Geochemical data are presented for the meta-igneous, mafic-ultramafic complex near Finero. This complex is in contact with a phlogopite-bearing mantle peridotite and is subdivided into the Internal Gabbro unit, the Amphibole Peridotite unit, and the External Gabbro unit. The Internal Gabbro and the Amphibole Peridotite units consist of coarse-grained, chemically heterogeneous cumulates, whereas the External Gabbro unit is generally massive, chemically more uniform and approximately representative of the residual melt with MgO contents between 6.6 and 9.1% and Mg numbers between 38 and 58. Both whole-rock and mineral contents of Ni and Cr are significantly higher (at similar Mg numbers) in the Amphibole Peridotite unit than in the Internal Gabbro, unit. The most straightforward interpretation of this is that the Amphibole Peridotite unit accumulated after the influx of fresh mafic (or ultramafic) magma into the magma chamber. Major-element chemical trends are continuous from the Amphibole Peridotite unit to the External Gabbro unit and are consistent with closed-system fractionation with no further addition of magma or contamination by wall or roof rock assimilation. In the External Gabbro unit, total FeO and TiO2 contents are strongly correlated with each other (and with P2O5 and Zr) and reach values as high as 19 and 4%, respectively, indicating an advanced degree of crystal fractionation along a tholeiitic trend. The External Gabbro samples have generally smooth normalized trace element patterns, which are consistent with being representative of a liquid composition. The residual nature of the External Gabbro magma is also indicated by negative Eu and Sr anomalies, clear evidence for prior feldspar-fractionation. REE patterns are otherwise indistinguishable from N-type MORE, but Th and U an significantly more depleted than in MORE. This Th and U depletion is similar to that found in olivine basalts and picrites on Iceland and Hawaii; its origin is not well understood. No evidence is seen for any assimilation of crustal material, in sharp contrast with the situation of the igneous complex in Val Sesia near Balmuccia, where the magma composition is dominated by assimilation of crust. We suggest that the heat provided by at most two injections of magma near Finero was insufficient to induce crustal anatexis, in contrast with the excess heat supplied by multiple magma injections at Balmuccia.

The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone) .1. Chemistry of MORB-like magmas / Mh, Lu; Aw, Hofmann; Mazzucchelli, Maurizio; Rivalenti, Giorgio. - In: CHEMICAL GEOLOGY. - ISSN 0009-2541. - STAMPA. - 140(1997), pp. 207-222.

The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone) .1. Chemistry of MORB-like magmas

MAZZUCCHELLI, Maurizio;RIVALENTI, Giorgio
1997

Abstract

Geochemical data are presented for the meta-igneous, mafic-ultramafic complex near Finero. This complex is in contact with a phlogopite-bearing mantle peridotite and is subdivided into the Internal Gabbro unit, the Amphibole Peridotite unit, and the External Gabbro unit. The Internal Gabbro and the Amphibole Peridotite units consist of coarse-grained, chemically heterogeneous cumulates, whereas the External Gabbro unit is generally massive, chemically more uniform and approximately representative of the residual melt with MgO contents between 6.6 and 9.1% and Mg numbers between 38 and 58. Both whole-rock and mineral contents of Ni and Cr are significantly higher (at similar Mg numbers) in the Amphibole Peridotite unit than in the Internal Gabbro, unit. The most straightforward interpretation of this is that the Amphibole Peridotite unit accumulated after the influx of fresh mafic (or ultramafic) magma into the magma chamber. Major-element chemical trends are continuous from the Amphibole Peridotite unit to the External Gabbro unit and are consistent with closed-system fractionation with no further addition of magma or contamination by wall or roof rock assimilation. In the External Gabbro unit, total FeO and TiO2 contents are strongly correlated with each other (and with P2O5 and Zr) and reach values as high as 19 and 4%, respectively, indicating an advanced degree of crystal fractionation along a tholeiitic trend. The External Gabbro samples have generally smooth normalized trace element patterns, which are consistent with being representative of a liquid composition. The residual nature of the External Gabbro magma is also indicated by negative Eu and Sr anomalies, clear evidence for prior feldspar-fractionation. REE patterns are otherwise indistinguishable from N-type MORE, but Th and U an significantly more depleted than in MORE. This Th and U depletion is similar to that found in olivine basalts and picrites on Iceland and Hawaii; its origin is not well understood. No evidence is seen for any assimilation of crustal material, in sharp contrast with the situation of the igneous complex in Val Sesia near Balmuccia, where the magma composition is dominated by assimilation of crust. We suggest that the heat provided by at most two injections of magma near Finero was insufficient to induce crustal anatexis, in contrast with the excess heat supplied by multiple magma injections at Balmuccia.
140
207
222
The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone) .1. Chemistry of MORB-like magmas / Mh, Lu; Aw, Hofmann; Mazzucchelli, Maurizio; Rivalenti, Giorgio. - In: CHEMICAL GEOLOGY. - ISSN 0009-2541. - STAMPA. - 140(1997), pp. 207-222.
Mh, Lu; Aw, Hofmann; Mazzucchelli, Maurizio; Rivalenti, Giorgio
File in questo prodotto:
File Dimensione Formato  
1997_1LuEtAlBIS.PDF

non disponibili

Tipologia: Post-print dell'autore (bozza post referaggio)
Dimensione 877.7 kB
Formato Adobe PDF
877.7 kB Adobe PDF   Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

Caricamento pubblicazioni consigliate

Licenza Creative Commons
I metadati presenti in IRIS UNIMORE sono rilasciati con licenza Creative Commons CC0 1.0 Universal, mentre i file delle pubblicazioni sono rilasciati con licenza Attribuzione 4.0 Internazionale (CC BY 4.0), salvo diversa indicazione.
In caso di violazione di copyright, contattare Supporto Iris

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11380/306809
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 30
  • ???jsp.display-item.citation.isi??? 31
social impact