lithosphere accompanied by an influx of mantle-derived melts. Ductile D2 deformation resulted from “bottom-driven” tectonics and viscous drag within the crust by convective flow in the underlying asthenospheric mantle. This extended tectonothermal regime ceased at ∼1110 Ma when SW-directed thrusting stacked the Namaqua Domains into their current positions, constrained in the Kakamas Domain by late- to post-tectonic I-type granitoids intruded between ∼1125 Ma and 1100 Ma (Komsberg Suite). The thermal peak then shifted west to the Bushmanland and Aus Domains, where voluminous granites (1080–1025 Ma) were associated with high-T/low-P granulite facies thermal metamorphism and mega-scale open folding (D3). Unroofing of the Namaqua Sector is marked by large-scale, NW-trending, sub-vertical transcurrent dextral shear zones and associated pegmatites and leucogranites at ∼990 Ma.

AB - A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ∼1350 Ma to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the Archaean Craton. In eastern Namaqualand, early rift-related magmatism and sedimentation at ∼1350 Ma occurred in a confined ocean basin. Subsequent tectonic reversal and subduction at ∼1290–1240 Ma led to establishment of the Areachap, Konkiep and Kaaien Domains. In the Kakamas Domain, widespread deposition of pelitic sediments occurred at ~1220 Ma (Narries Group). These contain detrital zircons derived from proximal crust with ages between ∼2020 Ma and 1800 Ma (western Palaeoproterozoic domains) and 1350–1240 Ma (eastern early Namaqua domains), suggesting pre-sedimentation juxtaposition. The pelites underwent granulite grade metamorphism at ∼1210 Ma (peak conditions: 4.5–6 kbar and 770–850 °C), associated with voluminous, predominantly S-type granitoid orthogneisses between ∼1210 Ma and 1190 Ma (Eendoorn and Ham River Suites) and low-angle ductile (D2) deformation which continued until ∼1110 Ma, interspersed with periods of sedimentation. This enduring P-T regime is inconsistent with the expected crustal over-thickening associated with the generally-accepted collision-accretion Namaqualand model. Rather, we propose the Namaqua Sector is a ‘hot orogen’ developed in a wide continental back-arc with subduction west of the present-day outcrop. The observed high geotherm resulted from thinned back-arc lithosphere accompanied by an influx of mantle-derived melts. Ductile D2 deformation resulted from “bottom-driven” tectonics and viscous drag within the crust by convective flow in the underlying asthenospheric mantle. This extended tectonothermal regime ceased at ∼1110 Ma when SW-directed thrusting stacked the Namaqua Domains into their current positions, constrained in the Kakamas Domain by late- to post-tectonic I-type granitoids intruded between ∼1125 Ma and 1100 Ma (Komsberg Suite). The thermal peak then shifted west to the Bushmanland and Aus Domains, where voluminous granites (1080–1025 Ma) were associated with high-T/low-P granulite facies thermal metamorphism and mega-scale open folding (D3). Unroofing of the Namaqua Sector is marked by large-scale, NW-trending, sub-vertical transcurrent dextral shear zones and associated pegmatites and leucogranites at ∼990 Ma.

KW - Geochronology

KW - Geodynamics

KW - Hot orogeny

KW - Kakamas

KW - Mesoproterozoic

KW - Namaqua

UR - http://www.scopus.com/inward/record.url?scp=85131918310&partnerID=8YFLogxK

U2 - 10.1016/j.gsf.2022.101408

DO - 10.1016/j.gsf.2022.101408

M3 - Article

SN - 1674-9871

VL - 13

JO - Geoscience Frontiers

JF - Geoscience Frontiers

IS - 4

M1 - 101408

ER -

A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain

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