The Early Cenozoic alkaline complex of Morro de Sa˜o Joa˜o intrudes the Precambrian basement at the eastern end of the Rio de Janeiro coastline. It is mostly made up of melanocratic nepheline syenites and nepheline syenites, with subordinate clinopyroxenites, shonkinites (melasyenites), and alkali gabbros. Melanocratic nepheline syenites and nepheline syenites are cross-cut by thin dykes, ranging in composition from phonotephrite to phonolite. The mafic–ultramafic rocks are meso- to orthocumulates, with mineral compositions and whole-rock chemistry suggesting crystallization from a moderately evolved batch of magmas (potassic tephrite/phonotephrite). Melanocratic nepheline syenites and nepheline syenites likely represent magma–crystal mixtures, whereas a few finegrained rocks roughly approximate liquid compositions; alkali syenites are typical cumulitic rocks. Major and trace element compositions reflect a genesis of clinopyroxenitic to shonkinitic rocks from tephritic parental magmas, which evolved toward phonotephritic and phonolitic compositions. Initial 87Sr/86Sr and 143Nd/144Nd ratios (0.7048–0.7061 and 0.51231–0.51239, respectively) overlap the values in the analog intrusions of the Serra do Mar province, supporting a genesis from similar parental magmas and source mantle. The dominant lithospheric components of the latter may be responsible for the potassic affinity and strongly incompatible element enrichment of the derived melts.

PETROGENESIS OF THE EARLY CENOZOIC POTASSIC ALKALINE COMPLES OF MORRO SAO JOAO, SOUTHEASTERN BRAZIL / Brotzu, P.; Melluso, L.; Bennio, L.; Gomes, C. B.; Lustrino, Michele; Morbidelli, L.; Morra, V.; Ruberti, E.; Tassinari, C.; D'Antonio, M.. - In: JOURNAL OF SOUTH AMERICAN EARTH SCIENCES. - ISSN 0895-9811. - STAMPA. - 24:(2007), pp. 93-115. [10.1016/j.jsames.2007.02.006]

PETROGENESIS OF THE EARLY CENOZOIC POTASSIC ALKALINE COMPLES OF MORRO SAO JOAO, SOUTHEASTERN BRAZIL

LUSTRINO, Michele;
2007

Abstract

The Early Cenozoic alkaline complex of Morro de Sa˜o Joa˜o intrudes the Precambrian basement at the eastern end of the Rio de Janeiro coastline. It is mostly made up of melanocratic nepheline syenites and nepheline syenites, with subordinate clinopyroxenites, shonkinites (melasyenites), and alkali gabbros. Melanocratic nepheline syenites and nepheline syenites are cross-cut by thin dykes, ranging in composition from phonotephrite to phonolite. The mafic–ultramafic rocks are meso- to orthocumulates, with mineral compositions and whole-rock chemistry suggesting crystallization from a moderately evolved batch of magmas (potassic tephrite/phonotephrite). Melanocratic nepheline syenites and nepheline syenites likely represent magma–crystal mixtures, whereas a few finegrained rocks roughly approximate liquid compositions; alkali syenites are typical cumulitic rocks. Major and trace element compositions reflect a genesis of clinopyroxenitic to shonkinitic rocks from tephritic parental magmas, which evolved toward phonotephritic and phonolitic compositions. Initial 87Sr/86Sr and 143Nd/144Nd ratios (0.7048–0.7061 and 0.51231–0.51239, respectively) overlap the values in the analog intrusions of the Serra do Mar province, supporting a genesis from similar parental magmas and source mantle. The dominant lithospheric components of the latter may be responsible for the potassic affinity and strongly incompatible element enrichment of the derived melts.
2007
Shonkinites; Nepheline syenites; Morro de Sao Joao intrusive Complex; Southeastern Brazil
01 Pubblicazione su rivista::01a Articolo in rivista
PETROGENESIS OF THE EARLY CENOZOIC POTASSIC ALKALINE COMPLES OF MORRO SAO JOAO, SOUTHEASTERN BRAZIL / Brotzu, P.; Melluso, L.; Bennio, L.; Gomes, C. B.; Lustrino, Michele; Morbidelli, L.; Morra, V.; Ruberti, E.; Tassinari, C.; D'Antonio, M.. - In: JOURNAL OF SOUTH AMERICAN EARTH SCIENCES. - ISSN 0895-9811. - STAMPA. - 24:(2007), pp. 93-115. [10.1016/j.jsames.2007.02.006]
File allegati a questo prodotto
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/39257
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 52
  • ???jsp.display-item.citation.isi??? 38
social impact