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6th International Archean Symposium
6th International Archean Symposium

The extent of Archean lithosphere on Proterozoic terranes as from evidence by multiple geoscientific proxies.

Oral

Talk Description

The construction and preservation of the lithosphere throughout the Archean and Proterozoic eons occurred through geological processes that often obliterate evidence sets for its affiliation and extent, making the record difficult to unfold. To do so often requires using complimentary evidence acquired across different spatial and temporal scales from field observations, geochemistry including absolute dating and isotopic studies, and geophysical methods covering different physical properties and depths. We present an overview of recent, large-scale studies employing multiple geoscientific proxies to unfold the evolution of exposed Archean lithosphere and Proterozoic or younger crustal sections withholding relationships to it. Multi-proxy studies carried out on Archean-Proterozoic lithosphere point out to a recurrent disconnect between the actual exposure of Archean-Proterozoic cratonic crust and the extent of their corresponding lithospheric keels. The combined use of seismology and seismic, magnetotelluric and potential field data, and geochemistry shows that Archean substrate often has an extended footprint below Proterozoic to younger successions (e.g., Kalahari and Kaapvaal-Zimbabwe, Amazonian, Gawler, Karelian and Sao Francisco cratons). In contrast, some cratonic sections have in-depth footprints in seismology and potential field data that are far smaller than the exposed cratonic core crust (e.g., Angola, Tanzania, and Norrbotten cratons). The case for absence of an anticipated Archean framework in the intervening region to the (Proterozoic) North-, West- and South Australia cratons has been brought up via combined study of the U-Pb-O-Hf isotope systems on zircon and seismic studies. The comprehensive study of the chemical content on ferromagnesian silicates and base metal sulphides - major elements, trace and base metals, Re-Os isotope chemistry - on lithospheric mantle xenoliths hosted on Quaternary volcanics in Central Mexico point out to the presence of a cryptic sub-lithospheric continental mantle root of Archean-Proterozoic age confined by Paleozoic-Mesozoic sutures. Furthermore, cases exist of key mineral deposit types and their relative abundance being observably limited to either pristine or recycled Archean lithosphere. The persistence and evolution of Archean lithosphere can be tracked through spatial and temporal scales with a multitude of geoscientific tools to expose facets of the record and provide hints to the involved geological processes. The over-arching effect of the presence, absence of, and recycling of Archean cratonic lithosphere seems to be that of affecting the lithosphere’s stability or susceptibility to transformation on subsequent stages, imprinting certain chemical and mechanical characteristics either on their crustal volumes or lithospheric roots. However, no clear picture exists over either the processes that promote cratonic lithospheric growth and their demise in both the past and present. In a wholistic view, it becomes clear that Archean lithospheric somehow persists in the record although a definitive spatial-temporal blueprint is yet to be defined.

Speakers