AN INVESTIGATION OF THE GRANITES AND RHYOLITES OF THE WICHITA MOUNTAINS IGNEOUS PROVINCE, SOUTHWESTERN OKLAHOMA USING SEM-CL: TEXTURAL FEATURES OF QUARTZ CRYSTALS REFLECT CRYSTALLIZATION HISTORIES

When examined with scanned cathodoluminescence (SEM-CL), volcanic and plutonic quartz crystals display distinct characteristic textures not evident using other petrographic techniques. Examination of a suite of igneous rocks from the Wichita Mountains indicates that SEM-CL has the potential to be an effective method of revealing magma conditions during ascent and emplacement and, used in conjunction with other analytical techniques, provides the opportunity to better understand the nature and evolution of magmatic processes.

Plutonic quartz textures include: filled fractures and non-luminescent dark patches and CL streaks. Volcanic quartz displays distinct concentric oscillatory zoning. SEM-CL textures are interpreted to result from a range of sources including lattice defects, trace element impurities, fluid inclusions, stress fractures, and disruption of growth and diffusion rates during crystallization.

Quartz from the Carlton Rhyolite and Wichita Granites Wichita Mountains igneous province, southern Oklahoma) was studied in an attempt to relate textural features of quartz crystals to magmatic crystallization histories. Research indicates that initial eruption of large amounts of rhyolite above an older gabbroic complex created a crustal magma trap, allowing subsequent magma batches to pond and crystallize at depth, resulting in early fine-grained granites and later coarser-grained granites. SEM-CL textures of the three common igneous rock types (rhyolite, early and late granites) reflect their respective crystallization histories. Carlton Rhyolite quartz is commonly euhedral and displays oscillatory zoning, reflecting primary crystal growth in a compositionally variable melt prior to eruption. Quartz from fine-grained Mount Scott Granite displays embayed margins with margin-parallel zoning, possibly due to depressurization during ascent with continued crystallization upon emplacement. Quartz from coarse-grained Quanah Granite exhibits limited zoning and embayed margins, indicating higher H₂O content and emplacement at deeper crustal levels, both due to increased overburden.

SEM-CL provides previously unrecognized information of internal structures and features of quartz, and promises to be an essential tool in interpreting the evolution of magmatic processes.