Geochronology

The felsic lavas of the Bamenda Mountains, in the main part of the Cameroon Volcanic Line, are mainly represented by trachytes, with subordinated benmoreites and alkaline to peralkaline rhyolites. New K–Ar geochronological data define two main volcanic episodes, the first one between 18 and 22Ma, and the second one from 12.5 to 13.5Ma. Geochemical data indicate that these felsic rocks

We present palaeoenvironmental, geomorphological, archaeological, and place-name data which allow a holistic assessment of the history of landscape change on Sandoy, Faroe Islands, especially in terms of the changes that occurred in response to the colonization of the island by humans. In contrast to other situations in the North Atlantic region, there is considerable continuity in the patterns and processes of landscape evolution across the initial

Large projectiles impacting the Earth will cause severe shock heating and chemical reprocessing of the Earth's atmosphere. This occurs during atmospheric entry and, more importantly, as a result of the supersonic plume ejected on impact. In particular, very large amounts of nitric oxide would result from the impact of the putative Cretaceous-Tertiary bolide(s). We present models of the shock chemistry, the conversion of NO to NO 2 and thence to nitrous and nitric acids, and the global dispersion of the NO 2 and acids. Two plausible projectiles are considered: an ice-rich long-period comet and a much smaller rock-metal asteroid. The comet produces semi-global atmospheric NO 2 mixing ratios of 0.1% while the asteroid produces these high mixing ratios only in the immediate region of the impact. The comet produces concentrated nitrous and nitric acid rain with a pH ~ 0-1.5 globally. The asteroid produces rain with a pH ~ 0-1 near the impact and-4-5 globally. Immediate environmental effects of these nitrogen species include inhibition of photosynthesis due to extinction of solar radiation by NO 2, foliage damage due to exposure to NO 2 and HNO 3, toxicosis resulting from massive mobilization of soil trace metals, and respiratory damage due to exposure to NO 2. The acid rain decreases the pH of the oceanic mixed layer affecting the stability of calcite with important implications for the survival of calcareous-shelled organisms and for exhalation of CO, from the mixed layer to the atmosphere. Longer-term environmental effects perhaps-1000 years in duration include a global warming due to the sudden CO 2 injection and the simultaneous extinction of the ocean microorganisms which normally help remove CO 2 from the atmosphere-mixed layer system. Havens for survival include carbonate-buffered lakes and burrows. This acid rain theory therefore serves to explain the peculiar selectivity of the extinctions seen at the Cretaceous-Tertiary boundary. The first few years of acid rain will lead to massive weathering rates of continental soils characterized by large ratios of the relatively insoluble metals (e.g. Be 2+, AI ~, Hg 2., Cu*, Fe 2+, Fe 3+, T13+, Pb 2+, Cd 2~, Mn 2., Sr 2.) to the more soluble metals (Ca 2 +, Mg 2 +) which should have left a clear signal in the fossils of neritic organisms and in unperturbed neritic sediments near river deltas if such sediments still exist for the Cretaceous-Tertiary time frame.

Granite plutons of the Whypalla Supersuite in the Butchers Hill-Helenvale region of north Queensland were intruded into the upper crust of the Hodgkinson Formation during contractional deformation associated with the Permian-Triassic Hunter-Bowen Orogeny. A four-stage structural history has been resolved for the area, with fabric overprinting relationships, porphyroblast-matrix microstructural geometries and isotopic ages being consistent with granite emplacement during D 4 shortening at ca 274 Ma. Microstructural relationships suggest the possibility of a minor syn-D 3 phase of granite emplacement. The deformation-emplacement history of the Butchers Hill-Helenvale area is consistent with that recognised regionally for the Hodgkinson Province, indicating province-wide synchronous syntectonic granite intrusion during a major phase of contractional deformation. Intense syn-emplacement deformation partitioning was ongoing in the country rocks during progressive D 4 and was associated with upward translation of country rock from the microscale to the macroscale along D 4 cleavages and shears. Kinematic indicators show that this progressive uplift, at the scale of the area examined, was east-side-up.

The northern segment of the Palaeoproterozoic Itabuna-Salvador-Curaçá collisional orogen in the São Francisco craton (Brazil) comprises two high-grade terranes separated by the 150 km long, N-S-trending Itiúba Syenite. The Curaçá terrane to the west contains copper sulphide deposits hosted by hypersthenite-norite complexes (e.g. Caraíba body), whereas the Jacurici terrane to the east contains chromite deposits hosted by peridotite-norite sills (e.g. Medrado body). SHRIMP U-Pb dating of zircons, combined with a significant major element compositional gap indicates that the Caraíba (2580±10 Ma) and the Medrado (2085 ± 5 Ma) mafic-ultramafic complexes are not related by fractional crystallisation as previously thought. Depleted-mantle Nd model ages for the regional gneisses are also distinct, with the Curaçá terrane having younger ages (2.4-2.8 Ga) than the Jacurici terrane (2.9-3.2 Ga), suggesting that they represent two independent fragments of continental crust accreted during the Palaeoproterozoic orogeny. Emplacements of the Itiúba Syenite (ca. 2084 Ma) and of the Medrado complex were apparently coeval, probably controlled by orogen-parallel block displacement, or escape tectonics, following continent-continent collision.

