Evolution of geodynamics since the Archean: Significant change at the dawn of the Phanerozoic

Abstract

A time-series analysis of thermobaric ratios (temperature/pressure [T/P]) for Paleoarchean to Cenozoic metamorphic rocks identified significant shifts in mean T/P that may be related to secular change in the geodynamics on Earth. Thermobaric ratios showed significant (>95% confidence) change points at 1910, 902, 540, and 515 Ma, recording drops in mean T/P, and at 1830, 604, and 525 Ma, recording rises in mean T/P. Highest mean T/P occurred during the Mesoproterozoic, and lowest mean T/P occurred from the Cambrian to the Oligocene. Correlated changes were seen between T/P and global data sets of time-constrained hafnium (Hf) and oxygen (O) isotope compositions in zircon. The range of correlated variation in T/P, Hf, and O was larger during the formation of Rodinia than Columbia. Large changes and a wide range for these variables continued through the Phanerozoic, during which a statistically significant 83 m.y. frequency of T/P excursions recorded the high tempo of orogenic activity associated with the separation, migration, and accretion of continental terranes during the formation of Pangea. Since the early Tonian, the decreasing mean T/P of metamorphism, widespread appearance of blueschist and ultrahigh-pressure metamorphism, and wide fluctuations in Hf and O isotope compositions document a change to the modern plate-tectonic regime, characterized by widespread continental subduction and deeper slab breakoff than in the Proterozoic.

Widespread reworking of Hadean-to-Eoarchean continents during Earth’s thermal peak

“… 25 ) locally weighted scatterplot smoothing 26 curves with bootstrapped uncertainties that allow interrogation of the second-order variations (i.e., excluding first-order planetary differentiation, e.g., ref. 27 ). Bins with less than five data points are considered to have too few data points to be robust and are excluded from consideration, though their inclusion results in no significant difference to the fit.…”

The Mesoproterozoic Single-Lid Tectonic Episode: Prelude to Modern Plate Tectonics

“…A second line of positive evidence is that the lithosphere heated up. This is shown by the metamorphic thermobaric ratios (temperature/pressure, T/P) for Paleoarchean to Cenozoic metamorphic rocks (Brown et al, 2020). Thermobarometric ratios over the past 3.0 Ga are highest for Mesoproterozoic time (Fig.…”

“…"Boring Billion" from Holland (2006). Single-lid tectonic indicators include (E) A-type granites (Condie, 2014), (F) massif-type anorthosites (Ashwal, 2010), (G) thermobarometric ratios (n = 564; best fit curve from Brown et al, 2020), and (H) numbers of passive continental margins (Bradley, 2011). Fourfold confidence subdivision of Bradley (2011) is simplified into two intervals of higher and lower confidence.…”

Extending full-plate tectonic models into deep time: Linking the Neoproterozoic and the Phanerozoic

“…and subduction of oceanic crust in the Neoproterozoic was fundamentally similar to the Cenozoic. We note that this may not be a valid assumption for the early Neoproterozoic, since abundant ophiolite preservation only occurs after Rodinia breakup (Stern and Miller, 2018) and pre-1 Ga ophiolites suggest thicker oceanic crust (Moores, 2002) which, along with secular changes in Earth's heat loss (Brown et al, 2020b) could have an influence on spreading and subduction dynamics. Nonetheless, we maintain that if available palaeomagnetic and geological data can be reconciled within a uniformitarian framework of oceanic crust production and destruction, then our model becomes a useful reference model for future models that explore alternative hypotheses.…”