74 How are Plutons Made? Physical and Chemical Records of Pluton Construction and Evolution (Posters)

This session integrates structural and petrologic views of plutonic systems, exploring the crustal response to pluton formation, and processes that control the physical and chemical characteristics of pluton-host rock systems from initial emplacement to solidification.

Sunday, 19 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Application of Ti-in-Zircon Thermometry to Track Magma Evolution of the Big Bear Lake Intrusive Suite, Ca.

Paper number: 74-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Big Bear Lake Intrusive Suite (BLIS) is a Late Cretaceous granitic intrusive suite in the Transverse Ranges, Ca., with interest in this suite stemming from its relatively large size (~440 km2) and concentric zonation. Work on the similarly sized (1200 km2) and zoned Tuolumne Intrusive Complex (TIC) has suggested the emplacement of large intrusions in the mid-shallow crust entailed episodic assembly across a protracted period of activity, with most pulses having cooled before the next one intruded. Recent BLIS Pb/U zircon crystallization ages using LA-ICP-MS have a range of ~2 m.y. (from 77.5 to 79.6 Ma), suggesting the BLIS was rapidly assembled, and its units were likely comagmatic. Trace element data were collected from the same zircon spots and this study reports on preliminary Ti-in-zircon thermometry values calculated using the Ferry and Watson 2007 calibration modified by Loucks et al. 2020. Here we use these Ti-in-zircon temperature values and Hf concentrations to examine the magmatic evolution of the BLIS and improve the resolution of our model. Ti-in-zircon temperatures plotted against their Hf concentrations revealed a tight spread for the granodiorite hosted zircons, while the granite hosted zircons spanned a much wider range of temperature and Hf concentration values. We suggest the BLIS was initially emplaced via rapidly stacked sill injections; this early magma chamber homogenized and began crystallizing zircons starting at ~950 °C; zircon crystallization reached its peak productivity from 850 °C until 750 °C when crystal lockup occurred and slowed down zircon crystallization; compaction of these locked up crystals forced the granitic melt to percolate through and concentrate near the top as a lens, allowing for zircon crystallization to continue in this granitic lens until ~650 °C. Future work will include examining zircon spot locations; comparing the zircon compositions to their host rocks; and magma differentiation modeling.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413910

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