REVISITING PLUTON EMPLACEMENT THROUGH THE LENS OF INCREMENTAL GROWTH; NEW OPPORTUNITIES FOR EVALUATING THE ENTIRE PLUTON-HOST ROCK SYSTEM IN ASYMMETRICAL INTRUSIONS

The incremental growth of intrusive complexes increases the potential of distorted or lost information by overprinting and recycling of magmatic and host rock materials. Detailed studies of incremental host rock histories are rare, despite the implication that incremental growth requires incremental host rock displacement. Asymmetrical and migrated intrusions are ideal for unraveling overprinting relationships in plutonic and host rock units because their geometries effectively limit the number of components in pluton-host rock system to only one or two plutonic units or pulses at a time. The pulses intrude adjacent to one another and often minimally distort previous features. In composite, nested bodies, re-intrusion in the center of the body often makes connecting the timing and rates of host rock and pluton deformation to specific intrusive events challenging.

The following processes are likely to be better preserved in asymmetrical and migrated systems and can be leveraged to study the incremental evolution of pluton-host rock systems: 1) pulses develop separate local thermal and structural aureoles that create compound aureoles where the units partially overlap; 2) evolving material transfer processes that result from a maturing thermal gradient are discretely preserved as changes to structural markers associated with a given pulse; 3) magmatic pulses may intrude a broad or narrow range of host rock lithologies, preserving how different host lithologies respond to magmatism; 4) units may span a range of volatile compositions and concentrations, resulting in locally distinct host rock metamorphism and capturing how volatiles and host rocks interact as growth proceeds; and 5) map patterns allow for confident reconstructions of original unit geometries. Geometries can be coupled with high-precision geochronology to constrain durations and rates of magma addition, host rock displacement, pluton cooling, magma chamber longevity, and physical and chemical interactions between pulses.

Leveraging these relationships in asymmetrical intrusive complexes, we can refine constraints for thermal, physical, and chemical models of these systems. Integration across these domains is needed for understanding the multiple structural and chemical roles of transcrustal magmatic systems in hot orogens.