POST-SPREADING IGNEOUS ACTIVITY. A GEODYNAMIC MODEL

Abstract

The Nadir volcanic body, which has been mapped in detail, provides an insight into the dynamics of post-spreading activity. This Paleozoic structure is located in the Sartalin ophiolite zone of the Southern Tyan-Shan Range. The geochemical properties of the igneous rocks of the Nadir structure enable us to trace the evolution of the melt, as distinctly manifested by a change in the source from which the basalts were melted out in the course of volcanic activity. Thus, the geological test of post-spreading igneous activity is the presence of fragments of the ophiolite sequence, separated by a tectonic unconformity surface (the zone of ophicalcite breccia) from the overlying pillow lavas, most of which consist of subalkalic basalt derived by partial melting of an undepleted source. This paper makes an attempt to interpret the dynamics of post-spreading igneous activity in terms of the hypothesis of spherical pulsations of the earth, i.e., the postulate that there is a periodic variation in the radius of the earth which is correlated with outbursts of solar activity.