The petrogenesis of pyroxenites containing octahedral graphite and associated mafic and ultramafic rocks of the Beni Bousera peridotite massif, N. Morocco

The Beni Bousera peridotite massif, N. Morocco, contains pyroxenite layers of varied mineralogy, including graphitic garnet clinopyroxenite ( GGP ) layers. The graphite in these rocks occurs as octahedral multi-crystalline aggregates and other forms of cubic symmetry. Scanning electron microscopy and X-ray diffraction studies indicate that the graphite aggregates represent graphitized diamonds. Minor Na in coexisting garnets confirm ran origin in the diamond stability field. However, other mineral chemical data from the peridotites and pyroxenites indicate major sub-solidus re-equilibration of the silicate assemblages. Major and trace element analyses indicate the peridotites are residues of partial melting (5-30 %) in the spinel and possibly garnet stability fields. Some peridotites have suffered Fe and/or LREE enrichment. The pyroxenite suite crystallized as veins/dikes in the peridotites and show fractionation trends controlled by OPX, CPX, garnet and possibly spinel. The LREE depleted nature of the pyroxenite suite, combined with their highly variable incompatible element contents which do not correlate with fractionation indices such as Mg No., preclude their derivation from the host peridotites and require a chemically heterogeneous source/sources. Positive and negative Eu anomalies in the pyroxenites suggest their derivation from a low pressure precursor. Sr, Pb and Nd isotope analyses of the peridotites reveal large magnitude, small scale ( sub-km ) heterogeneities. Pyroxenites show even greater isotopic diversity and a decoupling of trace element-isotope systematics which indicate a recent melting event Sr, Pb and Nd isotopes indicate both peridotites and pyroxenites have experienced complex, long term evolution. The extreme isotopic diversity of the pyroxenites, with Pb isotope compositions that plot both to the left and right of the geochron, with high Δ7/4 and Δ8/4 values, are consistent with their derivation as melts of subducted oceanic crust plus less than 1% sediment, over 1 Ga ago. This interpretation is supported by pronounced oxygen isotope variability ( 8 ^ 18 0 = +4.9 to +9.3 %o ) suggesting the oceanic crustal source/s were hydrothermally altered before subduction. Hydrothermal alteration augmented Sr and Pb isotopicheterogeneity in the pyroxenites. If the isotopically light graphite in the GGP ( 8^13 C = -17 to -27 %o ) represents the carbon isotopic composition of the precursor diamonds, the original diamonds may have formed from subducted crustal ( kerogenous?) carbon. A model is proposed invoking subduction of hydrothermally altered oceanic crust and lithosphere, together with minor amounts of sediment (< 1 % ) into the asthenosphere over 1 Ga ago. The subducted oceanic slab descended to the 670km seismic discontinuity and "ponded” to form a megalith. Thermal equilibration of this megalith induced diapirism into the asthenosphere. Melting during ascent may have formed the pyroxenite layers and refertilized some of the peridotites. Asthenospheric upwelling during a major Neogene extensional event initiated emplacement of pyroxenite veined peridotitic mantle into the N. African, crust. Recent, small degree partial melting during ascent into the crust decoupled parent-daughter isotope systematics in the pyroxenites and peridotites. Graphitization of diamond in the GGP may also have occurred at this time. Pyroxenites containing graphitized diamonds in an orogenic peridotite massif provide evidence in support of a non-volcanic source for diamonds of unexplained provenance which occur in, or close to, major tectonic collision zone

From Koine to Romanitas: The numismatic evidence for Roman expansion and settlement in Bulgaria in antiquity (Moesia and Thrace, ca. 146 BC – ad 98/117)

The primary goal of this thesis is to collect, record and interpret the available coin evidence from the territory of modern Bulgaria during the late Hellenistic and early Roman Imperial period, from an archaeological, historical and numismatic perspective. In so doing the work documents the transition and integration of the monetary system of ancient Thrace to that of the Roman world. The evidence examined covers over 250 years, from the establishment of the province of Macedonia in 146 BC down to the reign of Trajan (AD 98-117). Of foremost importance in this process are the introduction, distribution and use of the denarius in the local coin market. The evidence under study was collected from the area of ancient Moesia and Thrace, an area recognized as a frontier zone in the early Roman Empire. Previously Thrace was never the subject of a comprehensive numismatic study that integrated the existing archeological and historical record for such a critical period of time. The purposely studied coin finds (both hoards and single coins, over 48,000 pieces) allowed for the application of statistical analysis to the coin data, revealing important military, economic and fiscal tendencies. The results document a culture well accustomed to the use of coins as means of payment long before the arrival of the Roman currency. Given these circumstances, it is no surprise that as denarii were introduced during the 1st century BC, the market quickly adjusted to new economic relations. Tracing the regional use and distribution of coins, the study bears witness to how local communities benefited from their strategic location and native resources. The main contribution of this work lies in the systematic comparison between the Late Hellenistic, Thracian, Celtic and Roman coinages that circulated together in a region that was of great strategic importance to the Roman Empire. Mechanisms of introduction and acceptance of Roman coins as financial tools have been documented and interpreted both from a chronological and geographical standpoint. Based on comprehensive analyses, this thesis concludes that the nature of the Thracian and Moesian society and economy, as well as the supply of coins, followed the Imperial and interregional trends as an integral part of the Roman Empire