The results of geoarchaeological  investigations at Pharo Village, a Fremont hamlet situated on a large alluvial fan in central Utah, are discussed in order to reveal ways in which landform dynamics contributed to the rise of Fremont occupation there as well as to the site's eventual abandonment.  Cutbanks along Pharo Creek, the stream adjacent to Pharo Village, were mapped and sampled during fieldwork in 2013.  Field and subsequent laboratory analysis resulted in reconstruction of the alluvial geochronology of the stream and geomorphological history of its adjacent landforms.  Carbon samples from mapped strata and buried paleosols were radiocarbon dated and correlated to additional dates generated from the site's archaeological component housed at the Natural History Museum of Utah (NHMU). Projectile points in the NHMU collection were also analyzed in order to further refine when site occupations occurred.  Redating of the site indicate Pharo Village had three periods of occupation, with two of three site abandonments correlating with regional drought events. Buried soils in mapped sections indicate a period of stability on the landform where Pharo Village is located prior to and likely during the site's occupation, suggesting landform stability encouraged Fremont use of the site. The final abandonment of the site ca. 600 cal BP occurred before or during a transition to a more active geomorphic environment marked by flooding and considerable deposition.  This abandonment is also consistent with the general temporal span for the cessation of Fremont lifeways in the region and a major regional megadrought.

Although most data suggest that the India–Eurasia continental collision began approx 45–55 Myr ago, the architecture of the Himalayan–Tibetan orogen is dominated by deformational structures developed in the Neogene period (< 23 Myr ago). The stratigraphic record and thermochronometric data indicate that erosion of the Himalaya intensified as this constructional phase began and reached a peak around 15 Myr ago. It remained high until approx 10.5 Myr ago and subsequently slowed gradually to approx 3.5 Myr ago, but then ...

This report documents several new findings concerning the geology and mineral potential of the central East Tintic Mountains, Utah. For example, fission-track ages and 40Ar/39Ar ages which we report suggest that some of the
volcanism and alteration in this area is as old as 37.4 to 35.3 Ma. This early episode of volcanism was contemporaneous with lacustrine deposition; the overlying volcanic rocks and cross-cutting intrusions range in age from about 34.5 to 33.6 Ma. This implies that a large caldera related to the eruption of the younger Packard Quartz Latite and Fernow Quartz Latite is not present in this area . However, our data suggest that a smaller caldera related to the eruption of the tuff member of the Copperopolis Latite may be present. We note that many monzonite dikes and intrusions in this area are hornblende bearing and are correlative in modal and chemical composition with the productive Silver City Stock rather than the barren Sunrise Peak Stock. The large areas of hydrothermal alteration which surround these intrusions
exhibit many similarities to the well-studied alteration halos in the East Tintic District. The age, composition, and field relationships of the post-lacustrine volcanic rocks suggest that they may represent, in part, the extrusive equivalents of the monzonite dikes and Silver City Stock. Our work suggests that the Silver City Stock and related intrusions may be part of one of the youngest (33.6 ± 0.2 Ma) igneous events in the central East Tintic Mountains, but not as young as previously suggested (ca. 31.5 Ma). In addition, our recent work has documented the existence of unusually large (and abundant) magmatic sulfides in lava vitrophyres and vent-facies biotite latite dikes, which are the surface expressions of the Silver City Quartz Monzonite intrusions in this area. In addition, preliminary analytical data suggest that the sulfides host most (-75%) of the Ag present in the latites. The East Tintic Mountains are potentially the first locality, worldwide, where Ag in mesothermal veins can be demonstrated to be derived from degassed Ag-bearing magmatic sulfides. Consequently, the central East Tintic
Mountains are a favorable area for exploration for Ag (Pb-Zn-Cu-Au) ore bodies because: 1) productive monzonite intrusions are present, and 2) Paleozoic rocks favorable for ore deposition may be present beneath relatively thin volcanic cover because the area is not entirely enclosed within a caldera.

Optically stimulated luminescence (OSL) dates are reported for silts and very fine sands believed to be loessic sediments from northwest England. At three sites loessic sediments were initially interpreted as primary aeolian deposits, and at two other sites as loess incorporated into the matrix of cemented scree. However, the results of OSL dating indicate a more complex pattern of accumulation than originally hypothesized and have prompted reconsideration of these materials. Whatever the process(es) and underlying cause(s), it is evident that significant amounts of soil erosion occurred on the limestone uplands earlier than previously thought. All but one of the ages fall entirely within the Holocene period and suggest that these deposits contain reworked, rather than primary loess. Four of the five sites are characterized by non-Gaussian dose distributions, and consequently equivalent doses have been estimated using a range of appropriate age models. The implications of differences in the ages derived from the fine silt and fine sand fractions of the samples are considered. Three processes, namely aeolian transport, overland flow and subsoil piping, are invoked to account for the reworking of loess, although their relative contributions cannot be quantified. At one site the inclusion of limestone clasts within the reworked loess strongly suggests that the sediment can be regarded as loess-derived colluvium. Human impacts on the landscape and climate shifts, either separately or in combination, are considered to have been the most likely mechanisms that triggered loess erosion.

