Mostly consisting of tholeiite basalt with minor amounts of hyaloclastite and rhyolite, the total thickness of the strata from this volcano is estimated to be 2, 700 m.
12.
The groundmass contains interstitial quartz or tridymite or cristobalite . " Olivine tholeiite " has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass.
13.
Boninites can be derived from the peridotite residue of earlier arc tholeiite generation which is metasomatically enriched in LREE before boninite volcanism, or arc tholeiites and boninites can be derived from a variably depleted peridotite source which has been variably metasomatised in LREE.
14.
Isotope ratios of He / 4 He, are also of great value : for instance, ratios for basalts range from 6 to 10 for mid-ocean ridge tholeiite ( normalized to atmospheric values ), but to 15 24 and more for ocean-island basalts thought to be derived from mantle plumes.
15.
Within the Murmansk block, from west to east, there is an increase in the rare earth elements ( REE ) content in the initial melts, a change in composition of protoliths from tholeiite with the highest content of REE to subalkaline basalt, and in the eastern part of the Murmansk block the REE content is even higher.
