GSA Connects 2021 in Portland, Oregon

Paper No. 157-6
Presentation Time: 9:00 AM-1:00 PM


ARDILL, Katie, Geology Department, California State University, Sacramento, 6000 J St, Sacramento, CA 95819, ATTIA, Snir, New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, 801, Socorro, NM 87801, PATERSON, Scott, Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, MEMETI, Vali, Department of Geological Sciences, California State University Fullerton, 800 N State College Blvd, Fullerton, CA 92831 and BORSOOK, Ariel, Department of Earth Sciences, University of Southern California, Zumberge Hall of Science (ZHS), 3651 Trousdale Pkwy, Los Angeles, CA 90089; Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401

Geochemical signals of arc products broadly characterize source materials and subsequent magma processes operating during magma ascent from the mantle to the surface. However, the dynamic and episodic nature of long-lived continental arc systems modifies these signals as the arc is not static, but spatially and temporally evolving.

To deconstruct spatial and temporal geochemical patterns, we compiled age-constrained geochemical bulk rock data (n= 1816 samples) across Mesozoic plutonic, hypabyssal, and volcanic rocks in the central Sierra Nevada (CSN), eastern CA, of which ~6150km2 (52% of area, [1]) was emplaced during Cretaceous eastward arc migration, flare-up, focusing, and crustal thickening. Cretaceous signals were compared to Jurassic and Triassic flare-up signals that currently lack evidence for migration, focusing, or significant thickening.

Age-corrected isotopic trends in Cretaceous arc rocks during eastward arc migration are compatible with inheritance of known basement across an oceanic-continental transition; these signals are consistent throughout the Mesozoic CSN [2]. Second-order temporal patterns overprinted on this spatial trend show distinct values during Cretaceous arc activity relative to earlier Triassic and Jurassic flare-ups, including elevated and increased range of Sr/Y and Dy/Yb values, lower Zr/Hf, and higher Rb/Sr values. Together with the restricted range of 87Sr/86Sri,and ƐNd whole-rock isotope values by ca. 85 Ma, this hints at a greater extent of magma differentiation and mixing in the Cretaceous magmatic system. An unresolved spatiotemporal signal is the decoupling of evolved Sr and Nd isotope trends from Pb, O, and Hf juvenile trends at ca. 115 Ma.

In the magmatically distinct Cretaceous arc, dynamic processes occurring throughout the arc column effectively primed the arc lithosphere. This resulted in magma addition rates 6-12 times larger than previous arc flare-ups in the CSN [1]. Dynamic arc behavior has a measurable, secondary influence on the geochemical signals of arc rocks, where spatial and temporal histories can be unraveled.

[1] Paterson et al. (2021). GSA abstract 10.1130/abs/2021CD-363243 [2] Kistler (1990). GSA Mem. 174:271-282