The Serido Group is a deformed and metamorphosed metasedimentary sequence that overlies early Paleoproterozoic to Archean basement of the Rio Grande do Norte domain in the Borborema Province of NE Brazil. The age of the Serido Group has been disputed over the past two decades, with preferred sedimentation ages being either Paleoproterozoic or Neoproterozoic. Most samples of the Serido Formation, the upper part of the Serido Group, have Sm–Nd TDM ages between 1200 and 1600 Ma. Most samples of the Jucurutu Formation, the lower part of the Serido Group, have TDM ages ranging from 1500 to 1600 Ma; some basal units have TDM ages as old as 2600 Ma, reflecting proximal basement. Thus, based on Sm–Nd data, most, if not all, of the Serido Group was deposited after 1600 Ma and upper parts must be younger than 1200 Ma. Cathodoluminescence photos of detrital zircons show very small to no overgrowths produced during ca. 600 Ma Brasiliano deformation and metamorphism, so that SHRIMP and isotope d...

Proglacial Lake Humber is of UK national significance in terms of landscape drainage and development of the British Ice Sheet (BIS) during Marine Isotope Stage 2 (MIS 2), yet it is poorly understood in terms of its dynamics and timing. Sands and gravels exposed at Ferrybridge, West Yorkshire, UK, are interpreted as part of the Upper Littoral sands and gravels related to a high-level Lake Humber, which inundated the Humber Basin to $30 m OD during MIS 2. Excavations exposed well-rounded gravels of local origin extending downslope from the 27.5 m OD contour and interbedded sands and fine gravels, which are interpreted as the coarse littoral deposits and nearshore associated deposits. A sample from the distal sands returned an Optically Stimulated Luminescence age of 16.6AE1.2 kyr, providing the first direct age for the high-level lake and for when North Sea Basin ice must have blocked the Humber Gap. An underlying sequence included a diamicton dated to after 23.3 AE1.5 kyr and before 20.5AE1.2 kyr, indicating that the Late Devensian ice reached at least 15 km south of the Escrick Moraine prior to the high-level lake. Previous to both the high-level lake and this ice advance, loess found at the two sites investigated indicates a long period of loess deposition earlier in MIS 2. These new data for the history of Lake Humber are discussed in the context of ice-marginal oscillations in both the Vale of York and the North Sea Basin.

This study deals with the geochronological, geoarchaeological, sedimentological and geomorphological analyses of sandy Pleistocene fluvial deposits exposed throughout the Prados-Guatén Depression, occupying the wide drainage divide of the Guadarrama and Jarama rivers draining towards the Tagus River (SW Madrid, Central Spain). Pleistocene fluvial deposits within the depression record two different fluvial systems draining the zone during the Pleistocene. Older fluvial deposits (T1), thick stacked arkosic sand sequences (w15e17 m) with fossil fauna attributable to the Lower Pleistocene (c. 1.0e0.9 Ma; Mammuthus meridionalis NESTI), exposed at elevations of þ15e40 m above the present Guatén stream thalweg. This terrace was deposited by an ancient fluvial system draining the Depression north to south, flowing directly to the Tagus (Paleo-Manzanares). Overlapping the older ones, the younger deposits studied are inset fluvial terraces at þ13e16 m (T2) and þ8 m (T3). T2 Upper-Middle Pleistocene (500e200 ka) fauna, Equus ferus cf. Mosbachensis, is related with the abandonment of the valley, the onset of a stage of relevant intra-valley dissection, and subsequent refilling linked to the early organization of the present drainage leading to the development of T3. Paleomagnetic data from T2 and T3 terraces display an overall normal "Brunhes" polarity, although anomalous reverse polarities are recorded in the younger terrace (T3). TL and OSL dates range between c. >126e75 ka for T2 (MIS 5) and c. 20e17 ka for T3 (MIS 2), indicating a mainly Upper Pleistocene age for the development of these two more recent terraces. The dates obtained indicate that the establishment of the present divergent fluvial arrangement within the Prados-Guatén Depression started during the Middle-Upper Pleistocene transition, after it was abandoned by the Lower-Middle Pleistocene Paleo-Manzanares fluvial system (T1). T2 contains a variety of Lower to Middle Palaeolithic flint flaking products, indicating chronocultural transition during the Upper Pleistocene in the area, correlated with a drastic change in the fluvial landscape from the end of MIS 5 (<75 ka).

