22 Evolution of Cordilleran-type orogenic systems (Posters)

This session seeks contributions that connect surface, crustal, and mantle processes associated with Cordilleran systems, specifically addressing geodynamics, kinematics, magmatism, uplift, erosion, basin subsidence, and sediment dispersal in ancient and modern settings.

Thursday, 23 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Mapping frictional melt dynamics at the millimeter scale with mini-AMS

Paper number: 22-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The anisotropy of magnetic susceptibility (AMS) measures preferred mineral alignment in igneous rocks. AMS fabrics record magma-induced strain, allowing reconstruction of flow directions, intensity, and kinematics. Applied across intrusions, AMS maps internal viscous flow patterns, revealing emplacement mechanisms, conduit geometry, and temporal evolution during solidification at multiple scales and structural levels within. Recent methodological developments now allow measurement of AMS on 3.5-millimeter specimens using high-sensitivity instruments. Smaller samples permit dense spatial sampling, reduce material requirements, and allow analysis of very small melt bodies, while providing reliable magnetic fabric information comparable to standard 1-inch cores for flow and strain mapping. Using smaller AMS samples is well suited for pseudotachylytes because their very fine grain size promotes homogeneous magnetic fabrics, and their typically high magnetic susceptibility ensures strong magnetic fabric intensity. Pseudotachylytes show that faults can experience extremely high frictional heating at the onset of slip, followed by rapid dynamic weakening due to melt lubrication, hence capturing the thermal and mechanical signature of real earthquakes. This approach allows reliable AMS measurements from 3.5-millimeter specimens, enabling detailed fabric analysis in thin fault-related melt veins. I present recent results from the Santa Rosa Mountains, California highlighting the underexplored potential of the mini-AMS method when applied to generation veins, injection veins, melt reservoirs and complex vein geometries.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410893

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