Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust

[1] We present an estimate for the composition of the depleted mantle (DM), the source for mid-ocean ridge basalts (MORBs). A combination of approaches is required to estimate the major and trace element abundances in DM. Absolute concentrations of few elements can be estimated directly, and the bulk of the estimates is derived using elemental ratios. The isotopic composition of MORB allows calculation of parent-daughter ratios. These estimates form the “backbone” of the abundances of the trace elements that make up the Coryell-Masuda diagram (spider diagram). The remaining elements of the Coryell-Masuda diagram are estimated through the composition of MORB. A third group of estimates is derived from the elemental and isotopic composition of peridotites. The major element composition is obtained by subtraction of a low-degree melt from a bulk silicate Earth (BSE) composition. The continental crust (CC) is thought to be complementary to the DM, and ratios that are chondritic in the CC are expected to also be chondritic in the DM. Thus some of the remaining elements are estimated using the composition of CC and chondrites. Volatile element and noble gas concentrations are estimated using constraints from the composition of MORBs and ocean island basalts (OIBs). Mass balance with BSE, CC, and DM indicates that CC and this estimate of the DM are not complementary reservoirs.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2003GC000597

Composition of the depleted mantle

Heterogeneous mantle domains: signatures, genesis and mixing chronologies

Petrogenetic evolution of late Cenozoic, post-collision volcanism in western Anatolia, Turkey

Phanerozoic tectonics of the South China Block: Key observations and controversies

http://www2.ess.ucla.edu/~hzou/papers/CG1.pdf

Major, trace element, and Nd, Sr and Pb isotope studies of Cenozoic basalts in SE China: mantle sources, regional variations, and tectonic significance

Theistareykir revisited: THEISTAREYKIR REVISITED

Isotopic evidence for a hotspot origin of the Louisville Seamount Chain

Constraints on the degree of dynamic partial melting and source composition using concentration ratios in magmas

[1] U-Th disequilibrium data on a suite of postglacial basalts ( 30%. The two geochemically and isotopically most depleted samples (picrites) have excess 230Th of about 15%, similar to enriched basalts from locations adjacent to Theistareykir (Draugarhraun and Asbyrgi). The large range in chemical and isotopic variations of the Theistareykir samples provides an excellent opportunity to investigate the influence of source heterogeneity on the degree of U series disequilibrium. The lack of correlation between U-Th data and radiogenic isotope or chemical parameters indicates that source heterogeneity does not play an important role in creating the excess 230Th. Therefore the Theistareykir basalts provide evidence that the Th systematics result from variations in the timing of the melting and melt extraction process only. The relatively large and constant 230Th excesses for the bulk of the Theistareykir samples (20–30%) suggest that melting and melt extraction must be relatively reproducible, with the melting starting well within the garnet-stability field. Near fractional melting models suggest residual porosity ≤0.1%, upwelling rates ≤1cm/yr (corresponding to melting rates ≤1*10−4 kg/m3yr), and melt ascent velocities ≥3–4m/yr. The lower 230Th excesses of about 15% in both the most depleted lavas from Theistareykir and enriched lavas from locations adjacent to Theistareykir (Draugarhraun and Asbyrgi) indicate some variation in the melting and melt extraction process. The low 230Th excesses of the most depleted melts (picrites) could either be an effect of slow melt migration or be caused by incomplete melt aggregation, with melts created at the very bottom of the melting regime being underrepresented. The low 230Th excesses of the most enriched lavas are most likely due to slow melt migration for melts created at some distance from the center of the melting regime.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002GC000347

Alan Zindler

Papers

Major, trace element, and Nd, Sr and Pb isotope studies of Cenozoic basalts in SE China: mantle sources, regional variations, and tectonic significance

Theistareykir revisited: THEISTAREYKIR REVISITED

Isotopic evidence for a hotspot origin of the Louisville Seamount Chain

Constraints on the degree of dynamic partial melting and source composition using concentration ratios in magmas

The dynamics of melting beneath Theistareykir, northern Iceland