Petrology and geochemistry of Mesozoic dolerites from the Hinlopenstretet area, Svalbard

Abstract

Middle Jurassic to Lower Cretaceous dolerite intrusions have a widespread occurrence throughout the Svalbard archipelago, especially in the Hinlopenstretet area. Petrographic and geochemical studies of ten samples collected near intrusion contacts from the Lomfjorden Sill and Wilhelmeya Island confirm that these dolerites are tholeiitic. Augite in these rocks is colorless to a distinct purplish-brown, which is unusual for this mineral in tholeiitic rocks. In spite of the high TiO₂ contents (0.8—2.9 wt. %), which classify it as titania-rich augite to titanaugite, this augite is compositionally more similar to augite from other tholeiitic intrusions than to titanaugite from alkalic basalts. The samples are compositionally uniform (SiOa — 49.7—50.4 wt. %, MgO = 5.1—5.8 wt. %) and are characterized by high contents of TiO₂ (3.3—3.6 wt. %) and opaque minerals (6—11 vol. %). The age and tholeiitic nature of these intrusions are consistent with the interpretation that they were associated with the extensional tectonics related to the generation of the Amerasia Basin.