Nd isotopic evidence for enhanced mafic weathering leading to Ordovician cooling

Nd isotopic evidence for the antiquity of the Wyoming province

Sm-Nd isotopic data on Late Archean age metasedimentary rocks from around the Wyoming province yield ENd values at 2.6 Ga from -12.9 to +3.3, which correspond to depleted mantle model ages of 2.7 to 3.8 Ga. These results indicate that crust of a wide variety of ages was exposed and eroding in Late Archean time. The predominance of Middle Archean model ages suggests that continental crust was ex...

High-resolution carbon isotopic records from the Ordovician of South China: Links to climatic cooling and the Great Ordovician Biodiversification Event (GOBE)

What caused the Early Silurian change from mafic to silicic (S-type) magmatism in the eastern Lachlan Fold Belt?

One of the characteristic features of Ordovician tectonism in the east Lachlan Fold Belt is the occurrence of calcalkaline to shoshonitic basalts, which have been recognised as part of an intraoceanic arc environment (Glen et al. 1998), consistent with early tectonic interpretations (Oversby 1971; Scheibner 1973). Aside from typical traceelement abundances of intraoceanic arcs, critical evidenc...

Nd isotopic evidence for transient, highly depleted mantle reservoirs in the early history of the Earth

3870 Ma to 3760 Ma metadiorites and tonalites, and older mafic inclusions contained within these rocks from southern West Greenland, have a range of initial end values from + 4.5 to --4.5. The extremely positive initial values determined for nine of the fourteen early Archean samples demonstra te that they were derived from a LREE depleted mantle reservoir which had an end value of ~ + 4 prior ...

Sm-Nd Isotopic Data and Earth's Evolution.

Samuel A. Bowring and Todd Housh (1) report Sm/Nd isotopic data giving a wide range of initial ENd values, from +3.5 to -4 at 4.0 billion years ago (Ga) and from +4 to -7 at 3.6 Ga. Their samples were from the Acasta gneisses of northern Canada, which represent the oldest known outcrops of continental crust (2). Their modeling of the Sm-Nd isotopic data is taken to suggest that the Acasta grani...