168-2 The Thermal Legacy of Pannotia Amalgamation

Session: Laurentia Without Borders: Pre-Pangea Intercontinental Connections

Presenting Author:

Authors:

Abstract:

The existence of the putative late Neoproterozoic supercontinent Pannotia (Gondwana + Laurentia + Baltica + Siberia) is controversial. It is generally agreed that the Gondwanan portion of Pannotia was assembled by Pan-African collisional orogens with final assembly between 520 and 490 Ma. The main geodynamic issue is whether this assembly changed global-scale mantle convection patterns because such changes would need to be incorporated into geodynamic models for the assembly of Pangea.

Evidence of major changes in mantle circulation in the aftermath of Gondwana assembly includes widespread (i) plume-related magmatism around Gondwana’s periphery, (ii) ironstone deposits related to mantle plume-ocean ridge interaction and enhanced hydrothermal activity, and (iii) super-mature clastic deposits that reflect epeirogenic uplift triggered by mantle upwelling beneath Gondwana combined with deep tropical weathering.

In our model, Gondwana assembled above a region of mantle downwelling in which subducted slabs between the converging Gondwanan continents descended to the core-mantle boundary. Renewed subduction along Gondwana’s periphery yielded early arc magmas. As the downwelling beneath Gondwana evolved into an upwelling, mantle plumes rose and interacted with the edges of Gondwana, where they penetrated the peripheral subduction zones via slab windows, tears and transform faults to generate voluminous calc-alkalic crustal melts in hydrated arc regions and A-type magmas in dry back-arc regions. The plumes also underplated oceanic lithosphere and interacted with adjacent ocean ridges, thereby enhancing hydrothermal activity leading to the recurrence of marine iron-rich sedimentary rocks in the geological record. At the same time, upwelling beneath sub-tropical Gondwana led to epeirogenic uplift, deep weathering and erosion, resulting in the production of widespread super-mature clastic deposits. Global-scale changes in mantle convection patterns should be incorporated into geodynamic models for Pangea.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5475

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