IJG  Vol.6 No.1 , January 2015
Geochemistry and Petrology of Basic Volcanic Rocks of Jabal Al Haruj Al-Aswad, Libya
ABSTRACT
The Al Haruj Intra-continental Volcanic Province is the largest part of the extensive volcanic activity in Libya which is considered to be a typical within plate basalts. The volcano-tectonics evolution of this province, as well as its origin, are still widely disputed. According to K-Ar dating previously studied, the volcanic activity started in the Late Miocene and lasted until at least the Late Pleistocene. The field may still be volcanically active. The mafic rocks of Jabal Al Haruj have been classified into six major phases or groups. These phases have been differentiated using Landsat images together with aerial photographs of different scales as well as field observations. The topographic forms of the earliest phase are highly eroded while the forms of the latest phase are usually fresh and very well preserved as regards primary features. Mafic lavas of this field consist of alkali basalts to olivine tholeiites (transitional basalt) which contain olivine as essential constituent together with clinopyroxene, plagioclase and glass. The basalt exhibits intergranular, intersertal, ophitic and subophitic relations. Amygdaloidal and glomerporphyritic textures are also observed. The basaltic rocks of different ages and from different localities are petrographically rather similar. Phenocrysts of olivine probably the result from slow cooling in crustal magma chambers prior to eruptions, suggesting that magmas ascended slowly through the crust. 109 samples have been carefully collected from various phases, some of these samples have been chosen for major and trace elements analyses, using XRF in order to determine the characteristics of the mantle source and investigate crustal interaction. The major and trace elements revealed a slightly significant chemical diversity among the phases and within each phase. The normative classification of most of these rocks shows close agreement with their modal classification. A vague correlation between MgO and most major oxides in the studied samples suggests different degrees of partial melting rather than fractional crystallization. A characteristic feature of the studied volcanic rocks is the relatively constant ratios of certain incompatible trace elements (Nb/Zr, Rb/Zr), which provides strong evidence of a common source. In addition, the rocks display similar patterns of the peaks and troughs; this strongly suggests that they have a common parent and common subsequent processes. The compatible transitional metals Ni (81 - 193 ppm) and Cr contents (238 - 361 ppm) and relatively low Mg# (Mg/(Mg + Fet)) (52 - 62) give an indication that the studied basaltic rocks have slightly to moderately fractionated olivine and/or spinel. The magmatism of this volcanic field seems to be related to reactivation of pre-existing structures during the passive rifting of the Sirt Basin that most likely produced in response to convergence between European and African plates since Jurassic until Holocene times.

Cite this paper
Al-Hafdh, N. and El-Shaafi, A. (2015) Geochemistry and Petrology of Basic Volcanic Rocks of Jabal Al Haruj Al-Aswad, Libya. International Journal of Geosciences, 6, 109-144. doi: 10.4236/ijg.2015.61008.
References
[1]   Busrewil, M.T. and Wadsworth, W.J. (1980) Preliminary Chemical Data on the Volcanic Rocks of Al Haruj Area, Central Libya. In: Salem, M.J. and Busrewil, M.T., Eds., The Geology of Libya, Vol. 3, Academic Press, London, 1077-1080.

[2]   Busrewil, M.T. and Suwesi, S.Kh. (1993) Geological Map of Libya 1:250,000, Sheet. Al Haruj Al Aswad NG 33-4. Explanatory Booklet. Industrial Research Centre, Tripoli, 95.

[3]   Nemeth, K., Suwesi, Kh., Peregi, Z., Gulacsi, Z. and Ujszaszi, J. (2003) Plio/Pleistocene Flood Basalt Related Scoria and Spatter Cones, Rootless Lava Flows and Pit Craters, Al Haruj Al Abiyad, Libya. Geolines, 15, 107-112.

[4]   Busrewil, M.T. and Wadsworth, W.J. (1996) Tertiary-Quaternary Alkaline Subalkaline Magmatism in Gharayan Area: Field Aspects and Petrography. PRJ, 8, 13-23.

[5]   Peregi, Zs., Less, G.Y., Konrad, Gy., Fodor, L., Gulacsi, Z., Gyalog, L., Turki, S.M., Suwesi, S.Kh., Sherif, Kh. and Dalub, H. (2003) Explanatory Booklet. Geological Map of Libya 1:250,000. Sheet: Al Haruj Al Abyad NG 33-8. Industrial Research Centre, Tripoli, 248.

[6]   El-Shaafi Abd El-Salam, S. (2008) Geochemistry and Petrology of Basic Volcanic Rocks of the NE. Part of Jabal AL-Haruj AL-Aswad, Central Libya. Unpublished MSc Thesis, University of Benghazi, Libya.

[7]   Hallett, D. (2002) Petroleum Geology of Libya. Elsevier, Amsterdam.