DateView is a freeware desktop database system for the structured storage and retrieval of geochronological information. It provides a user-friendly interface for constructing queries based on information in the database so as to extract information on specific units, isotope systems, age interpretations, provinces, terranes, reference sources and many other characteristics which geochronologists and geologists might require. Once a subset of the records in the database has been selected, users may choose from several forms of graph so as to better visualise the data. Available graphs include probability histograms, age versus initial ratio or epsilon, and age versus closure temperature. Simple locality (latitude vs longitude) graphs are also available. Grouping of data by interpretation or age interval in the graphs is user customizable. The database may also be shared with colleagues on an intranet. r $ Code on server at http://www.iamg.org/CEEditor/ index.htm Ã

The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican Volcanic Belt (TMVB), an area that records a long history of magmatic and tectonic activity. The oldest rocks that crop out in the area are early-Oligocene (32.7 ± 0.2 Ma) dioritic to granitic (60–72 wt. % SiO2) plutons intruded by younger to contemporaneous (30.3 ± 0.1 and 33.3 ± 0.7 Ma) aplitic (76–78 wt. % SiO2) dikes and mineralized veins. Volcanic rocks related to these intrusives form a thick sequence exposed in cliffs, from the base of which an altered andesite (58 wt. % SiO2) was collected. The nearby epithermal Cu-mineralization of the Inguarán mining area to the southeast is also related to this Tertiary volcanic episode. The oldest expression of the TMVB in this area is represented by Pliocene (3.2–2.4 Ma) basaltic andesite to andesite (53–63 wt. % SiO2) lavas (with pyroxene ± olivine) forming extensive mesas, eroded mounds, and thick elongate flows, that were unconformably deposited on top of the Oligocene rocks. Their emplacement was followed by erosion approximating a rate of 100 m/Ma over the past 3 Ma. This led to the formation of an inverted topography reflecting the higher resistance to erosion of these lavas that were originally deposited in valleys and today constitute prominent mesas. During the last 1 Ma, at least twenty-six monogenetic scoria cones formed in the study area, erupting about 10.2 km3 of lava and pyroclastics dominantly composed of olivine and pyroxene-bearing andesites (61 vol. % DRE), lesser basaltic andesites (30 vol. % DRE), and a minority of olivine-rich basalts (10 vol. % DRE). These eruptive products include the K-rich basaltic trachyandesites of Cerro La Pilita, a scoria and lava cone located close to Jorullo. The ≤ 27 ka San Hilario and Esmeralda lavas, which are located 13 km southeast of Jorullo, are the southernmost eruptive products of the TMVB and also the youngest volcanoes after Jorullo in this area. Mapping of main faults and scoria cone alignments on regional and local scales reveals that the ascent of dikes feeding Quaternary eruptions in the Jorullo area was controlled by west-northwest and west-southwest basement structures, northeast-oriented subduction-related horizontal compressional stress probably associated with crustal fractures, and a major northwest-trending seismically-active fault zone that passes near Paricutin and Jorullo.

Carbonate is abundant in many Neolithic tells and is a potentially useful archive for dating and climate reconstruction. In this paper, we focus on the mineralogy, radiocarbon dating, and stable isotope systematics of carbonate in hackberry endocarps. Hackberry fruits and seeds are edible in fresh and stored forms, and they were consumed in large quantities in many Neolithic sites in the Near East, including the site of our study, Aşıklı Höyük in central Anatolia, an Aceramic Neolithic tell occupied from about 9.4 to >10.3 BP (7.4 to >8.3 BCE). Detailed 14 C age control provided by archaeological charcoal permits a test of the fidelity in 14 C dating of hackberry endocarps. Modern endocarps and leaves yield fraction modern 14 C values of 1.050-1.066, consistent with levels present in the atmosphere when sampled in 2009. On the other hand, archaeological endocarps yield consistently younger ages than associated charcoal by ca. 130 14 C years (ca. 220 calendar years) for samples about 10,000 years old. We speculate this is caused by the slight addition of calcite or recrystallization to calcite in the endocarp, as detected by scanning electron microscopy. Subtle addition or replacement of calcite by primary aragonite is not widely recognized in the 14 C community, even though similar effects are reported from other natural carbonates such as shell carbonate. This small (but consistent) level of contamination supports the usefulness of endocarps in dating where other materials like charcoal are lacking. Before dating, however, hackberries should be carefully screened for mineralogical preservation and context. We examined the carbon and oxygen isotopic systematics of the fossil endocarps to try to establish potential source areas for harvesting. Most of the hackberries are enriched in 18 O compared to local water sources, indicating that they were drawing on highly evaporated soil water, rather than the local (perched and regional) water table sampled in our study. Isotopic evidence therefore suggests that most but not all of the hackberries were harvested from nearby mesas well above the local streams and seeps fed by the water table.

In this shortnote, we present the results of a geochronological study of the last eruption in the volcanic region of the Garrotxa (NE Iberian Peninsula). Four 14C analysis of organic matter contained in palaeosols located under volcanic pyroclastic fall deposits of the Croscat volcano were made. The samples gave ages between 13160 and 15710 years cal BP, and are in accord with our palynological analysis and climate reconstruction at that time. The ages that we report are the youngest obtained for volcanic activity in the Iberian Peninsula.

