Phonolitic melt production by carbonatite Mantle metasomatism: evidence from Eger Graben xenoliths

Causes and Consequences of Wehrlitization Beneath a Trans‐Lithospheric Fault: Evidence From Mesozoic Basalt‐Borne Wehrlite Xenoliths From the Tan‐Lu Fault Belt, North China Craton

“…In summary, consistent with observations from wehrlite xenolith suites from many other localities, the majority of wehrlites in this study are ascribed to melt‐rock interaction at high melt/rock ratios, during which silica‐undersaturated melts replaced Opx with Cpx and increased Fe contents in whole rock (Aulbach et al, 2017; Ionov et al, 2005; Loges et al, 2019; Shaw et al, 2018; Xiao et al, 2010; Xu et al, 1996; Yaxley et al, 1991), in a process referred to as “wehrlitization” (e.g., Chakraborti et al, 2018; Kogarko et al, 2001). Such metasomatic wehrlitic mineral assemblages have been reproduced in high‐temperature and high‐pressure experiments, where primary peridotites react with carbonate‐rich melts of different compositions (Gervasoni et al, 2017; Green & Wallace, 1988; Yaxley et al, 1998).…”

“…Wehrlites can be used to probe into melt‐rock reactions or deep magmatic processes, depending on their genesis, thus being an important ultramafic lithology in many mantle sections (e.g., Chin, 2018; Loges et al, 2019; Shaw et al, 2018; Xu et al, 1996). This lithology can be found in different tectonic settings all over the world, such as intraplate setting, active rift zones, and orogenic belts (e.g., Ackerman et al, 2009; Ishiwatari, 1985; Xiao et al, 2010).…”

Wehrlites from continental mantle monitor the passage and degassing of carbonated melts

“…The higher melt volumes involved in the generation of SiO 2 -rich melts may therefore compensate for their lower CO 2 contents in terms of their ability to convert a given amount of orthopyroxene to clinopyroxene. The link between silica-undersaturated carbonated melts, wehrlites and decarbonation at low pressure is strengthened by direct observations of CO 2 -rich fluid inclusions, carbonates, carbonatebearing glass veins and melt pockets in wehrlites, with entrapment pressures of 0.8 to 1.7 GPa (e.g., Yaxley et al, 1998;Loges et al, 2019). It is further supported by experimental studies which show that wehrlite forms in equilibrium with carbonated melts (Yaxley and Green, 1996;Gervasoni et al, 2017).…”

Trachytic Melt Inclusions Hosted in Clinopyroxene Offer a Glimpse Into Samoan EM2‐Endmember Melts

“…(2020) performed an analysis of water systematics and major and trace element characteristics in Samoa peridotite xenoliths (focusing on orthopyroxenes) revealing variable depletions in water contents of nominally anhydrous minerals, and in addition to their trace element characteristics, indicate metasomatism of carbonatitic and silicate liquids. Further, previous studies have suggested that partial melting of mantle enriched with carbonatitic liquids can result in phonolitic to trachytic liquids (Ashwal et al., 2016; Hauri et al., 1993; Loges et al., 2019; Tsuno and Dasgupta, 2011). To this end, Hauri et al.…”

“…More recently, Ashley et al (2020) performed an analysis of water systematics and major and trace element characteristics in Samoa peridotite xenoliths (focusing on orthopyroxenes) revealing variable depletions in water contents of nominally anhydrous minerals, and in addition to their trace element characteristics, indicate metasomatism of carbonatitic and silicate liquids. Further, previous studies have suggested that partial melting of mantle enriched with carbonatitic liquids can result in phonolitic to trachytic liquids (Ashwal et al, 2016;Hauri et al, 1993;Loges et al, 2019;Tsuno and Dasgupta, 2011). To this end, Hauri et al (1993) found trachytic glass (69% SiO 2 , 8% total alkalis; see main text Figures 3-6 for plotted compositions of the glass) hosted in a carbonatite metasomatized peridotite xenolith from the Samoan island of Savai'i-the same volcano that erupted the ALIA-D115-18 melt inclusions examined here-which they interpret to be the product of a reaction between carbonatitic melt with peridotite.…”