Deep continental roots and cratons

Abstract

The formation and preservation of cratons -the oldest parts of the continents comprising over 60% of the continental landmass -remains an enduring problem. Keyto craton development is how and when the thick strong mantle roots that underlie these regions formed and evolved. Peridotite melting residues forming cratonic lithospheric roots mostly originated via relatively low-pressure melting and were subsequently transported to greater depth by thickening produced by lateral accretion and compression. The longest-lived cratons assembled during Mesoarchean and Paleoproterozoic times, creating the 150 to 250 km thick, stable mantle roots that are critical to preserving Earth's early continents and central to defining the cratons although we extend the definition of cratons to include extensive regions of long-stable Mesoproterzoic crust also underpinned by thick lithospheric roots. The production of widespread thick and strong lithosphere via the process of orogenic thickening, possibly in several cycles, was fundamental to the eventual emergence of extensive continental landmasses -the cratons.

Constraints on the Production of Phosphine by Venusian Volcanoes

“…If the mantle is reduced at QIF/IM levels, then iron phosphides become preferred over phosphates at a depth of ~850 km, where the temperature is ~2000 K, which is above the melting temperature of iron phosphides [59]. This is consistent with iron phosphides being dredged from the continental 'keels' of continental cratons on Earth [60] as xenoliths. However, such xenoliths represent milligrams of material in kilograms of rock, not the bulk melt [52,[61][62][63][64][65][66] (hence the name xenolith-"Foreign rock").…”

Heat Generation in Cratonic Mantle Roots—New Trace Element Constraints From Mantle Xenoliths and Implications for Cratonic Geotherms

“…Similarly, heat generation in metasomatized CLM, more typical of the compositions sampled by kimberlite-borne xenoliths (0.006 µW/m 3 ) is significantly lower than past estimates (Figure 8). Although the extent of these lithologies is unknown within the cratonic mantle, we note that sampling bias by melts results in higher proportions of metasomatized lithologies available for study than may be present in CLM and that a portion of the metasomatism in these lithologies is too recent (e.g., Aulbach, Sun, et al, 2017;Pearson & Nowell, 2002;Pearson et al, 2021;Simon et al, 2007) to impact geotherms. Thus, we suggest that 0.006 µW/m 3 is a maximum and unlikely value for heat generation to dominate bulk CLM.…”

Modification of Lithospheric Mantle by Melts/Fluids With Different Sulfur Fugacities During the Wilson Cycle: Insights From Lesvos and Global Ophiolitic Peridotites

“…Despite the potential for metasomatism to disturb the Re-Os isotopic system, its robustness as a tracer of mantle melting events is validated by those samples preserving ancient melting information (e.g., Brandon et al, 2000;Pearson et al, 2007Pearson et al, , 2021Rudnick & Walker, 2009). For the ophiolitic peridotites from different settings we compiled, they all have a tail of unradiogenic 187 Os/ 188 Os, corresponding to a cluster of T RD ages at 1.6-2.0 Ga (Figure 8)-a signature originally identified in Pt-group alloys from ophiolites (Pearson et al, 2007).…”