[8]   Klitzsch, E. (2000) The Structural Development of the Murzuq and Kufra Basins: Significance for Oil and Mineral Exploration. In: Sola, M.A. and Worsley, D., Eds., Geological Exploration of the Murzuq Basin, Elsevier, Amsterdam, 143-150. http://dx.doi.org/10.1016/B978-044450611-5/50009-X

[9]   Woller, F. and Fediuk, F. (1980) Volcanic Rocks of Gabal as Sawda. In: Salem, M.J. and Busrewil, M.T., Eds., The Geology of Libya, Vol. 3, Academic Press, London, 1081-1093.

[10]   Pesce, A. (1966) Uau en Nammus: South Central Libya and Northern Chad. Excursions f?hrer der petroleum Exploration Society of Libya, Tripoli, 47-51.

[11]   Ade Hall, F.M., Reynolds, P.H., Dagley, P., Musset, A.G., Hubbard, T.B. and Klitzsch, E. (1974) Geophysical Studies of North African Cenozoic Volcanic Areas Al Haruj Al-Assuad, Libya. Canadian Journal of Earth Science, 11, 998-1006. http://dx.doi.org/10.1139/e74-096

[12]   Less, Gy., Turki, S.M., Suwesi, S.Kh., Peregi, L.F., Koloszar, L., Kalmar, J., Sherif, Kh., Csaszar, G., Gulasci, Z., Dalum, H. and Al Tajuri, A. (2006) Explanatory Booklet. Geological Map of Libya 1:250,000. Sheet: Waw Al Kabir NG 33-12. Industrial Research Centre, Tripoli, 295.

[13]   Klitzsch, E. (1968) Der Basalt Vulkanismus des Djebel Haroudj, Ostfezzan, Libya. Geologische Rundschau, 57, 585-609. http://dx.doi.org/10.1007/BF01821263

[14]   Farahat, E.S., Abdel Ghani, M.S., Aboazom, A.S. and Asran, A.M.H. (2006) Mineral Chemistry of Al Haruj LowVolcanicity Rift Basalts, Libya: Implications for Petrogenetic and Geotectonic Evolution. Journal of African Earth Sciences, 45, 198-212. http://dx.doi.org/10.1016/j.jafrearsci.2006.02.007

[15]   Vesely, J. (1985) Geological Map of Libya 1:250,000 Sheet: Zallah NH 33-16. Explanatory Booklet. Industrial Research Centre, Tripoli, 125.

[16]   Woller, F. (1984) Geological Map of Libya 1:250,000, Sheet: Al Fuquaha NG 33-3. Explanatory Booklet. Industrial Research Centre, Tripoli, 123.

[17]   Mackenzie, W.S. and Adams, A.E. (1995) A Color Atlas of Rocks and Minerals in Thin Section. Manson, London.

[18]   Hatch, F.H., Wells, A.K. and Wells, M.K. (1972) Petrology of the Igneous Rocks, Fifth Impression. Thomas Murby, London.

[19]   Cox, K.G., Bell, J.D. and Pankhurst, R.J. (1979) The Interpretation of Igneous Rocks. Allen & Unwin, London. http://dx.doi.org/10.1007/978-94-017-3373-1

[20]   Middlemost, E.A.K. (1980) Iron Oxidation Ratios, Norms and the Classification of Volcanic Rocks. Chemical Geology, 77, 19-26.

[21]   Middlemost, E.A.K. (1975) The Basalt Clan. Earth Science Reviews, 11, 337-364.
http://dx.doi.org/10.1016/0012-8252(75)90039-2

[22]   Winter, J.W. (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

[23]   Winchester, J.A. and Floyd, P.A. (1976) Geochemical Discrimination of Different Magma Series and Their Differentiation Products Using Immobile Elements. Chemical Geology, 20, 325-343.
http://dx.doi.org/10.1016/0009-2541(77)90057-2

[24]   Rollinson, H.R. (1993) Using Geochemical Data, Evolution, Presentation, Interpretation. Longman Scientific & Technical, Oxford/John Wiley, New York, 1-206.

[25]   Yoder, H.S. and Tilley, C.E. (1962) Origin of Basalt Magmas: An Experimental Study of Natural and Synthetic Rock Systems. Journal of Petrology, 3, 342-532.
http://dx.doi.org/10.1093/petrology/3.3.342

[26]   Thompson, R.N. (1984) Dispatches from the Basalts Front. 1. Experiments. Proceedings of the Geologists’ Association, 95, 249-262. http://dx.doi.org/10.1016/S0016-7878(84)80011-5

[27]   Wilkinson, J.F.G. (1986) Classification and Average Chemical Composition of Common Basalts and Andesites. Journal of Petrology, 27, 181-194. http://dx.doi.org/10.1093/petrology/27.1.31

[28]   Busrewil, M.T. and Oun, K.M. (1991) Geochemistry of the Tertiary Alkaline Rocks of Jabal al Hasawnah, West Libya. In: Salem, M.J., Busrewil, M.T. and Ben Ashour, A.M., Eds., Geology of Libya, Vol. 7, Elsevier, Amsterdam, 2587-2598.

