Geochemistry and mantle source characteristics of the Itasy volcanic field: Implications for the petrogenesis of basaltic magmas in intra-continental-rifts

Cenozoic Dynamic Topography of Madagascar

“…In the Central Highlands, the Ankaratra province is characterized by nephelinites, basanites, and tholeiitic basalts as well as more evolved trachytes and phonolites (e.g., Cucciniello et al., 2011). Here, K‐Ar dates range from 27.9 to 2.86 Ma, and Ar‐Ar dates range from 17.45 to 0.031 Ma (Bardintzeff et al., 2010; Buchwaldt, 2006; Cucciniello et al., 2017; Melluso et al., 2016; Rasoazanamparany et al., 2021). In the southwest, Ankililoaka consists of scattered plugs, lava flows, and scoria cones of basanite and alkali basalt with Ar‐Ar ages ranging from 12.03 to 10.55 Ma (Cucciniello et al., 2018).…”

“…This phase of extension is manifest by northeast-southwest oriented troughs filled with Neogene sedimentary rocks, which are now regarded as part of the East African Rift system (Kusky et al, 2010;Saria et al, 2014;Stamps et al, 2021). In post-Oligocene times (i.e., ∼23 Ma-Recent), mafic magmatism occurred in central, southern, and northern parts of Madagascar (Figure 2d; Bardintzeff et al, 2010;Cucciniello et al, 2017Cucciniello et al, , 2018Emerick & Duncan, 1982;Estrade et al, 2014;Melluso et al, 2011Melluso et al, , 2016Rasoazanamparany et al, 2021). Monogenetic lava fields, stratovolcanoes, and dyke swarms were first described by Lacroix (1915) and have since been attributed variously to rift magmatism resulting from lithospheric thinning to emplacement of a mantle plume (Cucciniello et al, 2017;de Wit, 2003).…”

Petrogenesis of Lava from Christmas Island, Northeast Indian Ocean: Implications for the Nature of Recycled Components in Non-Plume Intraplate Settings

“…However, the UVS Os abundances all fall below the recommended value of 50 ppt for uncontaminated lava from the Canary and Madeira Islands [79,80]. ; Reunion [82][83][84]; Kerguelen [85]; Samoa [86,87]; Pitcairn [66]; Austral [82,88]; Austral-Cook [89]; Madagascar [74]. The horizontal dotted line at Os 50 ppt is the proposed cut off filter [79] to eliminate crustally contaminated lavas.…”

“…Delta (∆) values measure the vertical deviation in 207 Pb/ 204 Pb or 208 Pb/ 204 Pb from a northern hemisphere reference line (NHRL, solid vertical and horizontal lines at 0 in (a)) as defined by [36]. Symbols, lines and data fields as follows: Grey vertical line at ∆ 208 Pb/ 204 Pb = 60 is after [43] who define DUPAL hotspot lava with ∆ 208 Pb/∆ 204 Pb >60, with 87 Sr/ 86 [73]); r-SCLM (refractory subcontinental lithospheric mantle; [74]); CHRISP fields [10] as follows: CKP-Cocos/Keeling Province; EWP-Eastern Wharton Province; VMP-Vening-Meinesz Province; AP-Argo Province; Japan Trench [75]; Uo Mamae [61,62]; Reunion (average n = 70 analyses from Piton de la Fournaise; [58]); Kerguelen (Heard Island, average for the Big Ben lava series; [57]); DMM-206 Pb/ 204 Pb and 207 Pb/ 204 Pb values from [76]) and 208 Pb/ 204 Pb values from [77]; HIMU-average (n = 14) >9 wt% MgO lava from Mangaia Island [64]; EM1-average (n = 11) > 9 wt% MgO lava from Pitcairn Island and adjacent seamounts [65,66]; EMII-average (n = 6) >9 wt% MgO lava from Savaii Island, Samoa [67]; Component-"C" [78].…”

“…Applying such a filter to the Christmas Island lava series would eliminate the majority of the data set (Figure 12). Although suites with low Os and high 187 Os/ 188 Os values are clearly related to crustal contamination [93], applying a filter would also eliminate a significant number of data sets at low Os ppt which have been demonstrated to not have suffered crustal contamination or seawater alteration [74,80,83,94]. An alternative to applying a filter is to look for correlations between Os isotopic values and other geochemical indicators of crustal contamination.…”