Depletion Events, Nature of Metasomatizing Agent and Timing of Enrichment Processes in Lithospheric Mantle Xenoliths from the Veneto Volcanic Province   总被引：1，自引：1，他引：1  

BECCALUVA  L.; BONADIMAN  C.; COLTORTI  M.; SALVINI  L.; SIENA  F. 《Journal of Petrology》2001,42(1):173-188

Mantle xenoliths included in the alkaline basic lavas from thePaleogene Veneto Volcanic Province (VVP) consist of predominantspinel lherzolites (21–6% clinopyroxene) and minor spinelharzburgites (4–2% clinopyroxene), mainly protogranulartextured. Most of the xenoliths show superimposed textural evidenceof metasomatic processes, consisting of reaction patches andspongy clinopyroxenes, variably associated with glass and secondaryolivine, clinopyroxene, spinel and feldspar. Whole-rock andmineral major and trace element data indicate a complex historyof depletion and enrichment processes undergone by the continentallithospheric mantle beneath a within-plate region. Protogranular-texturedclinopyroxenes from lherzolites show heavy rare earth element(HREE) contents  相似文献   

Kimberlite-like Metasomatism and 'Garnet Signature' in Spinel-peridotite Xenoliths from Sal, Cape Verde Archipelago: Relics of a Subcontinental Mantle Domain within the Atlantic Oceanic Lithosphere?   总被引：2，自引：0，他引：2  

BONADIMAN  C.; BECCALUVA  L.; COLTORTI  M.; SIENA  F. 《Journal of Petrology》2005,46(12):2465-2493

A mantle xenolith suite from two Late Tertiary necks on SalIsland (Cape Verde Archipelago) consists of nearly equivalentamounts of anhydrous spinel-bearing lherzolites and harzburgites,in which secondary metasomatic textural domains are superimposedon the original protogranular textures. Detailed petrographicstudies, coupled with in situ major and trace element analysesof the constituent minerals and interstitial glasses, revealthe complex evolutionary history of the Cape Verde lithosphericmantle, from depletion in the garnet facies to re-equilibrationand re-enrichment in the spinel stability field. Low CaO (16·4–18·0wt %) and heavy rare earth element (HREE; Yb_n = 2·4–4·8),and high Cr₂O₃ (1·06–1·84 wt %) contentsin the clinopyroxenes of the lherzolites can be quantitativelyaccounted for by (1) low-degree (4%) partial melting of a PrimitiveMantle-like garnet lherzolite followed by (2) partial re-equilibrationof the melting residuum from the garnet to the spinel stabilityfield. This model is further supported by thermobarometric estimates(T = 975–1210°C; P = 1·3–2·1 GPa),which cluster around the spinel–garnet boundary in theperidotite system. Secondary parageneses, regardless of theprimary lithologies, are characterized by (1) two clinopyroxenes,cpx2-O and cpx2-C, respectively related to orthopyroxene andclinopyroxene destabilization after reaction with metasomaticfluids, and (2) glasses with anomalously high, even for continentalsettings, K₂O contents (up to 8·78 wt %), together withK-feldspar. Major and trace element mass balance calculationsbetween the primary and secondary parageneses suggest infiltrationof a kimberlite-like metasomatizing agent (on volatile-freebasis, MgO 17–27 wt %; K₂O/Na₂O 1·6–3·2molar; (K₂O + Na₂O)/Al₂O₃ 1·1–3·0 molar;Rb 91–165 ppm; Zr 194–238 ppm). The kimberlite-likemetasomatism in the Cape Verde lithospheric mantle, togetherwith the presence of lherzolitic domains, partially re-equilibratedfrom the garnet to the spinel stability field, may suggest thepresence of subcontinental mantle lithosphere relicts left behindby drifting of the African Plate during the opening of the CentralAtlantic Ocean. KEY WORDS: Cape Verde; mantle metasomatism; garnet signatures; clinopyroxenes; kimberlites  相似文献