TY - JOUR
T1 - Highly siderophile elements mobility in the subcontinental lithospheric mantle beneath southern Patagonia
AU - Tassara, Santiago
AU - González-Jiménez, José M.
AU - Reich, Martin
AU - Saunders, Edward
AU - Luguet, Ambre
AU - Morata, Diego
AU - Grégoire, Michel
AU - van Acken, David
AU - Schilling, Manuel E.
AU - Barra, Fernando
AU - Nowell, Geoff
AU - Corgne, Alexandre
N1 - Corrigendum exists for this article and can be found in Lithos, 316-317, p.407, doi: 10.1016/j.lithos.2018.07.021
PY - 2018/8
Y1 - 2018/8
N2 - 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 Ni-Cu 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.
AB - 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 Ni-Cu 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.
KW - Subcontinental lithospheric mantle
KW - Metasomatism
KW - Mobility
KW - Highly siderophile elements
KW - Base-metal sulphides
UR - http://www.scopus.com/inward/record.url?scp=85049742765&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/record.url?scp=85050982502&partnerID=8YFLogxK
UR - https://doi.org/10.1016/j.lithos.2018.07.021
U2 - 10.1016/j.lithos.2018.06.022
DO - 10.1016/j.lithos.2018.06.022
M3 - Article
SN - 0024-4937
VL - 314-315
SP - 579
EP - 596
JO - Lithos
JF - Lithos
ER -