Paper No. 33-9
Presentation Time: 10:55 AM
POTENTIAL SIGNIFICANCE AND IMPLICATIONS OF THE LATE CRETACEOUS TEUTONIA BATHOLITH (MOJAVE NATIONAL PRESERVE, CA) FOR LARAMIDE TECTONISM
The Teutonia batholith is a large intrusive suite with loosely constrained Late Cretaceous emplacement ages (zircon U-Pb ages of ~88 Ma and ~82 Ma; Barth et al., 2004) located within the Mojave National Preserve of eastern California. Emplacement of the Teutonia batholith coincides with onset of the most voluminous phase of Mojave region, which progresses southwest into Joshua Tree National Park until ~72 Ma, allow for study of upper crustal tectono-magmatic processes during the transition from Sevier to Laramide deformation. Testable hypotheses that may elucidate the significance of the Teutonia batholith include: 1) Does the Teutonia Batholith represent a tectonically, chronologically and geochemically distinct event separate from broader Late Cretaceous Mojave granitic magmatism? Or, 2) Does the Teutonia Batholith represent an early pulse of continuous magmatism that results in the voluminous Mojave region plutons? Either result has implications for Laramide tectonism: If Hypothesis 1 is correct, the state of the crust and mantle during Teutonia plutonism will provide constraints on the tectonic environment of the widespread Cretaceous Mojave plutonism. If Hypothesis 2 is correct, it represents a stumbling block for current models of flat-slab driven tectonism due to the lack of a magmatic gap during slab passage.
New geochemical and petrographic data highlight compositional diversity of Teutonia plutons noted by Beckerman et al. (1982). Lithologies range from clinopyroxene-hornblende gabbro to granites. The volume of mafic and mafic-intermediate plutons is a distinctive feature of the batholith, including ~8km2 continuous exposure of the Black Canyon gabbro. Gabbros display compositional and textural heterogeneity including pods of layered coarse-grained hornblende megacrysts and layered quartz diorites; cumulate textures coincide with lower Mg#s, however, zones of gabbros with more magmatic textures have Mg#s as high at 67. Gabbros and diorites define an iron-enrichment trend with tholeiitic affinity, whereas felsic and more evolved compositions are calc-alkaline and follow trends defined by the Late Cretaceous Cadiz Valley batholith. Teutonia whole rock trace element data yield negative Nb and Ta anomalies, and mirror Sr/Y ratios of the Cadiz Valley batholith and Joshua Tree plutons.