Scientific publications

In the Cenozoic basalts of Iceland, along with syngenetic crystals, older xenogenic zircon grains were discovered, forming an age range from the Pleistocene to the Mesoarchean, and about 70 % of the ages are concordant. Zircon syngenetic crystals account for 2 % of the total number of grains, and the percentage distribution of xenogenic grains is as follows: Mesozoic – 7, Paleozoic – 24, Neoproterozoic – 16, Mesoproterozoic – 24, Paleoproterozoic – 23, Neoarchean – 3, and Mesoarchean – 1. About 90 % of the studied grains have a Th/U ratio  0.3, characteristic of magmatic zircons. About 3 % of crystals fall in the field of metamorphic zircon compositions (Th/U  0.1), and 10 % of grains are metamorphosed zircons of magmatic genesis (Th/U = 0.1–0.3). Based on the ages and results of Lu-Hf isotopic systematics, xenogenic zircon crystals were clustered into five groups with intervals of 100–200, 300–500, 900–1200, 1700–1900, 2000–2650 Ma, formed, respectively, by zircons of the rocks of the Central Atlantic Magmatic Province (CAMP), the Caledonian orogeny, Grenville-Sveconorwegian orogen, Svecofennian granites, and derivatives of the ancient sialic crust – TTG complexes and eclogites. In their REE concentrations and distribution patterns, the Phanerozoic and Precambrian xenogenic zircons are similar, respectively, to zircons from basalts and gabbro of the Arctic Ocean (AO) and the Mid-Atlantic ridge (MAR), with ages of 97–153 and 1500–1900 Ma. Based on the concentrations of highly charged elements – Y, U, Yb, Hf, the composition points of the Phanerozoic and Precambrian xenogenic zircons are located within the field of continental derivatives. The presence of ancient zircons in the Cenozoic basalts of Iceland is probably due to the contamination of basaltic melts with matter from sections of the continental crust located in the spreading zone, with the zircons retaining information about the age and stages of lithospheric transformation in the interval of about 3 billion years.