Chemical and isotopic compositions of rocks and minerals from the Franz Josef Land Archipelago

Rb, Sr, Sm, Nd, U, and Pb contents and Sr, Nd, and Pb isotopic composition were determined in tholeiite and subalkaline basalts (in both whole-rock samples and individual minerals) from the Franz Josef Land Archipelago. Isotopic data obtained for the Arctic basin are similar to those for islands from the Pacific, Atlantic, and Indian oceans. The assimilation of crustal (sedimentary) rocks by primary depleted material makes isochron determination of basalt age difficult or impossible. The subalkaline basalts (basaltic andesites) were presumably formed by the metasomatic introduction of incompatible elements in tholeiitie basalts and, only partially, through crustal contamination and fractional crystallization.

Chemical composition, age, and magnetic parameters of igneous rocks from the Franz Josef Land

A combined study of magnetic parameters of basalt and andesite samples has been carried out in the framework of geological investigations of the Franz Josef Land. This study has included determination of coercivity, saturation magnetization, Curie points, natural remanent magnetization (NRM), and magnetic susceptibility as well as examination of ferromagnetic minerals with a microscope. Data on chemical composition of the rocks have been obtained for all the samples, and radiological ages have been determined for the majority of the rocks. Thermomagnetic curves of the samples have been subdivided into four types depending on composition of ferromagnetic NRM carriers. Data showing multiple changes in the predominant composition of the igneous rocks have been obtained. Each stage of magmatism is characterized by a specific type of the ferromagnetic component in the rocks and, therefore, magnetomineralogical investigations can be used for differentiation and correlation of the igneous rocks.