Earth Sciences Seminar: Associate Professor Nathan Daczko

Presenter

Associate Professor Nathan Daczko

Department of Earth and Planetary Sciences

Macquarie University

Associate Professor Nathan Daczko is a metamorphic petrologist who combines field and laboratory studies to examine metamorphic processes. He addresses multiple scales, from microstructure to the evolution of large orogens. Inverting this information provides constraints on the geodynamic and metasomatic processes involved in the history of metamorphic rocks, and advances understanding of crustal evolution and geodynamics.

Abstract

Part 1: Impacts of reactive melt ascent through deep arc crust on melt evolution: recognising and investigating melt migration pathways

The production of continental crust in magmatic arcs is an integral part of plate tectonics and involves the transfer of melt through the lower crust to mid and upper crustal levels. I summarize the different modes of melt transfer recognised in the lower crustal sections of the well-exposed Mesozoic magmatic arc of Fiordland, New Zealand, involving: (1) diffuse and channelized porous melt flow under conditions of low differential stress, (2) syntectonic, channelized porous melt flow and (3) brittle failure allowing melt transfer via dyking.

Each mechanism has distinct field, microstructural and geochemical signatures that can be used to identify them. At the same time these signatures inform about the details of the processes involved. Common to all three mechanisms is the inference that the system is open and that the migrating melt is externally derived. Hence, it is likely to be in chemical disequilibrium with the host rocks through which it migrates.

The chemical potential drives melt-rock reaction and the development of complex microstructures and rock textures. Analogous to aqueous fluid-rock interaction, features typical of reactive transport are common and include reaction fronts, finger structures and rapid replacement of the host assemblage by a distinct, high variance assemblage by dissolution and precipitation.

Part 2: A cryptic Gondwana-forming orogen located in Antarctica

The most poorly exposed and least understood Gondwana-forming orogen lies largely hidden beneath ice in East Antarctica. Called the Kuunga orogen, its interpolation between scattered outcrops is speculative with differing and often contradictory trends proposed, and no consensus on the location of any sutures. 

While some discount a suture altogether, paleomagnetic data from Indo-Antarctica and Australo-Antarctica do require 3000–5000 km relative displacement during Ediacaran-Cambrian Gondwana amalgamation, suggesting that the Kuunga orogen sutured provinces of broadly Indian versus Australian affinity.

Here, compiled and new data from detrital minerals offshore of East Antarctica fingerprint two coastal subglacial basement provinces between 60 and 130°E, one of Indian affinity with dominant ca. 980–900 Ma ages (Indo-Antarctica) and one of Australian affinity with dominant ca. 1190–1140 and ca. 1560 Ma ages (Australo-Antarctica).

This offshore compilation is combined with existing and new onshore mineral isotopic character and previous geophysical interpretations to delimit the Indo-Australo-Antarctic boundary at a prominent geophysical lineament which intersects the coast east of Mirny at ~94°E. This research will lead to improvements in plate tectonic models for the amalgamation of Gondwana.