Trace element and isotopic geochemistry of Cretaceous magmatism in NE Asia: Spatial zonation, temporal evolution, and tectonic controls

Abstract

Results of a comprehensive geochemical study (major and trace elements, and isotopes of Sr, Nd, Pb, Hf) of Cretaceous volcanic rocks from the Chukotka area in northeastern Russia are presented. Synthesis of available geological and geochronological data suggests diachronous onset of activity of the Okhotsk–Chukotka volcanic belt (OCVB), the largest magmatic province in the region. The OCVB consists of ca. 106km3 of volcanic rocks. At 106–105Ma, subduction-related magmatism initiated in the southern and central segments of the OCVB. In the Central and Northern Chukotka areas, where the northern OCVB is exposed, onset of arc magmatism occurred ca. 10m.y. after extension-related magmatism of the Chaun igneous province at 109–104Ma. Mafic rocks from the OCVB yield (87Sr/86Sr)80Ma of 0.7033 to 0.7047, εNd80Ma of 0.0 to 7.10, εHf80Ma of 4.12 to 12.88, (206Pb/204Pb)80Ma of 18.11 to 18.42, and (208Pb/204Pb)80Ma of 37.96 to 38.21. Volcanic rocks from the Chaun province, as well as OCVB rocks from Northern Chukotka, originate from a relatively enriched source and have (87Sr/86Sr)80Ma of 0.7088 to 0.7100, εNd80Ma of −5.81 to −3.42, εHf80Ma of −3.40 to −0.25, (206Pb/204Pb)80Ma of 18.69 to 18.90, and (208Pb/204Pb)80Ma of 38.65 to 38.86. No definitive across-arc elemental or isotopic zonation of the OCVB has been revealed, probably because of wide-scale crustal melting and subsequent contamination of mantle-derived melts. However, there is a clear along-arc isotopic zonation. In our interpretation, this results from heterogeneity of the subcontinental lithospheric mantle, which likely was a major contributor to the magma source. The similar isotopic signatures of silicic (dominantly crust-derived) and mafic (mantle-derived) volcanic rocks in each OCVB segment imply that remelting of juvenile mafic underplated material was the main process responsible for the crust-derived magma generation. These data from the major Cretaceous magmatic provinces of northeast Asia are synthesized in context of existing plate tectonic reconstructions.