Download InstrAbstr

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 :
[email protected]
[email protected]
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. [email protected]. 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 mantlenormalized 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 postcollisional 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.