Chalcophile element (Cu, Zn, Pb) and Ga distribution patterns in ancient and modern oceanic crust and their sources: Petrogenetic modelling and a global synthesis

Furnes, Harald; Dilek, Yildirim; Kiseeva, Ekaterina S.

Chalcophile element (Cu, Zn, Pb) and Ga distribution patterns in ancient and modern oceanic crust and their sources: Petrogenetic modelling and a global synthesis

dc.contributor.author	Furnes, Harald
dc.contributor.author	Dilek, Yildirim
dc.contributor.author	Kiseeva, Ekaterina S.
dc.date.accessioned	2022-06-20T14:49:09Z
dc.date.available	2022-06-20T14:49:09Z
dc.date.issued	2022-05-18
dc.date.updated	2022-06-20T14:31:01Z
dc.description.abstract	We present a global synthesis of Cu, Zn, Pb and Ga contents of mafic dike complexes and volcanic rocks associated with 259 ophiolites, ranging in age from Archaean throughout the Phanerozoic. These ophiolites are geochemically classified as subduction-unrelated and subduction-related with various sub-categories, as defined in Dilek and Furnes (2011). The subduction-unrelated ophiolites include Mid-Ocean Ridge (MOR), and Rift, Continental Margin and Plume type ophiolites, collectively grouped as the R/CM/P sub-category. The subduction-related ophiolites include Backarc (BA), Forearc (FA), Backarc to Forearc (BA-FA), and Volcanic Arc (VA) sub-categories. Compositional distribution of these elements in different ophiolite sub-categories show that Zn and Ga patterns are largely uniform and unrelated to the tectonic setting, whereas Cu and Pb patterns show significant variations. Average copper concentrations progressively increase from subduction-related ophiolites to R/CM/P and MOR. Although less pronounced, lead shows a similar increase in average concentrations from subduction zone environments to MOR, with rather irregular patterns for the R/CM/P and VA types. Mafic subunits in analysed ophiolites define similar trends for Cu and Pb. The mafic subunits, comprising alkaline basalts, mid-ocean ridge basalts (MORB), island arc tholeiites (IAT) and boninites, define a progressive shift towards increasing proportions of low concentrations of Cu and Pb in the listed order. To constrain the large variations in the contents of the given elements, we applied petrogenetic modelling of glass analyses. Petrogenetic modelling of the MgO versus Cu, Zn, Pb and Ga distributions in modern MORB show a scatter that can be explained by different degrees of fractional crystallization (20 – 80%) of primitive MORB lavas. In support of previous studies, we find that most erupted MORB lavas are sulphur saturated, whereas primitive boninitic and IAT magmas are S-undersaturated. The trends observed for IAT are in agreement with previous findings that IAT precipitate sulphide only at very high degrees of fractional crystallization, owing to crystallization of magnetite. Boninites are variable and Cu concentration in boninitic glasses indicates that a fraction of them may be S-saturated at relatively low degrees of fractional crystallization. We model two boninitic compositions and achieve S saturation at 15 and 50% fractional crystallization. The observed Pb enrichment in the R/CM/P ophiolites was likely caused by crustal contamination. Mantle sources of mafic magmas of the ophiolites were also enriched in Cu and Pb by a combination of subduction-related processes as reflected in the chalcophile element (Cu and Pb) behavior patterns of various mafic rock types in the ophiolites. Comparing with in-situ oceanic crust, we conclude that the chalcophile element distribution patterns of Cu, Zn, Pb and Ga in mafic lavas and dikes in ophiolites were ca. 80–90% magmatically controlled by their abundances in the mantle melt sources, partial melting episodes, and extents of fractional crystallisation processes. The remaining 10–20% difference we attribute mainly to alteration processes (predominantly loss), as well as types and amounts of subducted sediments, whose melt products contributed to the melt column above subducting slabs.	en
dc.description.status	Peer reviewed	en
dc.description.version	Accepted Version	en
dc.format.mimetype	application/pdf	en
dc.identifier.citation	Furnes, H., Dilek, Y. and Kiseeva, E. S. (2022) 'Chalcophile element (Cu, Zn, Pb) and Ga distribution patterns in ancient and modern oceanic crust and their sources: Petrogenetic modelling and a global synthesis', Gondwana Research, 109, pp. 394-415. doi: 10.1016/j.gr.2022.05.008	en
dc.identifier.doi	10.1016/j.gr.2022.05.008	en
dc.identifier.endpage	415	en
dc.identifier.issn	1342-937X
dc.identifier.journaltitle	Gondwana Research	en
dc.identifier.startpage	394	en
dc.identifier.uri	https://hdl.handle.net/10468/13303
dc.identifier.volume	109	en
dc.language.iso	en	en
dc.publisher	Elsevier B.V.	en
dc.rights	© 2022, International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. This manuscript version is made available under the CC BY-NC-ND 4.0 license.	en
dc.rights.uri	https://creativecommons.org/licenses/by-nc-nd/4.0/	en
dc.subject	Chalcophile elements	en
dc.subject	Cu and Pb enrichment	en
dc.subject	Fractional crystallization	en
dc.subject	Ophiolite types	en
dc.subject	Partial melting	en
dc.subject	Slab effects	en
dc.title	Chalcophile element (Cu, Zn, Pb) and Ga distribution patterns in ancient and modern oceanic crust and their sources: Petrogenetic modelling and a global synthesis	en
dc.type	Article (peer-reviewed)	en