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Geochemistry and (sub 40) Ar/ (sub 39) Ar ages of late Cenozoic basaltic rocks from Gharyan volcanic province, NW Libya

Abdelmoniem Masoud, Abdelsalam Elshaafi, Ozgur Karaoglu, Alsedik Abousif and Michele Lustrino
Geochemistry and (sub 40) Ar/ (sub 39) Ar ages of late Cenozoic basaltic rocks from Gharyan volcanic province, NW Libya
Italian Journal of Geosciences (October 2023) 142 (3): 449-473

Abstract

The Cenozoic Gharyan Volcanic Province (GVP) represents one of the four major igneous districts of Libya, spreading over an area of approximately 4,500 km2. Despite the location of GVP close to major population centres in northwest Tripoli, the number of studies on the origin of this magmatism is relatively limited. Here, we discuss whole-rock geochemical data and present a new mineral chemistry and a (super 40) Ar/ (super 39) Ar geochronology study of the basaltic rocks of GVP. The mineralogical and geochemical differences of the two types of basalts identified in literature, defined as "plateau" and "late" basalts cannot be related to fractional crystallisation of a common parent magma. The two groups of basaltic rocks are better interpreted as liquids generated from the same mantle source experiencing different degrees of partial melting, with the late-stage basalts representing lower degrees of melt extraction, without indication of crustal contamination. Trace element constraints support an origin from approximately 2 to approximately 12% partial melting of a heterogeneous sub-lithospheric mantle close to the spinel-garnet transition at approximately 70-90 km depth. Trace elements and Sr-Nd isotopic compositions of the Gharyan basaltic rocks overlap the other Cenozoic volcanic rocks of central Libya (e.g., Al Haruj volcanic province) and southern Italy (e.g., Etna and Pantelleria), lacking the presence of the enriched mantle component identified in other North African Cenozoic basaltic provinces. The new high precision (super 40) Ar/ (super 39) Ar age determinations indicate roughly simultaneous eruption ages of the two basaltic lava series, mostly in the 5.4-3.8 Ma range, with plateau basalts being statistically slightly older than the late stage, but with a large overlap. The dating of a dyke to approximately 28 Ma indicates the presence of an older Oligocene volcanic phase, whose products have been almost entirely eroded. The youngest age reported in this study indicates that volcanic activity continued until latest Pliocene (2.67 Ma). The overlap of (super 40) Ar/ (super 39) Ar ages between "plateau" and "late" basalts indicates that the existence of two distinct volcanic phases should be reconsidered.


ISSN: 2038-1719
EISSN: 2038-1727
Serial Title: Italian Journal of Geosciences
Serial Volume: 142
Serial Issue: 3
Title: Geochemistry and (sub 40) Ar/ (sub 39) Ar ages of late Cenozoic basaltic rocks from Gharyan volcanic province, NW Libya
Affiliation: Sebha University, Department of Earth Sciences, Sebha, Libya
Pages: 449-473
Published: 202310
Text Language: English
Publisher: Societa Geologica Italiana, Rome, Italy
References: 94
Accession Number: 2023-086644
Categories: Igneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N31°00'00" - N32°49'60", E12°00'00" - E13°00'00"
Secondary Affiliation: Benghazi University, Department of Earth Sciences, LBY, LibyaEskisehir Osmangazi University, TUR, TurkeySapienza Universita di Roma, ITA, Italy
Country of Publication: Italy
Secondary Affiliation: GeoRef, Copyright 2023, American Geosciences Institute. Abstract, Copyright, Societa Geologica Italiana. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2023
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