SAGE HEN FLAT, WHITE MOUNTAINS, CALIFORNIA: AN EXPLORATION IN PLUTON EMPLACEMENT, CERTAINTY IN DATA, AND THE UTILITY OF SALIENCE MAPS

The Jurassic Sage Hen Flat pluton, California, is colloquially referred to as a “cookie cutter” pluton, because the wallrock patterns are not disrupted by the emplacement. We investigate the emplacement and subsequent deformation of this pluton using traditional field methods in addition to the techniques developed in collaboration between cognitive scientists and geologists, work facilitated by A. Sylvester. First, we present data on field fabric, thin section, magnetic, and a gravity survey to support the emplacement of the Sage Hen pluton as a thin sheet. Then, we introduce the concepts of uncertainty measurements and salience maps while demonstrating their utility as tools for geologic practitioners.

The Sage Hen flat pluton and surrounding rocks are affected by Miocene-present normal faults. These faults are best observed away from the plutons, where they affect the shallowly dipping basalt flows. However, these faults strike toward the Sage Hen flat pluton. While offsets are locally visible at contacts, they are quite difficult to recognize in the center of the pluton. Thus, most of our inferences about the presence of faults would not be recorded in a scientific manuscript or on a geological map. Basically, the presence or absence of faults are smaller models that impact the larger model of pluton emplacement. In other words, the overarching model (pluton emplacement) is only as certain, and is a product of smaller scale models (e.g., faults), which are – in turn - only as certain as the individual’s recorded observations (e.g., this contact is offset).

We propose the use of “salience maps” to communicate results and mental classifications associated with geological studies that are often neglected (e.g., cryptic faults). Salience maps explicitly communicate the importance, predictability, and relevance of a given map region. These maps also provide explicit links between data and models, as well as being communication tools between current and future practitioners. Creating salience maps while in the field can help current practitioners to remember field relations more clearly and provide information about the importance of a given outcrop/data point. The use of salience maps will allow geologists to work together more efficiently and effectively as a community to solve geological problem.