FIELDWORK REMAINS INDISPENSABLE TO GEOLOGICAL STUDIES WHILE OFFERING OPPORTUNITIES FOR SYNERGY WITH ANALYTICAL METHODS: EXAMPLES FROM COSTA RICA AND TAIWAN

Recently completed field investigations in Costa Rica and Taiwan emphasize the essential role that fieldwork plays in modern geological research in spite of the rapidly growing use of analytical methods. Here we share outcomes that showcase (1) how indispensable fieldwork is, and (2) the synergy that is possible by combining fieldwork with remotely derived data and/or analytical tools. Aerial photography and Shuttle Radar Topography Mission (SRTM) derived Digital Elevation Models (DEMs) reveal targets for field studies (i.e., lineaments) in the upper plate at the Cocos Ridge collision in Costa Rica. The ridge is colliding at a high angle to the Middle America Trench at ~81 mm/yr, and active upper plate strike-slip faults have been described. However, owing to tropical weathering most outcrops are ephemeral, consisting of saprolite of parent volcanic units. During the last decade, one of us (JCL) has visited many such outcrops with collaborators – several examples highlight how critical field observations are. Aerial photography, DEMs and LiDAR data in Taiwan likewise reveal targets for fieldwork. Relative to the passive margin of China, the Luzon volcanic arc is colliding obliquely at ~82 mm/yr. Although the subtropical weathering of Taiwan is quite vigorous, the bedrock exhumation rates are sufficient that fresh metamorphic basement exposures can be found. The challenge to fieldwork is that the high exhumation rates combined with the strong rock fabrics, yield landscapes with abundant stream knickpoints, unstable slopes and impassible streams. In recent years both of us have managed to collect data and samples from highway and river exposures that have proven indispensable. Importantly, newly developed methods by one of us (YCC), of 3D mapping using GIS tools has demonstrated that is possible to generate bedrock maps that are far more accurate than those based on field mapping. Rather than obviating field mapping, these findings make it clear that fieldwork is essential for evaluating the digitally derived maps and for making field observations of details that are not possible with remote sensing data (e.g., measuring fault kinematic data and/or non-penetrative foliations). We imagine an evolving paradigm where digital mapping takes place first, followed by detailed and targeted fieldwork.