U–Pb–Hf isotope systematics of detrital zircons in high-grade paragneisses of the Ancient Gneiss Complex, Swaziland: Evidence for two periods of juvenile crust formation, Paleo- and Mesoarchaean sediment deposition, and 3.23 Ga terrane accretion

Komatiitic magmatism is a characteristic feature of Archean cratons, diagnostic of the addition of juvenile crust, and a clue to the thermal evolution of early Earth lithosphere. The Slave craton in northwest Canada contains >20 greenstone belts but no identified komatiite. The reason for this dearth of komatiite, when compared to other Archean cratons, remains enigmatic. The Central Slave Cover Group (ca. 2.85 Ga) includes fuchsitic quartzite with relict detrital chromite grains in heavy-mineral laminations. Major and platinum group element systematics indicate that the chromites were derived from Al-undepleted komatiitic dunites. The chromites have low 187Os/188Os ratios relative to chondrite with a narrow range of rhenium depletion ages at 3.19 ± 0.12 Ga. While these ages overlap a documented crust formation event, they identify an unrecognized addition of juvenile crust that is not preserved in the bedrock exposures or the zircon isotopic data. The documentation of komatiitic magmatism via detrital chromites indicates a region of thin lithospheric mantle at ca. 3.2 Ga, either within or at the edge of the protocratonic nucleus. This study demonstrates the applicability of detrital chromites in provenance studies, augmenting the record supplied by detrital zircons.

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U-Pb age and Lu-Hf isotope systematics of detrital zircons from paragneiss of the Bulun block (Sharyzhalgai uplift of the Siberian Craton Basement)

Doklady Earth Sciences ◽

10.1134/s1028334x14100225 ◽

2014 ◽

Vol 458 (2) ◽

pp. 1265-1272 ◽

Cited By ~ 6

Author(s):

O. M. Turkina ◽

E. N. Lepekhina ◽

N. G. Berezhnaya ◽

I. N. Kapitonov

Keyword(s):

Siberian Craton ◽

Detrital Zircons ◽

Hf Isotope ◽

Isotope Systematics

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Age, HF-isotope systemantics of detritial zircons and the source of conglomerates of the mt. Southern Demerdzhy, Mountainous Crimea

Геотектоника ◽

10.31857/s0016-853x2019536-61 ◽

2019 ◽

pp. 36-61

Author(s):

S. V. Rud’ko ◽

N. B. Kuznetsov ◽

E. A. Belousova ◽

T. V. Romanyuk

Keyword(s):

Middle Jurassic ◽

Age Distribution ◽

Primary Source ◽

Upper Jurassic ◽

Detrital Zircons ◽

Hf Isotope ◽

Coarse Grained ◽

East European ◽

Scythian Plate ◽

Isotope Systematics

The U–Pb dating and Hf isotope systematics of detrital zircons from a sandstone interbed in the section of the upper conglomerate sequence of the Mt. South Demerdzhi were carried out. The dominant populations of detrital zircons in the studied sample characterize episodes of magmatic activity within the source of the Upper Jurassic conglomerates. Magmatism was manifested in the Vendian-Cambrian, Carbon-Triassic and Late Jurassic. The åHf values of detrital zircons of these ages indicate the insignificant role of the ancient (Archean–Early Proterozoic) continental crust in the protolith of magmatic chambers. The similarity of the detrital zircons age distribution from the Middle Jurassic and Upper Jurassic conglomerate strata suggests that they are molasses of the Cimmerian orogen. The absence of products of Middle Jurassic magmatism in molasses of the Cimmerian orogen, which we fixed, limits position of the Cimmerian orogen in the southern part of the Scythian plate. It is shown that the primary source of the Precambrian detrital zircons were mobilized within the Cimmerian orogen the crustal fragments of the Peri-Gondwanan origin, rather than the basement complexes of the East European Platform, similar to the complexes of the Ukrainian shield. The reconstruction of the main stages of the accumulation of the coarse-grained strata of the Mountaineous Crimea in the context of the tectonic evolution of the southern margin of Laurasia during the Mesozoic is presented.

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