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Long-term storage of subduction-related volatiles in Northern Victoria Land lithospheric mantle: Insight from olivine-hosted melt inclusions from McMurdo basic lavas (Antarctica)
Lithos ( IF 3.5 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.lithos.2020.105826
P.P. Giacomoni , C. Bonadiman , F. Casetta , B. Faccini , C. Ferlito , L. Ottolini , A. Zanetti , M. Coltorti

Abstract H2O, CO2, F, Cl and S concentrations in olivine-hosted melt inclusions (MI) from Cenozoic alkaline volcanics of Northern Victoria Land (NVL, Antarctica) were determined by Secondary Ion Mass Spectrometry (SIMS). The most undegassed H2O and CO2 values varies from 1.14 to 2.64 wt% H2O and from 2320 to 3900 ppm CO2 for the least differentiated alkaline basalts and basanites, respectively. The same MI have F and Cl contents varying from 471 to 888 and from 474 to 1135 respectively, although some other MI can get up to 1377 of F and 1336 of Cl. A H2O/(H2O + CO2) molar ratios from 0.88 to 0.92 were determined, and taking into account the MI with the highest water content, a CO2 content in the melts up to 4400 and 8800 ppm for basaltic and basanitic compositions were inferred. Assuming that these magmas were produced by about 3 to 7% of partial melting, the volatile content in the mantle sources were estimated and compared with the estimates obtained from amphibole-bearing mantle xenoliths abundantly entrained in the McMurdo basic lavas. The two approaches converge in obtaining the following values: H2O = 1160 ± 436 ppm; CO2 = 304 ± 64 ppm. Some discrepancies are observed for F and Cl, mainly due to the uncertainties in the F and Cl contents of amphibole and its modal content, both parameters spanning a rather large range. The resulting CO2/Nb and CO2/Ba ratios are lower and H2O/Ce higher than those estimated for Depleted MORB Mantle (DMM), suggesting that the NVL Cenozoic alkaline magmatism could be originated by an enriched mantle source composed by 60 to 70% Enriched Mantle (EM) and from 40 to 30% DMM. A global comparison of fluid-related, highly incompatible and immobile/low incompatible elements such as Li, K, Cl, Ba, Nb, Dy and Yb allow to put forward that the prolonged (~500 to 100 Ma) Ross subduction event played a fundamental role in providing the volatile budget to the lithospheric mantle before the onset of the Cenozoic continental rifting.

中文翻译:

维多利亚州北部岩石圈地幔中俯冲相关挥发物的长期储存:从麦克默多基性熔岩(南极洲)的橄榄石熔体包裹体洞察

摘要 通过二次离子质谱法 (SIMS) 测定了来自维多利亚州北部地区(NVL,南极洲)新生代碱性火山岩的橄榄石熔体包裹体 (MI) 中的 H2O、CO2、F、Cl 和 S 浓度。对于差异最小的碱性玄武岩和玄武岩,大多数未脱气的 H2O 和 CO2 值分别为 1.14 至 2.64 wt% H2O 和 2320 至 3900 ppm CO2。相同的 MI 的 F 和 Cl 含量分别从 471 到 888 和从 474 到 1135 不等,尽管其他一些 MI 可以得到高达 1377 的 F 和 1336 的 Cl。确定了 0.88 至 0.92 的 H2O/(H2O + CO2) 摩尔比,并考虑到具有最高水含量的 MI,推断玄武岩和玄武岩组合物熔体中的 CO2 含量高达 4400 和 8800 ppm。假设这些岩浆是由大约 3% 到 7% 的部分熔融产生的,估计地幔源中的挥发分含量,并与从麦克默多基性熔岩中大量夹带的含闪石的地幔包体中获得的估计值进行比较。这两种方法在获得以下值时趋同:H2O = 1160 ± 436 ppm;CO2 = 304 ± 64 ppm。观察到 F 和 Cl 的一些差异,主要是由于闪石的 F 和 Cl 含量及其模态含量的不确定性,这两个参数跨越了相当大的范围。由此产生的 CO2/Nb 和 CO2/Ba 比值低于枯竭 MORB 地幔 (DMM) 的估计值,而 H2O/Ce 比估计值更高,表明 NVL 新生代碱性岩浆作用可能起源于由 60% 至 70%地幔 (EM) 和 40% 到 30% 的 DMM。
更新日期:2020-12-01
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