10 - The paragenesis of serendibite at Johnsburg, New York, USA: an example of boron enrichment in the granulite facies

Summary

Introduction

In his studies of metasomatic deposits beginning in 1936, D.S Korzhinskiy proposed the concept of thermodynamic systems with ‘perfectly mobile’ components and the application of the phase rule to such systems. Much of Korzhinskiy's work concerned the theory of open systems, ‘perfectly mobile’ components, and rigorous application of the Gibbs method to understanding metasomatic deposits.

The principles developed by Korzhinskiy are ideally suited to study the paragenesis of serendibite, a Ca–Mg–Al borosilicate closely related to aenigmatite and sapphirine in crystal structure (Machin & Süsse, 1974). At all the known world localities (Table 10.1), including Johnsburg, New York, the subject of the present paper, serendibite formation was associated with metasomatism at high temperature over a range of pressures in the granulite facies, upper amphibolite facies (Melville Peninsula), or in contact aureoles (Riverside, California). For petrologists, the major questions concerning serendibite are the origin of the boron and the mechanism for its enrichment in the serendibite-bearing rocks. Boron-enriched rocks are rare in granulite-facies terrains, which are generally depleted in boron relative to amphibolite-facies terrains (e.g. Truscott et al., 1986). Thus the Johnsburg locality offers a unique opportunity to consider the question of boron enrichment under granulite-facies conditions.

The present study is based on field observations and samples obtained by G.H. Swihart and P.B. Moore in 1983 and 1984, and by E.S. Grew in 1985 and 1986.