Tectonomagmatic evolution of southwestern Laurentia: Insights from zircon U-Pb geochronology and hafnium isotopic composition of the Red Bluff Granite Suite, west Texas, USA

Abstract

We provide laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) and high-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb ages and Hf isotopic compositions of zircons from the Red Bluff Granite Suite and mafic dikes in the Franklin Mountains of El Paso, Texas, USA. Granitoids exposed in the Franklin Mountains were previously divided into five magmatic stages based on cross-cutting relationships. Major and trace element compositions showed that these granitoids are ferroan, alkaline, and A2 type. Homogeneity in the whole-rock geochemistry suggests that the granite stages are genetically related and share similar petrogenetic histories. Weighted mean zircon 206Pb/238U dates from the older magmatic stage 1 alkali-feldspar quartz syenite and stage 2 alkali-feldspar granite are 1112.36 ± 0.35 and 1112.46 ± 0.37 Ma, respectively. The weighted mean εHf(t) values varying from +5.3 to +7.2 are similar to those of other regional ca. 1.1 Ga magmatic rocks throughout south- western Laurentia. Geochemical characteristics, petrological modeling, and enriched Hf isotopic composition suggest fractional crystallization of a basaltic magma that was produced by melting of an enriched mantle reservoir. However, zircon inheritance ages of ca. 1.3 Ga and 1.26–1.15 Ga are consistent with a minor contribution from felsic crustal basement. Our data and regional geology are consistent with a post-collisional slab break-off that facilitated asthenospheric upwelling and partial melting of the enriched mantle, possibly subcontinental lithospheric mantle, extending from Llano Uplift, Texas, in the southeast to California to the northwest. Magma thus generated upon differentiation produced ferroan and A-type granitoids.

Crustal Architecture of the Paleo‐Pacific Rift Margin of East Antarctica: Evidence From U‐Pb Ages and O‐Hf Isotope Compositions of Ross Orogen Granitoids

“…1.1-1.2 Ga rocks and erratics from Antarctica correspond with ages of igneous units from the Grenville province of southwest Laurentia that extend across Texas, Sonora, and eastern California, and that occur in Colorado at Pikes Peak (Howard, 2013;Mahar et al, 2023;Rämö et al, 2003;Wooden et al, 2013). These Grenville Province rocks range in age from 1065 to 1220 Ma and have ε Hf(i) values from about 1 to +7 (Howard, 2013;Mahar et al, 2023;Wooden et al, 2013; and recalculated from Nd isotope data of Rämö et al, 2003), overlapping with Antarctic samples of the same age (Figure 21). Together, these coeval igneous ages indicate that the Grenville Orogen may extend into the TAM margin of East Antarctica, but as noted previously ice cover and younger tectonic events obscure whether, or where, such Grenvillian-type basement may exist (see Loewy et al, 2011).…”

“…The ca. 1.1-1.2 Ga rocks and erratics from Antarctica correspond with ages of igneous units from the Grenville province of southwest Laurentia that extend across Texas, Sonora, and eastern California, and that occur in Colorado at Pikes Peak (Howard, 2013;Mahar et al, 2023;Rämö et al, 2003;Wooden et al, 2013). These Grenville Province rocks range in age from 1065 to 1220 Ma and have ε Hf(i) values from about 1 to +7 (Howard, 2013;Mahar et al, 2023;Wooden et al, 2013; and recalculated from Nd isotope data of Rämö et al, 2003), overlapping with Antarctic samples of the same age (Figure 21).…”

“…(2013), and Mahar et al. (2023); Laurentian A‐type granitoids from Mojave and Yavapai crustal provinces, Goodge and Vervoort (2006) and Wooden et al. (2013); Mojave province igneous basement, Wooden et al.…”

“…In Antarctica, these include high-grade gneisses and schists of the Nimrod Complex, formed during igneous and metamorphic events at ca. 1.7, 2.5, 2.9, and 3.1 Ga (see Goodge & Fanning, 2016), and by basement igneous units from the Goodge et al (2008Goodge et al ( , 2017; Shackleton Range igneous basement, Will et al (2010); igneous basement from Australian Gawler craton, Reid and Payne (2017); southwest US Grenvillian igneous rocks, Howard (2013), Rämö et al (2003, recalculated from Nd isotope data), Wooden et al (2013), andMahar et al (2023); Laurentian A-type granitoids from Mojave and Yavapai crustal provinces, Goodge and Vervoort (2006) and Wooden et al (2013); Mojave province igneous basement, Wooden et al (2013); and Clearwater Block igneous basement, Wang et al (2022). Nimrod Complex igneous events are shown by vertical pink bands (see Goodge & Fanning, 2016).…”