HR: 0800h
AN: V41C-1455    [Abstracts]
TI: Testing Magmatic Emplacement Mechanisms in the Balcones Igneous Province of Texas
AU: * Griffin, W R
EM: griffin@utdallas.edu
AF: University of Texas at Dallas, Geosciences, PO Box 830688, FO21, Richardson, TX 75083
AU: Bergman, S C
EM: bergman@utdallas.edu
AF: University of Texas at Dallas, Geosciences, PO Box 830688, FO21, Richardson, TX 75083
AU: Leybourne, M I
EM: mleybo@utdallas.edu
AF: University of Texas at Dallas, Geosciences, PO Box 830688, FO21, Richardson, TX 75083
AB: Various intraplate volcanic fields, large igneous provinces, and continental flood basalt provinces have long been considered to be the result of mantle plumes interacting with the lithosphere, an idea supported by the recognition that the geochemical and isotopic compositions of intraplate magmatism differ significantly from those of mid-ocean ridge and arc settings. However, not all intraplate magmatism fits the mantle plume model. Ad-hoc refinements to the original models of Wilson and Morgan to explain anomalous characteristics has prompted a global debate within the geoscience community ranging from the number of mantle plumes that exist, to the very existence of mantle plumes. An outgrowth of this ongoing debate has been the proposal of a number of alternative models that attempt to explain the existence of intraplate magmatism in the absence of a mantle plume source. The Balcones Igneous Province (BIP) of south central Texas provides an excellent opportunity to investigate magmatic processes that occur in a continental intraplate setting. An integrated field, geochemical, and geochronologic study is in progress in the BIP to understand the petrogenetic processes and magmatic emplacement mechanisms responsible for its formation. The BIP is an arcuate zone of Late Cretaceous (86-77 Ma) intraplate volcanic and intrusive igneous bodies approximately 400 km in length by 100 km in width. Initial geochemical analyses (n=12; major element, trace element, rare-earth element, radiogenic isotope (Sr, Nd, Pb) and mineral composition) from the BIP suggest magmatism resulted from small degrees of partial melting in the garnet stability zone of a depleted mantle source that had experienced re-enrichment in incompatible trace elements. Although previous workers have suggested BIP magmatism may be related to OIB type sources, it is likely that several upper mantle magmatic processes were involved. Initial geochronological analyses (n=7; U/Pb SHRIMP, 40Ar/39Ar) from the BIP demonstrate magmatism occurred over a much shorter time-period than previously thought. Regional geophysical data indicate the BIP coincides with the inner margin separating Neoproterozoic (1.3 Ga) cratonic lithosphere, from much younger (Paleozoic to Mesozoic) transitional lithosphere of the southern margin of the North American continent. Uncertainties exist regarding the lithospheric transition zones to the west into Mexico and Trans-Pecos (TP) Texas, because Mesozoic and Cenozoic tectonic events have effectively masked much of the earlier evidence in the region. Our work has produced new geochronological evidence from TP Texas that demonstrates mafic magmatism was present in the region at 73 Ma (U/Pb SHRIMP), similar in age to that of the BIP, suggesting the BIP may extend 400 km further west that previously recognized. Alkaline silica undersaturated igneous complexes in northern Coahuila, Mexico appear to provide a spatial link between the south Texas and TP Texas segments. In a broader regional context, the BIP may represent a small segment of a Middle to Late Cretaceous Gulf Coast diffuse igneous province, as large as 1400 x 200 km, comprising igneous centers in central Arkansas, northeast Louisiana and central Mississippi. Similar geochemical compositions and emplacement ages across the region support this idea.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005