Neoproterozoic magmatic arc assembly in the southern Brazilian Shield – constraints for a plate tectonic model for the Brasiliano orogeny

The characteristics of Archaean greenstone belt terrains are briefly summarized together with some of the models which have been used to account for their genesis. Crystalline sialic crust is interpreted as having increased with time by separation from the mantle. Many of the problems posed by Archaean greenstone belt terrains may be eased if the first sialic crust is assumed to have consisted of small masses concentrated by plate tectonic processes similar to those still in operation. Even if Archaean plates were of similar size, and were formed and lost at rates similar to those since the Mesozoic, there would be differences in the manner in which the sialic crust was concentrated because so little had separated from the mantle during Archaean times. The original formation of the rocks now forming the earliest tonalite gneisses and migmatites is attributed to very early Archaean times when no large sialic concentrations are likely to have existed on subduced lithospheric plates and the only form of orogeny was of the Island Arc type. Even after sialic concentrations did become incorporated in subduced plates they may for a long time have been too small for significant areas to survive extensive remobilization and addition of magmas from below whenever they were associated with plate boundary zones. Sets of greenstone belts are interpreted as vestiges of former oceans. By the end of Archaean times the sialic crustal concentrations, despite possible fragmentation and periods of independent development, became sufficiently extensive for large areas to survive ocean closure without significant remobilization. This model implies that there is no need for orogeny to have been any more extensive in Archaean times than now; it could merely have been more extensive compared to the area of the sialic crust in existence at the time. Plate tectonic models of Archaean tectonics are distinguished from the alternatives by their implication that large relative motions occurred between the oldest parts of the granitoid masses now on either side of the greenstone belts. Palaeomagnetism may be able to distinguish the relative usefulness of the models if any such relative motions can be recognized through the effects of remobilization of most, if not all, the sialic crust in Archaean times. Other tests are possible but the most useful might be the necessity for any model of the formation of the greenstone belts being adaptable enough to account for the relationships emerging from studies of the Archaean crustal remnants characterized by granulite facies metamorphism and anorthosites.

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888–444 Ma Global Plate Tectonic Reconstruction With Emphasis on the Formation of Gondwana

Frontiers in Earth Science ◽

10.3389/feart.2021.666153 ◽

2021 ◽

Vol 9 ◽

Author(s):

Christian Vérard

Keyword(s):

Plate Tectonics ◽

Additional Data ◽

Continuous Process ◽

Tectonic Activity ◽

Plate Tectonic ◽

Sea Floor ◽

Tectonic Model ◽

The Earth ◽

Tectonic Reconstruction ◽

Accretion Rates

The formation of Gondwana results from a complex history, which can be linked to many orogenic sutures. The sutures have often been gathered in the literature under broad orogenies — in particular the Eastern and Western Pan-African Orogenies — although their ages may vary a lot within those wide belts. The Panalesis model is a plate tectonic model, which aims at reconstructing 100% of the Earth’s surface, and proposes a geologically, geometrically, kinematically, and geodynamically coherent solution for the evolution of the Earth from 888 to 444 Ma. Although the model confirms that the assembly of Gondwana can be considered complete after the Damara and Kuunga orogenies, it shows above all that the detachment and amalgamation of “terranes” is a roughly continuous process, which even persisted after the Early Cambrian. By using the wealth of Plate Tectonics, the Panalesis model makes it possible to derive numerous additional data and maps, such as the age of the sea-floor everywhere on the planet at every time slice, for instance. The evolution of accretion rates at mid-oceanic ridges and subduction rates at trenches are shown here, and yields results consistent with previous estimates. Understanding the variation of the global tectonic activity of our planet through time is key to link plate tectonic modeling with other disciplines of Earth sciences.

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