Geophysical Studies of North African Cenozoic Volcanic Areas: III. Garian, Libya

Abstract

Paleomagnetic and K/Ar whole rock absolute age data are described for material from the Garian area of Libya, centered at 13°E, 32°N. Within-unit cleaned paleomagnetic directions from the essentially unaltered lavas are very well defined and can almost certainly be taken as reliable measurements of the geomagnetic field direction during the initial cooling of each flow. However, the distributions of mean direction, from which the effect of repeated sampling of the field at one time has been removed, does not suggest that a reversing axial dipole field has been recorded in a representative manner. Both N and R groups of directions are azimuthally elongated, and the average poles for the N and R groups differ by 21°, or four times the 95% level uncertainty for each average pole. A number of possible physical explanations for the paleomagnetic results are discussed. The conventional overall average pole at 88°N, 123°E, δp: 3°, δm: 7 °does not differ significantly from the geographic pole, a result which agrees closely with that of Schult and Soffel (1973). However, the value of these overall average poles in estimating absolute plate motion must await an understanding of the sources of the asymmetries in the paleomagnetic data.

Palaeolatitudes from DSDP Leg 73 sediment cores. implications for the apparent polar wander path for Africa during the late Mesozoic and Cenozoic

“…(b) Some poles included in previous compilations have been re-dated. The Libyan basalts, initially thought to be Oligocene have now been re-dated as Pliocene (Ade-Hall et al 1975).…”

Quantifying Asthenospheric and Lithospheric Controls on Mafic Magmatism Across North Africa

“…Different forms Figure 1 for location). Black patches = volcanic fields <30 Ma; colored circles = loci of volcanic samples described and analyzed in this study; labeled boxes = names of individual volcanic fields with ranges of radiometric dates taken from Ade-Hall et al (1975a), Bardintzeff et al (2012), Busrewil and Esson (1991), Cvetković et al (2010), Deniel et al (2015), Jurák (1978), Masoud (2014), Radivojević et al (2015), and Schult and Soffel (1973); dotted line = outline of Sirt Basin taken from Abdunaser and McCaffrey (2015). of sample screening are used to mitigate the effects of crystal fractionation, of lithospheric contamination, and of source heterogeneity.…”

The central part of the Jebel Nefusa volcano (Libya) survey map, age relationship and preliminary results

“…The doubts regarding the high basalt ages of PlCCOLI, expressed in the paper of ADE-HALL et al (1975), have to be confirmed. Unfortunately however, the determinations of ADE-HALL et al (1975) cover not the variety of the most common volcanic types of the Jebel Nefusa.…”

“…The recent age determinations of ADE-HALL et al (1975) yield only very young ages of flood basalts. The doubts regarding the high basalt ages of PlCCOLI, expressed in the paper of ADE-HALL et al (1975), have to be confirmed.…”

“…Combining the data of PlCCOLI (1971) and ADE-HALL et al (1975) and the field results, the age relationships could be as follows: From the age data of PlCCOLI therefore only the figure relating the flood and valley basalts are not here accepted. These values are, according PlCCOLI, more than 50 m.y., which seems unreasonably high, not only due to the faets shown by Fig.…”