Author Instructions for Abstract Submission to the CIGCM 2016

Author instructions for abstract submission to the CIGCM 2016

Abstracts on two pages maximum should be sent by 15 October 2016 following the requirements below :

Title (Arial, 14 pts, bold, centered, capitalize only first word and proper nouns).

Author (s) : (Arial, 11 pt, normal, capitalize the initial, centered).

Institution (s) : (Arial, 10 pt, italic, centered).

Use numbers in superscript for relate authors to their affiliation.

Abstract text : (Arial, 11 pt, normal, left and right justified).

Keywords : Insert at the end of the text. Maximum 5 keywords.

References: (Arial, 10 pt, italic, must include the author name, year of publication and bibliographic source).

Abstracts may contain figures inserted at the following format: JPG, GIF or PNG.

Abstract should be sent to the following email addresses by 15 october 2016 :

A sample abstract is given below.

Petrography, mineralogy and geochemistry of lamproitic rocks of Kef Hahouner (North-East Algeria)

Mohamed Yacine Laghouag1, Moulley Charaf Chabou1, Gaston Godard2

1Département des Sciences de la Terre, Institut d’Architecture et des Sciences de la Terre, Université Ferhat Abbas, Sétif. . 2Institut de physique du Globe, Sorbonne Paris Cite, Université Paris-Diderot, UMR 7154 CNRS, 1, rue Jussieu, 75238 Paris cedex 05, France.

Lamproites are rare ultrapotassic rocks of economic importance because they may be hostrocks of diamonds. Small outcrops of lamproitic rocks have been reported in Northeastern Algeria, near Kef Hahouner and Koudiat el Anzazza (Raoult and Velde, 1971; Vila et al., 1974), but only few studies have been done on these rocks. We have conducted petrographic, mineralogical and geochemical study on the volcanic massif of Kef Hahouner. The rocks of the massif occurs as lava flows within the continental Miocene of the Constantine basin. Our study indicates the existence of two types of rocks: lamproitic rocks at the bottom and shoshonites at the top, which are separated by a red level of continental Miocene. Lamproitic rocks are composed of (fig. 1) olivine phenocrysts (Fo72-87) in a groundmass composed of sanidine with a barium-rich core, clinopyroxene (Wo43En46Fs11), plagioclase (labrador, An50-65), apatite, phlogopite and glass. Opaque minerals consist of titaniferous and chromiferous spinels often included in olivine. chlorophaite and bowlingite are the main alteration minerals..

Figure 1. Example of a SEM image processed by ACP 123 of an area of KH1 thin section (lamproitic rock) showing the main mineral phases.

Geochemically, the lamproitic rocks are ultrapotassic (K2O/Na2O > 2 ; K2O > 3% and MgO > 3) with a high [Mg] ([Mg] = Mg/(Mg+Fe2+)) around 0,71, indicating that the studied rocks are relatively primitive in character. The chondrite-normalized rare-earth element (REE) patterns of the lamproitic rocks display a high LREE enrichment relative to HREE and the primitive mantle-normalized multi-trace element patterns show an extreme enrichment in large ion lithophile elements (LILE) such as Cs, Ba, Rb, Th, U and LREE with concentrations of about 3000 times higher than primitive mantle (fig. 2). Shoshonites are composed of plagioclases laths (Labrador, An60-70) in a groundmass composed of barium-rich sanidine, clinopyroxene (Wo45En42Fs14), apatite and ilmenite. Large crystals of calcite occupy the rock vesicles or replace ferromagnesian minerals, probably olivine. Shoshonites show a chondrite-normalized rare-earth element (REE) and primitive mantle-normalized multi-trace element patterns similar to those of the lamproitic rocks, but with less important LREE and LILE contents (fig. 2).

Figure 2. Chondrite-normalized rare-earth element (REE) (left) and primitive mantle-normalized multi-trace element patterns (right) of the Kef Hahouner volcanic rocks (in red: lamproitic rocks; in blue : shoshonite).

The rare-earth element (REE) and multi-trace element patterns of Kef Hahouner lamproitic rocks are similar to those of lamproites of the Mediterranean basin, which indicates same petrographic affinity and a common origin. A south vergence subduction followed by a post-collisional lithosphere delamination may be responsible of the lamproitic and shoshonitic volcanism in this part of the Maghrebides chain.

Keywords : Lamproites – Shoshonites – Kef Hahouner – Petrography - Geochemistry.

References

Raoult, J.-F., Velde, D., 1971. Comptes Rendus de l’Académie des Sciences Paris, Série D 272, 1051–1054.

Vila, J.-M., Hernandez, J., Velde, D., 1974. Comptes Rendus de l’Académie des Sciences Paris, Série D 278, 2589–2592.