We report new major element, trace element, isotope ratio, and geochronological data on the Galfipagos Archipelago. Magmas erupted from the large western volcanos are generally moderately fractionated tholeiites of uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic basanitoids. While these volcanos do not form a strictly linear age progressive chain, the ages of the oldest dated flows on any given volcano do form a reasonable progression from youngest in the west to oldest in the east, consistent with motion of the Nazca plate with respect to the fixed hotspot reference frame. lsotope ratios in the Galfipagos display a considerable range, from values typical of mid-ocean ridge basalt on Genovesa (87Sr/86Sr: 0.70259, end: +9.4, 206pb/204pb: ! 8.44), to typical oceanic island values on Floreana (87Sr/86Sr: 0.70366, oeNd: +5.2, 206pb/204pb: 20.0). La/Sm N ranges from 0.45 to 6.7; other incompatible element abundances and ratios show comparable ranges. Isotope and incompatible element ratios define a horseshoe pattern with the most depleted signatures in the center of the Galfipagos Archipelago and the more enriched signatures on the eastern, northern, and southern periphery. These isotope and incompatible element patterns appear to reflect thermal entrainment of asthenosphere by the Galfipagos plume as it experiences velocity shear in the uppermost asthenosphere. Both north-south heterogeneity within the plume itself and regional variations in degree and depth of melting also affect magma compositions. Rare earth systematics indicate that melting beneath the Galfipagos begins in the garnet peridotite stability field, except beneath the southern islands, where melting may occur entirely in the spinel peridotite stability field. The greatest degree of melting occurs beneath the central western volcanos and decreases both to the east and to the north and south. Sis. 0, FeB. 0, and NaB. 0 values are generally consistent with these inferences. This suggests that interaction between the plume and surrounding asthenosphere results in significant cooling of the plume. Superimposed on this thermal pattern produced by plume-asthenosphere interaction is a tendency for melting to be less extensive and to occur at shallower depths to the south, presumably reflecting a decrease in ambient asthenospheric temperatures away from the Galfipagos Spreading Center.

A group of less disturbed and unmetamorphosed ‘Proterozoic’ platformal sediment package lying over deformed and metamorphosed Archean to Paleoproterozoic basement in several parts of Peninsular India is informally termed as ‘Purana’ basins in Indian stratigraphy. The trend shift in the understanding of these basin fills in last two decades, often supported by international collaborations, has made significant advancements in respect to unconformity and ‘Sequence’ development, relationship with accretion and break-up of the supercontinents, initiation and evolution of the basins in different tectonic set ups, nature of sediment provenance, paleoclimate and paleo-weathering patterns and basin water chemistry. Geophysical backups encompassing the basins, occasionally extending up to the craton and adjacent mobile belts helped in refining the understanding on the basement structure and tectonic forcings. The present paper is an attempt towards the collation of the database generated in last two decades in order to present the status of current understanding on different ‘Purana’ basins with regard to interactions of physical, chemical and biological parameters of the Proterozoic Earth.

Southern part of Rajasthan, well known for lamprophyre intrusives associated with Ajabgarh supracrustals of South Delhi Fold Belt (SDFB) and alkaline complexes. They display a new assemblage of lamprophyres with Neoproterozoic Erinpura granites near Andor in Sirohi district. These lamprophyres have shown anomalous uranium contents (upto 0.116% U3O8) along the highly ferruginised and fractured contact zones with Erinpura granites. Petrochemically, they show ultrabasic basanitic composition and sodi-potassic nature similar to alkaline lamprophyres (AL) and can be classified as ‘camptonite’. However, radioactive lamprophyres have significantly low CaO content (~1.4%). They also show significant enrichment of Cu, Ni, Zn, V and Y as compared to non-radioactive lamprophyre. The associated peraluminous high-K calc-alkaline pink granites exhibit features similar to highly evolved S-type granites as evidenced by their highly fractionated and differentiated (DI: 80–91) nature. The Rb–Sr whole-rock isochron data of Andor lamprophyres have yielded an age of 740±64 Ma with initial 87Sr/86Sr ratio of 0.7071±0.0018. These mafic dykes show close spatial and temporal association with felsic magmatism i.e., Erinpura granite plutons of Sirohi and adjoining areas (c. ~740 Ma) and can be inferred that they are coeval to Erinpura granites and probably emplaced during the waning stage of Neoproterozoic tectonomagmatic cycle of SDFB.
Presence of discrete uranium minerals (pitchblende and davidite) together with ilmenite and anatase mostly associated with ferruginous matter along the microfractures account for the uraniferous anomalies in lamprophyres, whereas resistate minerals viz., monazite, thorite, zircon and fine opaques associated with fluorite mainly control the radioactive phases in granites. A pronounced and progressive enrichment of uranium has been indicated in both, lamprophyres and granites, where post-magmatic events such as hydrothermal activity and alteration phenomenon leading to epigenetic vein type uranium mineralisation. Hence, widespread prevalence of lamprophyres in Sirohi district viz., Isra, Danwa, Pipela, not only confirms alkaline magmatism but also makes them potential targets for exploration considering their close spatial association either with CU-Zn-Au or U mineralisation.