[29]   Baker, B.H. (1987) Outline of the Petrology of the Kenya Rift Alkaline Province. In: Fitton, J.G. and Upton, B.J., Eds., Alkaline Igneous Rocks, Geological Society, Special Publications, London, 293-311.

[30]   Pearce, J.A. (1983) Lithosphere in Magma Genesis at Active Continental Margins. In: Hawesworth, C.J. and Norry, M.J., Eds., Continental Basalts and Mantle Xenoliths, Shiva.

[31]   Aboazom, A.S. (2005) Petrogenesis of Phase 6 of Al Haruj Al Aswad Volcanic Province, Central Libya. Sebha University Journal, 4, 96-113.

[32]   Fitton, J.G., James, D., Kempton, P.D., Ormerod, D.S. and Leeman, W.P. (1988) The Role of the Lithospheric Mantle in the Generation of Late Cenozoic Basic Magmas in the Western United States. J. Petrol. Special Lithosphere Issue, 331-349.

[33]   Hawkesworth, C.J., Hempton, P.D., Ellam, R.M. and Calsteren, P. (1990) Continental Mantle Lithosphere and Shallow Level Enrichment Processes in the Earth’s Mantle. Earth and Planetary Science Letters, 96, 256-268. http://dx.doi.org/10.1016/0012-821X(90)90006-J

[34]   Hopper, P.R., Bailey, D.G. and Hawkeworth, C.J. (1993) Isotopic and Geochemical Constraints on the Origin and Evolution of the Columbia River Basalt. Journal of Petrology, 34, 1203-1246.
http://dx.doi.org/10.1093/petrology/34.6.1203

[35]   Longmuir, C.H., Beneder, J.F., Bence, A.E., Hanson, G.N. and Taylor, S.R. (1977) Petrogenesis of Basalts from the Famous Area: Mid-Oceanic Ridge. Earth and Planetary Science Letters, 36, 133-156. http://dx.doi.org/10.1016/0012-821X(77)90194-7

[36]   Kay, R.W. and Hubbard, N.J. (1978) Trace Elements in Ocean Ridge Basalts. Earth and Planetary Science Letters, 38, 95-116. http://dx.doi.org/10.1016/0012-821X(78)90128-0

[37]   Sun, S.S. (1980) Lead Isotopic Study Volcanic Rocks from Mid-Ocean Ridges, Ocean Islands and Islands Arcs. Philosophical Transactions of the Royal Society A, 297, 409-445.
http://dx.doi.org/10.1098/rsta.1980.0224

[38]   Pearce, J.A. (1976) Statistical Analysis of Major Element Patterns in Basalts. Journal of Petrology, 17, 15-43. http://dx.doi.org/10.1093/petrology/17.1.15

[39]   Pearce, J.A. (1980) Geochemical Evidence for the Genesis and Eruptive Settings of Lavas from Tethyan Ophiolites. Proceedings of the International Ophiolite Symposium, Cyprus 1979, Institute of Mining and Metallurgy, 261-272.

[40]   Pearce, J.A. and Cann, J.R. (1971) Ophiolite Origin Investigated by Discriminants Analysis Using Ti, Zr and Y. Earth and Planetary Science Letters, 12, 339-349.
http://dx.doi.org/10.1016/0012-821X(71)90220-2

[41]   Pearce, J.A. and Cann, J.R. (1973) Tectonic Setting of Basic Volcanic Rocks Determined Using Trace Element Analyses. Earth and Planetary Science Letters, 19, 290-300.
http://dx.doi.org/10.1016/0012-821X(73)90129-5

[42]   Pearce, T.H., Gorman, B.E. and Birkett, T.C. (1975) The TiO2-K2O-P2O5 Diagram: A Method of Discriminating between Oceanic and Non-Oceanic Basalts. Earth and Planetary Science Letters, 24, 419-426. http://dx.doi.org/10.1016/0012-821X(75)90149-1

[43]   Pearce, T.H., Gorman, B.E. and Birkett, T.C. (1977) The Relation between Major Element Chemistry and Tectonic Environment of Basic and Intermediate Volcanic Rocks. Earth and Planetary Science Letters, 36, 121-132. http://dx.doi.org/10.1016/0012-821X(77)90193-5

[44]   Pearce, J.A. and Norry, M.J. (1979) Petrogenetic Implications of Ti, Zr, Y and Nb Variations in Volcanic Rocks. Contributions to Mineralogy and Petrology, 69, 33-47. http://dx.doi.org/10.1007/BF00375192

