131 Going with the Shear - New Insights into Lithospheric Extensional and Strike-Slip Systems

This session explores key structural processes that govern the temporal, mechanical, and rheological evolution of crustal/lithospheric extensional and strike-slip systems with a focus on novel field observations, microstructural and analytical methodologies, and numerical modeling.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 217D

The Role of Incremental Melt Injection in Driving Diapiric Flow in Metamorphic Core Complexes

Paper number: 131-4
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

The spatial distribution and tempo of magmatism impact the thermo-mechanical properties of the crust, thereby modulating crustal deformation and rheology. Protracted melt injections are commonly observed within the migmatitic infrastructure of metamorphic core complexes (MCCs), but their role in governing crustal mobility and deformation remains insufficiently quantified. The north-trending Ruby Mountains-East Humboldt Range (REHR) MCC, northeastern Nevada, exemplifies a distinct along-strike gradient in crustal mobility between the mobile infrastructure to the north and unmetamorphosed suprastructure to the south. To quantify the role of incremental melt injection in enhancing crustal mobility in REHR, we present new geologic mapping, zircon U-Pb geochronology, and Raman spectroscopy on carbonaceous material (RSCM) thermometry, along with a synthesis of regional datasets. Our new geologic mapping and geochronology are primarily from the central Ruby Mountains, which marks the transition between the metamorphosed infrastructure and the unmetamorphosed suprastructure. This region marks the southern extent of the infrastructure at the southernmost limit of the Late Cretaceous–Oligocene melt injection complex, coincident with the southernmost exposed kilometer-scale recumbent fold. Regions south of this transition lack penetrative Cenozoic deformation and preserve SE-verging folds associated with Jurassic contractional tectonism, ~15 km-wide Late Jurassic and Late Eocene discrete plutons, and a mostly coherent unmetamorphosed Paleozoic stratigraphic section. A compilation of geochronologic data and field observations along strike of the REHR reveals a strong correlation between protracted melt injection and elevated crustal mobility. Our new along-strike RSCM temperature estimates, together with compiled thermometry data, define a spatially continuous zone of elevated peak temperatures (>600 °C) extending from the East Humboldt range to central Ruby Mountains, consistent with protracted melt injection. To the south of the infrastructure-suprastructure transition, peak metamorphic temperatures gradually decrease, reflecting short pulses of magmatic heating during Jurassic and Eocene pluton emplacement. Based on these observations, we suggest that elevated crustal mobility in the infrastructure is primarily induced by continuous heating (>40 Myr) and melt injection from the Late Cretaceous to Oligocene, which may drive diapiric flow under a reduced density and viscosity condition, particularly during the punctuated heating event during the Eocene–Oligocene Farallon slab rollback. Therefore, the development of the mobile infrastructure of MCCs does not uniquely require large-magnitude extension but may instead be modulated by broader subducting slab dynamics and internal heat redistribution.

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

doi: 10.1130/abs/2025AM-412476

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