The Tethyan Metallogenic Belt (TMB), extending from Europe through Anatolia to Iran, is one of the world's major metal producing belts, and consists of many sectors. Mineral deposits of the Biga Peninsula in northwestern Turkey exhibit, in many ways, the characteristics of mineral deposits found throughout the belt. Biga Peninsula tectonically forms the westernmost part of the Sakarya Zone and easternmost part of the Rhodope Zone at the intersection of Gondwana and Laurasia. The Biga Peninsula metallogeny research and exploration project created a GIS inventory of mineral deposits and prospects, and classified them genetically to evaluate the mineral deposit potential using genetic models based on descriptive data. The GIS database, consisting of 128 deposits or prospects, helped to generate new prospects and potential prospects. This field-based study indicated that the Biga Peninsula forms a prime target for gold-copper exploration not only in Turkey but in the world. The current economically significant mineral deposits of the Biga Peninsula were shaped by Cenozoic calcalkaline magmatism, ranging between 52 and 18 Ma, and related to mainly collisional and post-collisional tectonic regime. Epithermal Au-Ag deposits including high-(HS), low-(LS) and intermediate-sulfidation (IS) styles, porphyry Au-Cu-Mo and base-metal skarn systems are economically the most important. Though there are no currently economic examples of some of them in the Biga Peninsula, other deposit types include Carlin-like distal disseminated Au-Ag, orogenic Au, especially listwanite hosted, volcanogenic Mn and U, lateritic (ferricrete) Fe deposits, carbonate replacement (CR) and placers. Several active metal mines, such as Balya, Arapucandere and Koru, are operating in the Biga Peninsula.

The supracrustal rocks of the Older Metamorphic Group (OMG), consisting of metasediments and ortho-amphibolite, constitute the oldest unit in the Archaean nucleus of Singhbhum. However, there are indications that still older (3.4-3.8 Ga) crust of both sialic and mafic composition existed in this region. The OMG ortho-amphibolites were formed by partial melting of mantle with near chondritic composition ca. 3.3 Ga ago, probably as a result of plume activity. Shortly afterwards, partial melting of the underplated mafic material produced a tonalitic melt (Older Metamorphic Tonalitic Gneiss -OMTG), which intruded the OMG supracrustals and the entire suite was deformed and metamorphosed to upper amphibolite facies. Subsequent to this, melting of the OMG ortho-amphibolites and the lower crustal material of probable andesitic composition produced melts varying in composition from tonalite to granite and these intruded in different phases to produce plutons of Singhbhum Granite, Bonai Granite and Kaptipada Granite, which together form volumetrically the major part of the Archaean nucleus. The older OMG and OMTG occur as enclaves within these younger granitoids. The time difference between the emplacements of the OMTG and the early phases of younger granitic intrusion was of the order of 100-200 Ma. Thus, serial additions of juvenile material led to the formation of a stable microcontinent by 3.2 Ga. Thermally triggered stretching in this microcontinent produced basins peripheral to the present day Singhbhum Granite pluton, and in these basins the younger supracrustal rocks of the Iron Ore Group (IOG), consisting of BIF, associated argillaceous and subordinate arenaceous rocks, and mafic lavas were laid down. There is inadequate field or geochronological evidence to resolve the issue of whether the different iron ore basins were coeval or not. Meagre geochronological data suggest that some of the BIFs are older than ca. 3.1 Ga. Post-IOG activity is confined to the intrusion of mafic dyke swarms and formation of intracratonic basins, the ages of both being uncertain.

Evaluation of individual soil horizons and sequences of soil horizons in archaeological studies is critical to the correct and meaningful interpretation of archaeological context. We focus on the evaluation of soils in the stratigraphic framework of an archaeological site and offer a guide to assist in the interpretation of context of cultural materials in specific master horizons. In the North American Stratigraphic Code, the formal pedostratigraphic unit, the geosol, by definition requires being overlain by a formally defined lithostratigraphic  or similar material unit. This criterion can rarely be met in shallow, mid-to-late Holocene settings. In addition, no subdivision of the geosol are recognized, a problem at the scale of archaeological excavation. Chronostratigraphic and pedostratigraphic units are often confused in concept. The main distinction between these two, critical to archaeology, is in their boundaries and in the subdivision into smaller units. Boundaries of chronostratigraphic units are synchronous and form isochrons, whereas boundaries of pedostratigraphic units are time-transgressive. Subdivision of chronostratigraphic units results in subunits that represent shorter periods of time than the larger unit and that lie in temporal succession with each other (i.e., they follow the Law of Superposition). When a pedostratigraphic unit is subdivided, logically into soil horizons, the individual horizons are not separate from the whole soil, or from each other in temporal framework. Each soil horizon has a unique set of properties and processes, and is separated in space, but not in time from adjacent horizons. The distinction between subdivision of chronostratigraphic and pedostratigraphic units is a fundamental difference between soil and sediments. The guide we present is based on pedogenic and geomorphic processes, both past and contemporaneous, occurring in specific master horizons.