[45]   Wood, D.A., Tarney, J., Varet, J., Saunders, A.D., Bougault, H., Joron, J.L., Treuil, M. and Cann, J.R. (1979) Geochemistry of Basalts Drilled in the North Atlantic by IPOD Leg 49: Implications of Mantle Heterogeneity. Earth and Planetary Science Letters, 42, 77-79. http://dx.doi.org/10.1016/0012-821X(79)90192-4

[46]   Floyd, P.A. and Winchester, J.A. (1975) Magma Type and Tectonic Setting Discrimination Using Immobile Elements. Earth and Planetary Science Letters, 27, 211-218.
http://dx.doi.org/10.1016/0012-821X(75)90031-X

[47]   Wood, D.A. (1980) The Application of a Th-Hf-Ta Diagram to Problems of Tectonomagmatic Classification and to Establishing the Nature of Crustal Contamination of Basaltic Lavas of the British Tertiary Volcanic Province. Earth and Planetary Science Letters, 50, 11-30.
http://dx.doi.org/10.1016/0012-821X(80)90116-8

[48]   El-Akhal, H. (2004) Contribution to the Petrology, Geochemistry and Tectonic Setting of the Basalt Flows of the Umm-Qais Plateau, North Jordan.

[49]   Wilkison, J.F.G. (1986) Classification and Average Chemical Composition of Common Basalts and Andesites. Journal of Petrology, 27, 181-194.

[50]   Goudarzi, G.H. (1980) Structure: Libya. In: Salem, M.J. and Busrewil, M.T., Eds., The Geology of Libya, Vol. 3, Academic Press, London, 879-892.

[51]   Klitzsch, E. (1971) The Structural Development of Parts of North Africa since Cambrian Times. In: Gray, C., Ed., First Symposium on the Geology of Libya, Faculty of Science, University of Libya, Tripoli, 253-262.

[52]   El-Makhrouf, A.A. (1988) Tectonic Interpretation of Jabal Eghei Area and Its Regional Application to Tibesti Orogenic Belt, South Central Libya. Journal of African Earth Science, 7, 945-967. http://dx.doi.org/10.1016/0899-5362(88)90009-7

[53]   Anketell, J.M. and Ghellali, S.M. (1991) A Palaeogeologic Map of the Pre-Tertiary Surface in the Region of the Jifarah Plain and Its Implication to the Structural History of Northern Libya. In: Salem, M.J., Busrewil, M.T. and Ben Ashour, A.M., Eds., Geology of Libya, Vol. 7, Elsevier, Amsterdam, 2681-2687.

[54]   Mikbel, S.R. (1977) Basement Configuration and Structure of West Libya. Libyan Journal of Science, 7A, 19-33.

[55]   Jurak, L. (1978) Geologic Map of Libya 1:250,000, Sheet: Jabal Al Hasawanah NH 33-14. Explanatory Booklet. Industrial Research Centre, Tripoli, 74-100.

[56]   Le Bas, M.J., LeMaitre, R.W., Strecheisen, A.L. and Zanettin, B. (1986) A Chemical Classification of Volcanic Rocks Based on the Total Alkali-Silica Diagram. Journal of Petrology, 27, 745-750. http://dx.doi.org/10.1093/petrology/27.3.745

[57]   Gafeer, A.S. (2007) The Petrology and Geochemistry of Gharyan Volcanic Province, NW Libya. Unpublished MSc Thesis, The University of Garyounis, Benghazi.

[58]   Aboazom, A.S., Asran, A.S.H., Abdel Ghani, M.S. and Farhat, E.S. (2006) Geologic and Geochemical Constraints on the Origin of Some Tertiary Alkaline Rift Volcanics, Gharyan Area, Northwestern Libya. Assiuit University Journal of Geology, 35, 25-47.

[59]   Almond, D.C., Busrewil, M.T. and Wadsworth, W.J. (1974) The Gharian Tertiary Volcanic Province of Tripolatania, Libya. Geological Journal, 9, 17-28. http://dx.doi.org/10.1002/gj.3350090102

[60]   Hegazzy, A.H. (1999) Tertiary Volcanics in Libya: Evidence for the Direction and Rate of the African Plate Motion. Proceedings of the Fourth International Conference on Geochemistry, Alexandria University, Egypt, 401-419.

[61]   Piccoli, C. (1971) Outlines of Volcanism in Northern Tripolitania. In: Gray, C., Ed., Symposium on the Geology of Libya, Fac. Sci., Univ. Padova.

[62]   Mullen, E.D. (1983) MnO/TiO2/P2O5: A Minor Element Discriminant for Basaltic Rocks of Oceanic Environments and Its Implications for Petrogenesis. Earth and Planetary Science Letters, 62, 53-62. http://dx.doi.org/10.1016/0012-821X(83)90070-5

 
 
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