Akademik Veri Yönetim Sistemi
ITALIAN JOURNAL OF GEOSCIENCES, cilt.142, sa.3, ss.449-473, 2023 (SCI-Expanded)
The Cenozoic Gharyan Volcanic Province (GVP) represents one of the four major igneous districts of Libya,
spreading over an area of ~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 40Ar/39Ar 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~2 to ~12% partial
melting of a heterogeneous sub-lithospheric mantle close to the spinel-garnet transition at ~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 40Ar/39Ar 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 ~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 40Ar/39Ar ages between “plateau” and
“late” basalts indicates that the existence of two distinct volcanic phases should be reconsidered.