Gatecliff Shelter provides a deeply stratified record of humaneenvironment interaction in the Desert
West spanning most of the middle and late Holocene. The well-preserved 10 m-deep deposits serve as an
important reference sequence for technological and subsistence change in the Great Basin. Archaeological
work started at Gatecliff in 1970 and a geochronological framework was established based on 47
uncalibrated radiocarbon (14C) dates obtained from several conventional radiometric laboratories between
1972 and 1982. These radiocarbon dates are not well accommodated within a Bayesian chronological
model for these important deposits due to multiple temporal reversals and large analytical errors.
This model was discarded in favor of one based on a combination of high-precision AMS 14C dates of
short-lived carbonized plant remains supplemented with existing 14C dates culled from the original set
using a Bayesian chronological model. Summed probabilities of the modeled posterior distributions of
these 14C dates (N ¼ 24) show episodic use of the shelter as a logistic hunting camp between 6050 and
3315 cal BP, a significant hiatus in occupation between 3315 and 2145 cal BP, and more persistent use by
family bands after this time. In the future, this high-precision chronology will provide the foundation for
reinterpreting broader patterns of technological and subsistence change in the Intermountain West and
evaluating these changes relative to high-resolution climate records

The Cevizlidere deposit, located in the Tunceli Province of eastern Anatolia, is the largest porphyry Cu-Au-Mo system in Turkey. The deposit is spatially related to a composite stock, which was emplaced into Paleozoic limestones and Paleogene andesitic rocks to the southeast of the Munzur mountains, near the southwestern margin of the Ovacık pull-apart basin. The host plutonic rocks at Cevizlidere are porphyritic, medium-K calc-alkaline diorites and granodiorites. 40 Ar/ 39 Ar incremental step-heating analysis of two igneous biotite separates obtained from syn-mineral diorite porphyry yielded late Oligocene cooling ages of 25.49 ±0.10 and 25.10±0.14 Ma, whereas hydrothermal biotite yielded an age of 24.73±0.08 Ma. Re-Os ages obtained from two molybdenite separates (24.90±0.10 and 24.78±0.10 Ma) indicate that porphyry-style alteration and mineralization developed shortly after magma emplacement. The whole-rock geochemical composition of the Cevizlidere porphyry intrusions is consistent with derivation from partial melting of the metasomatized supra-subduction zone mantle. However, based on regional tectonic reconstructions, Oligocene magmatic activity in this area appears to be related to a major kinematic reorganization that took place at around 25 Ma, during the switch from subduction to collisional tectonics in eastern Anatolia. This kinematic switch may be attributed to break-off of the Southern Neo-Tethys oceanic slab prior to the Arabia-Eurasia continent-continent collision (~12-10 Ma) following widespread middle Eocene (50-43 Ma) arc/backarc magmatism. In this respect, the subduction-related tectonic setting of the late Oligocene Cevizlidere porphyry deposit is similar to that of the middle Eocene Çöpler epithermal Au deposit. The late timing of Cevizlidere with respect to the Southern Neo-Tethys subduction may be comparable to some early to late Miocene porphyry-epithermal systems that lie within the contiguous Urumieh-Dokhtar belt in central Iran. The later timing in Iran reflects the diachronous nature of the Eurasia-Afro-Arabia collision.

'Matthew D. Eddy succeeds in making a significant contribution to [the] recent and more nuanced approach to post-Kuhnian history of science… Students of eighteenth-century Scottish culture and medicine will find much of value here, as will students of eighteenth-century geology and chemistry.’  -- Arthur Donovan, American Historical Review

Summary
Classification is an important part of environmental science, yet the specific methods used to construct Enlightenment systems of natural history have proven to be the bête noir of studies of eighteenth-century culture. One reason that systematic classification has received so little attention is that natural history was an extremely diverse subject which appealed to a wide range of practitioners, including wealthy patrons, professionals, and educators. In order to show how the classification practices of a defined institutional setting enabled naturalists to create systems of natural history, this book focuses on developments at Edinburgh's medical school, one of Europe's leading medical programs. In particular, it uses the career of the influential naturalist Rev Dr John Walker, the school's professor of natural history, to reconstruct the cultural and scientific basis of early environmental science.

Walker was a traveller, cleric, author and advisor to extremely powerful aristocratic and government patrons, as well as teacher to hundreds of students, some of whom would go on to become influential industrialists, scientists, physicians and politicians. This book explains how Walker used his networks of patrons and early training in chemistry to become an eighteenth-century naturalist. Walker's mineralogy was based firmly in chemistry, an approach common in Edinburgh's medical school, but a connection that has been generally overlooked in the history of British geology. By explicitly connecting eighteenth-century geology to the chemistry being taught in medical settings, this book offers a dynamic new interpretation of the nascent earth sciences as they were practiced in Enlightenment Britain. Because of Walker's influence on his many students, the book also provides a unique insight into how many of Britain's leading Regency and Victorian intellectuals were taught to think about the composition and structure of the material world.

