NORMAN L. BOWEN AND THE ORDER OF CRYSTALLIZATION OF IGNEOUS ROCKS - THE FOUNDATION OF A CAREER

N.L. Bowen’s work, along with the history of igneous petrology in the United States from the late 19^th to the mid-20^th century, has been well-chronicled by Davis Young. There is one early manuscript that stands apart from all the others and as yet has received scant attention. The Order of Crystallization of Igneous Rocks, published in 1912 in the Journal of Geology under the review of J.P. Iddings is a remarkable contribution in many ways. The paper is entirely empirical in its approach such that Bowen first extended the observational analysis of the order of crystallization put forward in Pirsson’s textbook Rocks and Rock Minerals into the three-dimensionality of igneous textures. Bowen concluded that the only compelling evidence provided is the order of cessation of crystallization rather than the commonly held understanding of the order of initiation of crystallization as derived from Rosenbusch’s Law.

Building on experiences from the Geophysical Laboratory, Bowen posits an analogy between quenching of experiments in igneous geochemistry and checking of crystallization of magmas during eruption such that the mineralogy and textures of rhyolites could be used to provide evidence for the order of initiation of crystallization of granite. By evaluating the effusive equivalents of syenite, quartz diorite, diorite, and gabbro Bowen was able to propose an order of initiation of crystallization for those plutonic rocks. Through this Bowen was building an empirical foundation for the theoretical work that would consume the remainder of his career. A primary characteristic of Bowen’s science was in addition to proposing and testing his own hypotheses to directly challenge those of other workers and this first takes shape in this paper.

In the subsequent volume of the Journal of Geology Victor Ziegler questioned Bowen’s assumptions regarding use of effusive rocks as analogs of the order of crystallization of their plutonic equivalents and concluded the overlapping of both the beginning and cessation of crystallization of one mineral by another was improbable. In his pointed response to Ziegler, Bowen took the opportunity to more clearly and forcefully link the petrographic evidence presented to the concepts of differentiation of rock magmas and highlight the absence of evidence of eutectic, that is simultaneous, cessation of crystallization in multi-component igneous systems.