TY - JOUR
T1 - Reconnaissance geochronology, tectonothermal evolution, and regional significance of the middle proterozoic choma-kalomo block, Southern Zambia
AU - Hanson, Richard E.
AU - Wilson, Terry J.
AU - Brueckner, Hannes K.
AU - Onstott, Tullis C.
AU - Wardlaw, Melissa S.
AU - Johns, Chris C.
AU - Hardcastle, Kenneth C.
N1 - Funding Information:
This research was supported by National Science Foundation INT grant 82-14234 to Brueckner and I.W.D. Dalziel, by University of Zambia research grants E71-18-939 and E71-18-940 to Hanson, Wilson, and Onstott, and by an Ohio State University Seed Grant award to Wilson. We thank G.H. Girty, San Diego State University, for discussions regarding interpretation of the U-Pb zircon data, and N. Money, Director of the Geological Survey of Zambia, for access to unpublished survey material. H. Munyanyiwa, School of Mines, University of Zambia, and B. Mapani, Geological Survey of Zambia, assisted greatly in the field work described herein. We are indebted to Dr. E.H. Jere, Dean of the School of Mines, Prof. D.C. Turner, previous head of the Geology Department, and Prof. M. Wendorff, present head of the Geology Department, University of Zambia, for their support during the field work. We also thank R. Heald, manager of Demu Ranch, and J. Maluba, manager of Florida Ranch, Zambezi Ranching Corporation, tbr access to parts of the Semahwa River area. Comments by M.C. Daly and two anonymous reviewers greatly improved the manuscript. Lamont-Doherty Geological Observatory Contribution no. 4343.
PY - 1988/11
Y1 - 1988/11
N2 - New U-Pb zircon, 40Ar-39Ar, Rb-Sr and Sm-Nd data provide the first numerical chronology for the tectonothermal evolution of the Choma-Kalomo block, an extensive Middle Proterozoic terrane in southern Zambia to the south of the Pan-African Zambezi belt. The Choma-Kalomo batholith, a large plutonic body in the central part of the block, is shown to be a composite intrusion emplaced from c. 1345 to 1200 Ma, based on U-Pb zircon ages and detailed mapping of intrusive relations. Early phases of the batholith were intruded as syntectonic to late-syntectonic plutons during development of a penetrative S1 fabric in the metasedimentary country rocks of the Choma-Kalomo block. D2 folding produced the regional NE-SW structural trends in the block and possibly occurred at c. 1230 Ma, based on an Rb-Sr isochron from an early phase of the batholith containing a penetrative S2 foliation. An U-Pb zircon age of c. 1200 Ma from post-tectonic granite provides a younger limit to the timing of D2. 40Ar-39Ar mineral ages from the posttectonic granite, and Sm-Nd and 40Ar-39Ar mineral ages from amphibolites in country-rock paragneisses, range from c. 1200 to 500 Ma, recording post-D2 cooling followed by subsequent low-grade Pan-African overprinting along the southern margin of the Zambezi belt. D1 in the Choma-Kalomo block at c. 1345 Ma is substantially younger than Early Proterozoic orogenesis in adjacent terranes to the east in Zimbabwe, indicating that a major Precambrian discontinuity beneath the mid-Zambezi Valley separates these regions. D1 in the block is similar in age to plutonic and deformational events dated at c. 1350-1400 Ma in the Irumide belt of central and northern Zambia, suggesting that these two terranes on each side of the younger, cross-cutting Zambezi belt are parts of a single, originally continuous Middle Proterozoic mobile belt. Continuity between the Choma-Kalomo block and broadly coeval terranes to the southwest in Namibia and South Africa also appears likely, and all of these areas are considered to form parts of a Middle Proterozoic orogenic province lying west of the Kaapvaal and Zimbabwe cratons.
AB - New U-Pb zircon, 40Ar-39Ar, Rb-Sr and Sm-Nd data provide the first numerical chronology for the tectonothermal evolution of the Choma-Kalomo block, an extensive Middle Proterozoic terrane in southern Zambia to the south of the Pan-African Zambezi belt. The Choma-Kalomo batholith, a large plutonic body in the central part of the block, is shown to be a composite intrusion emplaced from c. 1345 to 1200 Ma, based on U-Pb zircon ages and detailed mapping of intrusive relations. Early phases of the batholith were intruded as syntectonic to late-syntectonic plutons during development of a penetrative S1 fabric in the metasedimentary country rocks of the Choma-Kalomo block. D2 folding produced the regional NE-SW structural trends in the block and possibly occurred at c. 1230 Ma, based on an Rb-Sr isochron from an early phase of the batholith containing a penetrative S2 foliation. An U-Pb zircon age of c. 1200 Ma from post-tectonic granite provides a younger limit to the timing of D2. 40Ar-39Ar mineral ages from the posttectonic granite, and Sm-Nd and 40Ar-39Ar mineral ages from amphibolites in country-rock paragneisses, range from c. 1200 to 500 Ma, recording post-D2 cooling followed by subsequent low-grade Pan-African overprinting along the southern margin of the Zambezi belt. D1 in the Choma-Kalomo block at c. 1345 Ma is substantially younger than Early Proterozoic orogenesis in adjacent terranes to the east in Zimbabwe, indicating that a major Precambrian discontinuity beneath the mid-Zambezi Valley separates these regions. D1 in the block is similar in age to plutonic and deformational events dated at c. 1350-1400 Ma in the Irumide belt of central and northern Zambia, suggesting that these two terranes on each side of the younger, cross-cutting Zambezi belt are parts of a single, originally continuous Middle Proterozoic mobile belt. Continuity between the Choma-Kalomo block and broadly coeval terranes to the southwest in Namibia and South Africa also appears likely, and all of these areas are considered to form parts of a Middle Proterozoic orogenic province lying west of the Kaapvaal and Zimbabwe cratons.
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U2 - 10.1016/0301-9268(88)90009-5
DO - 10.1016/0301-9268(88)90009-5
M3 - Article
AN - SCOPUS:0024257340
SN - 0301-9268
VL - 42
SP - 39
EP - 61
JO - Precambrian Research
JF - Precambrian Research
IS - 1-2
ER -