Depositional environments and an apparent age for the Geci meta-limestones: Constraints on the geological history of northern Mozambique

Melezhik, Victor A.; Кузнецов, А. Б.; Fallick, Anthony E.; Smith, Richard A.; Горохов, И. М.; Jamal, D.; Catuane, F.

doi:10.1016/j.precamres.2006.03.003

Cited by 38 publications

(22 citation statements)

References 37 publications

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“…The new mapping (Norconsult, 2007a, b), supported by geochemical data (Appendix), chemostratigraphic data (Melezhik et al, 2006; and some 60 U-Pb zircon or monazite age determinations (Kröner et al, 1997;Engvik et al, 2007;Jacobs et al, 2008;Viola et al, 2008;Bjerkgård et al, 2009;Bingen et al, 2009) leads to an improved, and quite different regional interpretation.…”

Section: Geochemical Signatures and Geological Evolutionmentioning

confidence: 73%

“…Although contacts between the Geci rocks and the granulite complexes are not exposed, the sharp discordance in metamorphic grade indicates that the contacts are tectonic. In places, primary depositional features are well preserved (Melezhik et al, 2006). The dominant rocks are calcarenites, dolarenites, calcite matrix-supported and dolostone clast-supported carbonate breccias forming beds with erosional bases, normal and reverse graded bedding, and welldeveloped Bouma sequences.…”

Section: Geci Groupmentioning

confidence: 98%

“…Dolomicritic, microbial and oolitic dolostone clasts were apparently derived from the margin of a shallow-water carbonate platform and redeposited by turbidity currents on a continental slope with calcareous sedimentation. A chemostratigraphic study by Melezhik et al (2006) showed that the least-altered 87 Sr/ 86 Sr and ␦ 13 C ratios suggest an apparent depositional age of either 590 to 585 or 630 to 625 Ma. This provides a lower age limit for juxtaposition of the low-grade Geci Group rocks and granulite-facies rocks of the Unango Complex.…”

Section: Geci Groupmentioning

confidence: 99%

“…The samples were collected in order to characterize the major and trace element composition of exposed rock units, and not to support process-oriented geochemical research. Structural, geochronological and other thematic data are published elsewhere (Engvik et al, 2007;Melezhik et al, 2006;Viola et al, 2008;Bingen et al, 2009;Bjerkgård et al, 2009). These articles represent an integral part of our study and were fundamental in proposing the model discussed: the reader is referred to those publications for more details.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The Geology and Geochemistry of the East African Orogen in Northeastern Mozambique

Boyd

Nordgulen

Thomas

et al. 2010

South African Journal of Geology

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Section: Geochemical Signatures and Geological Evolutionmentioning

confidence: 73%

Section: Geci Groupmentioning

confidence: 98%

Section: Geci Groupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Geology and Geochemistry of the East African Orogen in Northeastern Mozambique

Boyd

Nordgulen

Thomas

et al. 2010

South African Journal of Geology

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“…In the northwest of the Unango Complex, extensive arrays of anastomosing shear zones (e.g., the Macaloge Shear Zone; Bingen et al 2009) connect with the Chilwa-Mavago Corridor and contain slivers of ca. 600 Ma metasedimentary rocks of marine affinity (Cobue and Geci Groups: Melezhik et al 2006;Boyd et al 2010). In the southwest, the southern basement is dissected by the Namama Belt (Cadoppi et al 1987), a sinistral, steep, probably postcollisional shear zone (Macey et al 2010).…”

Section: Geological Backgroundmentioning

confidence: 99%

Postcollisional High-Grade Metamorphism, Orogenic Collapse, and Differential Cooling of the East African Orogen of Northeast Mozambique

