SPACE/TIME EVOLUTION OF MAGMATISM IN THE KLAMATH MOUNTAINS PROVINCE (KMP), CA/OR: IMPLICATIONS FOR CORDILLERAN ARC MAGMA PERIODICITY

Magmatic arcs exhibit periodicity at many scales. We present a compilation of over 350 zircon U-Pb crystallization ages from igneous intrusions in the KMP and integrate these data with new calculations of the area and volume of plutons to quantify the space/time magmatic evolution of the KMP. A surge occurred ~400–430 Ma, followed by more widespread magmatism in the Jurassic and Early Cretaceous. Magmatic activity peaked at ~155–175 Ma and ~135–150 Ma. Magmatic flare-ups in the KMP generally last 15–20 myr.

The aerial exposure of the main plutonic suites was measured at regional- and larger-scale in ArcMap. The aerial extent of the plutonic suites are: the neo-Proterozoic – Paleozoic eastern Klamath suite is ~522 km²; the 189–208 Ma Rattlesnake Creek suite is ~57 km²; the 167–174 Ma Western Hayfork suite is ~42 km²; the 168–174 Ma Ironside Mountain suite is ~612 km²; the 155–161 Ma Chetco Complex is ~399 km²; the 154–170 Ma Wooley Creek suite is ~1951 km²; the 143–153 Ma Siskiyou/Western Klamath suite is ~285 km²; the 142–138 Ma TTG suite is ~483 km²; and the 120–145 Ma granodiorite suite is ~614 km². These values are likely minima, especially for the older suites, due to the under-thrusting of successive terranes during Jurassic-Cretaceous orogenesis—a feature that is common to all paleo-magmatic arcs developed in accretionary orogens.

Based on these data we draw the following conclusions: 1) intrusive material was added in discrete batches separated by volumetrically extensive host rock; 2) the locus of plutonism migrated NNE during the Jurassic; 3) the Early Cretaceous magmatism defines a NNW trend along the entire length of the KMP. A preliminary volume estimate for the well-studied/dated 156-159 Ma Wooley Creek batholith is ≥960 km³ indicating a volume addition rate of >320 km³ my^-1. On-going volumetric calculations based on geochemical mass-balances may indicate a substantially greater volume. Volumetric calculations for the entire KMP will be made based on structural cross section restorations, gravity data, geochemical mass balance modeling, and outcrop patterns combined with the exposed relief. Integration of this spatial and temporal data leads to calculations of magma addition rates, which will be normalized to the host terrane area.