Geodynamic formation conditions of Early Cambrian lavas in the Ozernaya zone of Mongolia

Four types of pre-accretionary Early Cambrian lava sequences are distinguishable in the geological structure of the Ozernaya zone in western Mongolia: (I) close to N-MORB; (II) close to E-MORB; (III) enriched with trace elements and with HFSE minimums; (IV) depleted in trace elements and with HFSE minimums. All these lavas could have been formed in an island-arc‒back-arc basin system. N-MORB basalts were melted from depleted magma sources with с ε Nd ( t ) = 10.0–11.5. Plume melts originated from mantle sources with ε Nd ( t ) = 4.8–9.7. The sources of island arc lavas were characterized by ε Nd ( t ) = 7.3–9.9.