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Highly siderophile elements mobility in the subcontinental lithospheric mantle beneath southern Patagonia

Tassara, Santiago; González-Jiménez, José M.; Reich, Martin; Saunders, Edward; Luguet, Ambre; Morata, Diego; Grégoire, Michel; van Acken, David; Schilling, Manuel E.; Barra, Fernando; Nowell, Geoff; Corgne, Alexandre

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Santiago Tassara

José M. González-Jiménez

Martin Reich

Edward Saunders

Ambre Luguet

Diego Morata

Michel Grégoire

David van Acken

Manuel E. Schilling

Fernando Barra

Alexandre Corgne


Peridotite xenoliths collected from alkali basalts in the Argentinian Patagonia reveal the existence of an ancient depleted Paleoproterozoic mantle that records a subsequent multistage metasomatic history. Metasomatism is associated with carbonatite-like melts that evolved, after variable melt/rock ratio interaction, towards CO2-rich and Na-bearing Mg-rich (mafic) silicate, and volatile-rich alkali silicate melts. High degrees of partial melting produced strongly depleted mantle domains devoid of base-metal sulphides (BMS). Moderate degrees of partial melting and later unrelated metasomatism produced a range of slightly depleted, slightly enriched, and strongly enriched mantle domains that preserve different types of BMS. Thus, six different BMS populations were identified including typical residual Type 1A BMS enriched in Os, Ir, and Ru relative to Pt, Pd, and Au located within primary olivine and clinopyroxene, and metasomatic Type 2A BMS that are relatively enriched in Pt, Pd, Au occurring as interstitial grains. Reworking of these two types of BMS by later metasomatism resulted in the formation of a new generation of BMS (Type 1B and Type 2B) that are intimately associated with carbonate/apatite blebs and/or empty vesicles, as well as with cryptically metasomatised or metasomatic clinopyroxene. These newly formed BMS were re-enriched in Os, Pd, Au, Re and in semi-metal elements (As, Se, Sb, Bi, Te) compared to their Type 1A and Type 2A precursors. A third generation of BMS corresponds to NiCu immiscible sulphide mattes entrained within Na-bearing silica under-saturated alkali melt. They occur systematically related to intergranular glass veins and exhibit distinctively near flat CI-chondrite normalised highly siderophile element patterns with either positive Pd (Type 3A) or negative Pt (Type 3B) anomalies. Our findings indicate that Os, Pd, Re and Au can be selectively transported by volatile-rich alkali silicate melts in the subcontinental lithospheric mantle. Moreover, the transport of sulphide mattes entrained in silicate melts is also an effective mechanism to produce HSE endowment in the SCLM and play an important role as precursors of fertile, metal-rich magmas that form ore deposits in the overlying crust.

Journal Article Type Article
Acceptance Date Jun 24, 2018
Online Publication Date Jul 5, 2018
Publication Date Aug 1, 2018
Deposit Date Jul 10, 2018
Publicly Available Date Jan 3, 2024
Journal Lithos
Print ISSN 0024-4937
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 314-315
Pages 579-596
Public URL


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