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Paper Number: 876

The sources of magmatic rocks matter of the Arctic Ocean and the Central Atlantic Ocean from isotopic geochemical data

Kremenetsky, A.A.¹, Kostitsyn, Yu.A.², Gromalova, N.A.¹, Skolotnev, S.G.³, Shulyatin, O.G.⁴ and Belousova, E.A.⁵

¹IMGRE, 15, ul Veresaeva, Moscow, 121357, Russia; e-mail: nauka@imgre.ru

²GEOKhI, 19, ul. Kosygina, B-334, Moscow, Russia

³GIN, 7 Pyzhevskiy per., Moscow, Russia;

⁴VNIIOkeanologia, 1, Angliiskiy proezd, Saint Petersburg, Russia

⁵ Macquarie University, Faculty of Science, Australia, NSW 2109.

Magmatic rock (basalts, gabbroid, peridotite and plagiogranite) of Central Arctic Rises of the Arctic Ocean (AO) and the crest zone of Mid-Atlantic Ridge (MAR) (Fig. 1) were studied. Samples of basalt from boreholes drilled in the foot of Mendeleev Rise (AO) correspond to volcanic rocks of islands and ocean floor rises by initial isotope ratios of Neodymium (ԑ_Nd(t) +4.3 to +7.0) and Strontium (⁸⁷Sr/⁸⁶Sr 0.70365 to 0.70495). Samples of gabbro-dolerite dredged from the slopes of Mendeleev Rise are grouped in the petrochemical field of low alkalinity, have broad variations of Neodymium isotopic composition (ԑ_Nd –33.1 to +2.9) and Strontium (⁸⁷Sr/⁸⁶Sr 0.7050 to 0.7233) and correspond to the composition of Siberian trapp and other rocks of continental origin (Fig. 2).

Zircons from rocks of AO and MAR are subdivided into two generations: magmatic (0,3-11,5 Ma, MAR and 151-237 Ma, AO) and xenogenic (1250, 1850, and 2500 Ma in AO and MAR) (Fig.3).

Magmatic zircons of MAR have high values of ¹⁷⁶Hf/¹⁷⁷Hf = 0.28310-0.28332 and high positive values of ԑHf (до +21.81), which corresponds to parameters of depleted mantle (Fig. 4). Young magmatic zircons of AO are characterized by decreased values of ¹⁷⁶Hf/¹⁷⁷Hf (0.28214-0.28280) and negative values of ԑHf (up to −19.49), which corresponds to the parameters of continental crust (Fig.4).

In old zircons (1880 and 2500 Ma), initial ratios of Hf isotopes have close values: in AO rocks, ¹⁷⁶Hf/¹⁷⁷Hf = 0.28130 to 0.28195, and in MAR rocks, ¹⁷⁶Hf/¹⁷⁷Hf = 0.28133 to 0.28196. Values of ԑ_Hf(t) are heterogenic and vary in the range from −13.05 to +13.14, plotting symmetrically along chondrite line (Fig. 4), which suggests a single crustal source of matter for all ancient zircons of AO and MAR and supports the incorporation of the major part of xenogenic zircons from ancient Precambrian bedrock.

Figure 1: Sampling chart

Figure 3: U-Pb histograms of zircon dating