AMS IN GRANITES AND LAVA FLOWS: TWO END-MEMBERS OF A CONTINUUM?

Significant differences between granites and lava flows can require different basic assumptions when interpreting AMS results. Among the differences between both types of rocks, perhaps the earliest in being recognized was the wider range of mineral compositions found in granites. Such difference can result in complex mineral assemblages that, in turn, can complicate the interpretation of AMS results in granites relative to the AMS measured in lava flows. Closely linked to this mineralogic effect is the distinction between "primary" flow fabrics and "secondary" effects. Such distinction is a matter of concern in most granites whereas the AMS of lava flows is usually considered "primary" without further examination. However, as the increasing evidence obtained from lava flows shows, the AMS of lavas is not as simple as the general model of hydrodynamic alignment of particles would suggest. As this same general model is commonly employed to interpret the primary fabric of granites, much can be learned from lava flows that can be applied directly to the interpretation of AMS in granites. In this work, the better understanding of the fabric of lava flows that has been obtained in recent years is used as the basis for a reassessment of the basic assumptions needed for the correct interpretation of AMS in both lava flows and granitic rocks.