Three-dimensional computer modeling of fabric evolution in igneous rocks

The fabric of an igneous rock is defined by the sizes, shapes and orientations of its crystals; the spatial distributions and concentrations of elements within the crystals; and the nature of the grain boundaries. FABRIC is the name of a collection of programs consisting of five main program files, four subroutine files, and a control block file for the graphical modeling of fabric development in three dimensions in the crystallization of magma. Crystals grow by the joining of nodes around the margins of crystals in a layered fashion. The nodal pattern for each type of crystal is unique, similar to the spacing of unit cells, and is defined by the user in the control block file. The model generates a database of the (x, y, z) coordinates and other attributes of each joined node in ascending order. The database can be sorted for records with special attributes with a database manager. The plotting of nodes in an (x,y) slice through the crystallized volume renders an animation of the joining of nodes to growing euhedral crystals in that slice. FABRIC is designed in a modular fashion for general use, but the present version deals with the simultaneous growth of euhedral crystals to their contiguity upon which growth collision boundaries rather than crystal faces develop. The angles that the growth collision boundaries make with the colliding faces may be used to determine the ratio of the velocities of advance of the faces in special cases. The final fabric resembles the allotriomorphic fabric found in some igneous rocks. (C) 2001 Elsevier Science Ltd. All rights reserved.