Journal of Petrology | Volume 45 | Number 1 | Pages 107-138 | 2004
© Oxford University Press 2004; all rights reserved
Petrology and Geochemistry of Early Cretaceous Bimodal Continental Flood Volcanism of the NW Etendeka, Namibia. Part 2: Characteristics and Petrogenesis of the High-Ti Latite and High-Ti and Low-Ti Voluminous Quartz Latite Eruptives
1 ADVANCED CENTER FOR QUEENSLAND UNIVERSITY ISOTOPE RESEARCH EXCELLENCE (ACQUIRE), THE UNIVERSITY OF QUEENSLAND, ST. LUCIA, QLD. 4072, AUSTRALIA
2 DEPARTMENT OF GEOLOGY, RHODES UNIVERSITY, GRAHAMSTOWN 6140, SOUTH AFRICA
3 PANALYTICAL, LELYWEG 1, 7602EA ALMELO, THE NETHERLANDS
4 DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF CAPE TOWN, RONDEBOSCH 7700, SOUTH AFRICA
5 RESEARCH SCHOOL OF EARTH SCIENCES, THE AUSTRALIAN NATIONAL UNIVERSITY, CANBERRA, A.C.T. 0200, AUSTRALIA
* Corresponding author. E-mail: ewart{at}cust.caloundra.net
As a result of their relative concentration towards the respective Atlantic margins, the silicic eruptives of the Paraná (Brazil)–Etendeka large igneous province are disproportionately abundant in the Etendeka of Namibia. The NW Etendeka silicic units, dated at 
132 Ma, occupy the upper stratigraphic levels of the volcanic sequences, restricted to the coastal zone, and comprise three latites and five quartz latites (QL). The large-volume Fria QL is the only low-Ti type. Its trace element and isotopic signatures indicate massive crustal input. The remaining NW Etendeka silicic units are enigmatic high-Ti types, geochemically different from low-Ti types. They exhibit chemical affinities with the temporally overlapping Khumib high-Ti basalt (see Ewart et al. Part 1) and high crystallization temperatures (
980 to 1120°C) inferred from augite and pigeonite phenocrysts, both consistent with their evolution from a mafic source. Geochemically, the high-Ti units define three groups, thought genetically related. We test whether these represent independent liquid lines of descent from a common high-Ti mafic parent. Although the recognition of latites reduces the apparent silica gap, difficulty is encountered in fractional crystallization models by the large volumes of two QL units. Numerical modelling does, however, support large-scale open-system fractional crystallization, assimilation of silicic to basaltic materials, and magma mixing, but cannot entirely exclude partial melting processes within the temporally active extensional environment. The fractional crystallization and mixing signatures add to the complexity of these enigmatic and controversial silicic magmas. The existence, however, of temporally and spatially overlapping high-Ti basalts is, in our view, not coincidental and the high-Ti character of the silicic magmas ultimately reflects a mantle signature.
KEY WORDS: large-volume quartz latites; magma mixing; open-system fractional crystallization; crustal assimilation; high-Ti and low-Ti provinciality
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  R. N. Thompson, A. J. V. Riches, P. M. Antoshechkina, D. G. Pearson, G. M. Nowell, C. J. Ottley, A. P. Dickin, V. L. Hards, A.-K. Nguno, and V. Niku-Paavola Origin of CFB Magmatism: Multi-tiered Intracrustal Picrite-Rhyolite Magmatic Plumbing at Spitzkoppe, Western Namibia, during Early Cretaceous Etendeka Magmatism J. Petrology, June 1, 2007; 48(6): 1119 - 1154. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Miller and C. Harris Petrogenesis of the Swaziland and Northern Natal Rhyolites of the Lebombo Rifted Volcanic Margin, South East Africa J. Petrology, January 1, 2007; 48(1): 185 - 218. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. BOGAERTS, B. SCAILLET, and J. V. AUWERA Phase Equilibria of the Lyngdal Granodiorite (Norway): Implications for the Origin of Metaluminous Ferroan Granitoids J. Petrology, December 1, 2006; 47(12): 2405 - 2431. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. SCAILLET and R. MACDONALD Experimental and Thermodynamic Constraints on the Sulphur Yield of Peralkaline and Metaluminous Silicic Flood Eruptions J. Petrology, July 1, 2006; 47(7): 1413 - 1437. [Abstract] [Full Text] [PDF]
|
|