Ueda

Jacobs²,

Thomas³

et al. 2012

The Journal of Geology

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A B S T R A C TThe postcollisional tectonic development of northeast Mozambique and subsequent cooling from high-temperature metamorphism is delineated with an extensive new set of U-Pb titanite, 40 Ar/ 39 Ar hornblende, and 40 Ar/ 39 Ar mica analyses. The complex data suggest a polyphase metamorphic history from the late Neoproterozoic to the Ordovician within the East African-Antarctic Orogen (EAAO), with marked differences between the major constituent blocks. In all the data sets, samples from the basement south of the Lú rio Belt show generally younger ages than those from the north, resulting from a late metamorphic event and slow cooling between ca. 520 and 440 Ma. The ages north and south of the Lú rio Belt are consistently offset by ca. 30-70 Ma, a difference that is maintained and even appears to increase during cooling from very high temperatures to ca. 350ЊC. Based on the first-order assumption that all the ages are cooling ages, cooling rates in the south are estimated at ca. 7Њ-8ЊC/Ma, while those north of the Lú rio Belt are faster at ca. 16ЊC/Ma. The data are consistent with previous geochronological, petrographic, and field data and suggest a late high-temperature/low-pressure metamorphic event that affected only the basement rocks south of the Lú rio Belt and portions of the latter. This late metamorphism and subsequent delayed, slower cooling agree well with a model of elevated heat flow following lithosphere delamination in the southern part of the orogen, which also explains the observed widespread granitoid magmatism, migmatization, and renewed deformation in the southern basement.

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C–O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis

et al. 2013

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The worldwide 2.33−2.06 Ga unique positive δ13Ccarb excursion has been correlated with the Great Oxidation Event (GOE). The Dashiqiao Formation in the Liaohe Group of the northeastern North China Craton formed at 2.2−2.174 Ga and hosts one of the world‐class magnesite deposits. Here we present major element and C and O isotope analyses of 22 samples from the Dashiqiao Formation and use the data to evaluate the impact of the GOE in the North China Craton, as well as the genesis of the Dashiqiao giant magnesite deposits. Six dolomitic marble samples from a ~600 m thick interval with 1.10 ± 0.04 of MgO/CaO (mol) ratios show higher δ13CPDB values of 0.6−1.4‰ (average 1.2 ± 0.3‰) than those of normal marine carbonates over the globe. However, they display lower δ18OSMOW of 16.4−19.5‰ (average 18.2 ± 1.1‰) as compared to their contemporaneous counterparts, suggesting that the primary carbonates in the Dashiqiao Formation should possess a positive δ13C anomaly (possibly 4.2‰) reflecting the impact of the GOE, and that the δ13C and δ18O values have been depleted in post‐sedimentation diagenesis and/or regional metamorphism. The >550 m thick magnesite layer in the studied section has MgO/CaO ratios ranging from 4.45−200.00. These rocks show δ13C and δ18O values of 0.1−0.9‰ and 9.2−16.9‰, with average values of 0.4 ± 0.2‰ and 13.3 ± 2.5‰, respectively, obviously lower than those of the underlying dolomites. The depletions of 13C and 18O in magnesites relative to dolomitic marbles are interpreted to be the result of hydrothermal alteration related to regional metamorphism leading to rock recrystallization and mass exchange. This interpretation is further confirmed from the hanging‐wall dolomitic marble and the veinlet‐filled magnesite from the ore layer. The former contains mega‐crystals of cylindrical talc and has δ13C of −2.6‰ and δ18O of 14.1‰, indicating that a local fluid–rock interaction between (argillaceous) dolomite and (siliceous) hydrothermal fluids poor in 13C and 18O resulted in the formation of talc and further depletion both in δ13C and in δ18O. The veinlet‐filled magnesite yields δ13C and δ18O values of −2.7‰ and 16.2‰, respectively, showing lower δ13C but higher δ18O than those of massive magnesite in the adjacent strata. Our observation thus strongly supports the interpretation that the massive magnesite interacted with low‐δ13C fluids which were possibly sourced from meteoric water at low temperature during post‐ore time. Thus, the formation of the Dashiqiao magnesite deposits involved primary sedimentation, diagenesis, regional metamorphism, hydrothermal replacement and local post‐ore fluid–rock interaction. Copyright © 2013 John Wiley & Sons, Ltd.

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Depositional environments and an apparent age for the Geci meta-limestones: Constraints on the geological history of northern Mozambique

Cited by 38 publications

References 37 publications

The Geology and Geochemistry of the East African Orogen in Northeastern Mozambique

The Geology and Geochemistry of the East African Orogen in Northeastern Mozambique

Postcollisional High-Grade Metamorphism, Orogenic Collapse, and Differential Cooling of the East African Orogen of Northeast Mozambique

C–O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis

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