Evolution of granitoids in the Catalina metamorphic core complex, southeastern Arizona: U–Pb, Nd, and Hf isotopic constraints

Abstract

The Santa Catalina Mountains, SE Arizona, was one of the first metamorphic core complexes to be described. Despite its status as a type example, relatively little is known about precise ages and origins of the intrusive rocks that make up most of the crystalline core. U–Pb and Hf isotopic data by laser ablation–inductively coupled plasma–mass spectrometry from zircons and Nd isotopic results from whole rocks were obtained for 12 granitoids ranging from 1,440 to 26 Ma. Results confirm that the 1.44-Ga Oracle Granite extends through the Catalina Range as variably mylonitic granite and banded gneiss. Laramide intrusions (67–73 Ma) display initial eNd values −5 to −8 and eHf from −7.5 to −9. Magmatic ages for the prominent white granite sills of the Wilderness suite are 46–57 Ma, in agreement with Terrien (2012), and these granites have initial eNd values −8 to −10 and eHf from −7 to −14. Lastly, the undeformed Catalina Granite has an age of 26 Ma, with an initial eNd and eHf of −6 and −8, respectively. Our Nd results agree with limited results from Farmer and DePaolo (89:10141–10160, 1984). Although the Catalina Granite seems to have a significant juvenile component based on Nd and Hf, most of the Laramide and Wilderness intrusions contain Nd and Hf compositions lying close to the evolution of 1.44-Ga Oracle Granites, a fact that is confirmed by the U–Pb data, which show both 1.7- and 1.4-Ga zircon cores in these samples, with 1.4 Ga as the dominant core age. In order to become the dominant source of most of the 72–45-Ma magmas, the Oracle pluton must not only extend across the whole Catalina region, but also have abundant deep-seated equivalents to provide magma sources.