INTERACTIVE DATA LANGUAGE MAPPING FOR QUANTITATIVE PETROGRAPHIC CHARACTERIZATION: PALISADES FERRO-BASALTS AND GRANOPHYRES

Bulk chemistry, trace chemistry and microprobe data sets have traditionally been used to establish a framework for mapping facies along cross-sections of complex basalt sills and dikes, such as the Palisades Sill of New York and New Jersey. Image-analysis of thin sections is presently proposed as an inexpensive and rapid supplemental tool for identifying and tracing mineralogically-defined horizons. Tested parameters include relative mineral content, mineral color, mineral morphology and related features. An image analysis method is based on Interactive Data Language (IDL) software interpretations of petrographic images acquired using a Spot-RT CCD camera and a Zeiss research petrographic microscope. IDL routines are used to define petrographically important characteristics, such as ophitic texture, crystal elongation, quartz content and related features. Compilations of data are applied to evaluating petrographic differences between various texturally distinct melanocratic facies of the George Washington Bridge and Upper Nyack sections of the Palisades Sill of New York and New Jersey. These correlations illustrate the value of the image-analysis methods in the field of quantitative petrography.