FOZO, HIMU, and the rest of the mantle zoo

Abstract

[1] The parameter m describes the 238 U/ 204 Pb ratio of an Earth reservoir. Mantle domains labeled HIMU (high m) originally defined reservoirs with highly radiogenic Pb isotope ratios observed in basalts from a select number of ocean islands, St. Helena in the Atlantic Ocean and the Cook-Austral islands in the South Pacific Ocean. While some authors use the term HIMU in this original sense, others refer to HIMU as a widespread component in many mid-ocean ridge and ocean island basalt (MORB and OIB) sources. Here we show that highly radiogenic Pb isotope signatures in MORB and OIB originate from two different sources. In addition to the classical HIMU component observed at St. Helena and the South Pacific (named HIMU in the following), we define a component with slightly less radiogenic Pb but significantly more radiogenic Sr isotope signatures. This component lies at the extension of the (Atlantic and Pacific) MORB array in a Sr-Pb isotope ratio diagram and is argued to be a ubiquitous component in MORB and many OIB sources. The inferred role of this component in the mantle and its inferred genetic origin closely resemble those originally suggested for a mantle component termed FOZO by Hart and coworkers. By redefining the composition, the origin, and the role of FOZO in the mantle, we establish a simple conceptual framework that explains the isotopic variability in both MORB and OIB with the lowest number of components. OIB are grouped into HIMU-type OIB and basalts from islands that diverge from the MORB-FOZO array toward various isotopically ''enriched'' compositions (EM). The apparent ubiquity of FOZO in the mantle and the calculated isotopic evolution of compositionally diverse MORB suggest that normal mantle melting and continuous subduction and aging of that crust during recycling through the mantle are the dominant causes of the MORB-FOZO array. In contrast to FOZO, HIMU-type OIB are quite rare, and if an origin by recycling of oceanic crust is also postulated, the production of HIMU sources has to be a special and rare combination of age and composition of subduction-modified recycled oceanic crust.

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

“…EC is assumed to have nine times more Pb, three times more La, and an equivalent amount of Sm and Na2O relative to McDonough and Sun's [1995] primitive mantle. EC's 206 Pb/ 204 Pb ratio of 20.3 is similar to the "FOZO" component of Stracke et al [2005] (i.e., 20.0). The veins of EC are assumed to make up (ø 2 =) 10% of the mantle and the DC matrix makes up the remaining (ø 1 =) 90%.…”

Mantle convection and evolution with growing continents

“…Parman [2007] shows that the MORB contribution to CC generation dominates in the Phanerozoic while the OIB contribution prevails in the main preceding part of the mantle's evolution. This is the background for why we based our convection -fractionation model, particularly the geochemical part, on the more recently developed reservoir models by Hofmann [2003], Stracke et al [2005], and Willbold and Stracke [2006] (cf. section 1.1).…”

“…For example, Stracke et al [2005] and Willbold and Stracke [2006] propose a new FOZO similar to the traditional FOZO except that this new FOZO is a small-scale component, ubiquitously dispersed throughout the entire mantle. The exact definition of FOZO can be found in Hart et al [1992].…”

Origin and evolution of Cenozoic magmatism of Sardinia (Italy). A combined isotopic (Sr–Nd–Pb–O–Hf–Os) and petrological view

“…The basalts of this island, together with those from other few localities in French Polynesia (Rurutu and Rarotonga islands; SW Pacific Ocean) define the HIMU-OIB type-locality, one of the geochemical end-member of the mantle "zoo", believed to represent ancient, recycled oceanic crust (Zindler and Hart, 1986;Stracke et al, 2005;White, 2010;Stracke, 2012 87 Sr/ 86 Sr), which is generally considered to reflect the involvement of terrigenous sediments in mantle sources. Given the evolved nature of the RPV rocks (eight out of eleven samples having MgO <3 wt%) we believe that their isotope-isotope and isotope-SiO 2 -MgO correlations reflect some degrees of interaction with local upper crust, represented by Hercynian granitoids, rather than mantle source contamination.…”