A FIELD-BASED AND REMOTELY SENSED PERSPECTIVE OF MAFIC INTRUSIONS WITHIN MEADOW CREEK BASIN, SOUTHERN BLACK MOUNTAINS, NW AZ

Meadow Creek Basin (MCB) is located in the southern Black Mountains, AZ, near the caldera from which the 18.8 Ma Peach Spring Tuff erupted. In MCB, a series of mafic intrusions cuts through the post-Peach Spring volcanic sequence (Antelope rhyolite, Sitgreaves Tuff [SGT], and Meadow Creek trachyte), providing a glimpse into the movement and storage of mantle-derived material in the time postdating a supereruption. Here, we attempt to establish the spatial and compositional relationships of these mafic intrusions and consider their possible connection to local capping mafic lavas.

We employed both field-based observations and multispectral, remotely sensed data sets. Fieldwork involved collecting samples from each intrusive body, recording contact locations and orientations, followed by in-lab geochemical analyses (XRF) of the samples in order to specify compositional characteristics of the intrusions. Using ArcGIS, we digitized previous geologic mapping by Liggett & Childs (1982), revised to include newly established contacts of four dikes and a newly recognized ~0.5 km by ~1 km lopolith. Remote sensing related methodologies involved performing unsupervised and supervised classifications of the multi-spectral data from field-checked training sites as regions of interest. Using a classification combination, we defined a best-fit map displaying the distribution of the capping mafic lava flow above MCB.

Our results show the intrusions can be divided into three trachyandesite dikes that occur within canyons of the SGT in the west and central parts of the MCB, as well as one diabase dike and an adjacent diabase lopolith (Smith et al, 2016). We estimate that the lopolith has a volume of ~10⁸ m³. The dikes are all nearly vertical and have NW-SE trends that are broadly parallel to many of the normal faults in this region. This suggests a possible syn-extensional relationship between dike emplacement and Miocene crustal lengthening in the SBM. The lopolith and adjacent diabase dike were likely involved with feeding the overlying mafic unit, as confirmed by comparable geochemical signatures (Smith et al, 2016). Similar orientations and dimensions of the dikes, and similar compositions and textures of the mafic dike and lopolith, suggest that all may have been coeval.