Titanium isotope evidence for the high topography of Nuna and Gondwana - Implications for Earth’s redox and biological evolution

Titanium isotopes recorded in glacial diamictites with depositional ages between 2.9 and 0.3 Ga show that the upper continental crust became significantly more felsic relative to the present-day crust during the amalgamation of the Paleoproterozoic Nuna and the Neoproterozoic Gondwana supercontinents. This can be attributed to the continental collisions involved in the assembly of Nuna and Gondwana. The resulting high topographic relief of Nuna and Gondwana orogens must have resulted in an enhanced erosional supply from the continents to oceans. The step changes in the development of organismal complexity from prokaryotes to eukaryotes, and eventually metazoans, appear to be temporally correlated to instances where collisional mountain-building sustained an elevated nutrient supply from the continents to oceans. The nutrient surge associated with the rise of the Gondwana mountains likely provided the necessary impetus for the Neoproterozoic ecological expansion of eukaryotes and the eventual radiation of metazoans. A similar link between the enhanced nutrient supply from Nuna mountains and the radiation of early eukaryotes is plausible, although its mechanistic underpinnings remain unclear. The termination of Nuna orogeny and its transition to Rodinia without significant breakup and subsequent collisional orogenesis corresponds to the long lull in Earth's redox and biological evolution in its middle age

Isotopic evolution of the Idaho batholith and Challis intrusive province, northern US cordillera

The Idaho batholith and spatially overlapping Challis intrusive province in the North American Cordillera have a history of magma-tism spanning some 55 Myr. New isotopic data from the 98Ma to 54Ma Idaho batholith and51Ma to 43Ma Challis intrusions, coupled with recent geochronological work, provide insights into the evolution of magmatism in the Idaho segment of the Cordillera. Nd and Hf isotopes show clear shifts towards more evolved compositions through the batholith’s history and Pb isotopes define distinct fields correlative with the different age and compositionally defined suites of the batholith, whereas the Sr isotopic compositions of the various suites largely overlap.The subsequent Challis magmatism shows the full range of isotopic compositions seen in the batholith.These data suggest that the early suites of metaluminous magmatism (98^87 Ma) represent crust^mantle hybrids. Subsequent voluminous Atlanta peraluminous suite magmatism (83^67 Ma) results pri-marily from melting of different crustal components. This can be attributed to crustal thickening, resulting from either subduction pro-cesses or an outboard terrane collision. A later, smaller crustal melt-ing episode, in the northern Idaho batholith, resulted in the Bitterroot peraluminous suite (66^54 Ma) and tapped different crustal sources. Subsequent Challis magmatism was derived from both crust and mantle sources and corresponds to extensional collapse of the over-thickened crust