Rutile is the most common naturally occurring titanium dioxide polymorph and is widely distributed as an accessory mineral in metamorphic rocks ranging from greenschist to eclogite and granulite facies but is also present in igneous rocks, mantle xenoliths, lunar rocks and meteorites. It is one of the most stable heavy minerals in the sedimentary cycle, widespread both in ancient and modern clastic sediments. Rutile has a wide range of applications in earth sciences. It is a major host mineral for Nb, Ta and other high field strength elements, which are widely used as a monitor of geochemical processes in the Earth's crust and mantle. Great interest has focused recently on rutile geochemistry because rutile varies not only by bulk composition reflected, for instance, in its Cr and Nb contents but also by the temperature of crystallisation, expressed in the Zr content incorporated into the rutile lattice during crystallisation. Rutile geochemistry and Zr-in-rutile thermometry yield diagnostic data on the lithology and metamorphic facies of sediment source areas even in highly modified sandstones that may have lost significant amounts of provenance information. Rutile may therefore serve as a key mineral in sediment provenance analysis in the future, similar to zircon, which has been widely applied in recent decades. Importantly, rutile from high-grade metamorphic rocks can contain sufficient uranium to allow U-Pb geochronology and (U-Th)/He thermochronology. Furthermore, in situ Lu-Hf isotope analysis of rutile permits insights into the evolution of the Earth's crust and mantle. Besides that, rutile is also of great economic importance because it is one of the favoured natural minerals used in the manufacture of white titanium dioxide pigment, which is a major constituent in various products of our daily life. Heavy mineral sands containing a significant percentage of rutile are therefore the focus of exploration worldwide. This paper aims to provide an overview of the applications of rutile in earth sciences, based on a review of data published in recent years. After giving a summary of various rutile-bearing lithologies, the focus lies on rutile geochemistry, Zr-in-rutile thermometry, O isotope analysis, U-Pb geochronology, (U-Th)/He thermochronology and Lu-Hf isotope analysis. A final outline of the economic importance of rutile highlights the demand for further rutile-related research in earth sciences.

The Bastar Craton of Central India has a thick sequence of volcano–sedimentary rocks preserved in Kotri– Dongargarh belt that developed on a tonalite-trondhjemite-granodiorite (TTG) basement followed upwards by the Amgaon, Bengpal, Bailadila, and Nandgaon Groups of rocks. Here, we report the U-Pb geochronology and Lu-Hf isotope systematics and whole rock geochemistry of volcanic rocks and associated granitoids belonging to the Pitepani basalts, Bijli rhyolites, and Dongargarh granite in the Nandgaon Group of the Kotri belt. The volcanic rocks of the Nandgaon Group are bimodal in nature in which the basalts exhibit intergranular, porphyritic to spherulitic texture composed of pyroxenes, plagioclase, tremolite, actinolite, and chlorite ± Fe oxides. The rhy-olites display porphyritic texture consisting of K-feldspar, quartz, and plagioclase as phenocrysts. The associated porphyritic granitoids have K-feldspar, microcline, plagioclase, and biotite phenocrysts within a groundmass of similar composition. The bimodal suite displays LILE, LREE enrichment, and HFSE depletion with significant negative Nb-Ta anomalies combined with slightly fractionated REE patterns in the basalts and highly fractionated patterns and prominent negative Eu anomalies in the rhyolites endorsing their generation in an island-arc/ back-arc tectonic setting. The geochemical features of the associated granitoids indicate that these are potassic and classify as within-plate A-type granites. Zircons from the basalts show clear oscillatory zoning in their CL images. They cluster as a coherent group with 207 Pb/ 206 Pb spot ages ranging from 2446 to 2522 Ma and weighted mean age of 2471 ± 7 Ma. Zircons from the rhyolite samples are subhedral to euhedral and show simple oscilla-tory zoning with some heterogeneous fractured domains. The data from two samples define upper intercept ages of 2479 ± 13 Ma and 2463 ± 14 Ma. Zircon grains in the granite show clear oscillatory zoning and their U-Pb data define an upper intercept age of 2506 ± 50 Ma. The Lu-Hf isotopic data on the zircons from the basalts show initial 176 Hf/ 177 Hf ratios from 0.280925 to 0.281018. Their ε Hf (t) values are in the range of −10.0 to −6.7. The Hf-depleted model ages (T DM) are between 3038 Ma and 3171 Ma, and Hf crustal model ages (T DM C) vary from 3387–3589 Ma. The zircons from the rhyolites show initial 176 Hf/ 177 Hf ratios from 0.280919 to 0.281020 and from 0.281000 to 0.281103, respectively, with ε Hf (t) values varying from −10 to −6.4 and from −7.5 to − 3.9. Among these, one sample shows T DM between 3038 Ma and 3182 Ma, and T DM C varies from 3377 to 3596 Ma, whereas the other sample shows ages of 2925 Ma and 3072 Ma with T DM C varying from 3208 to 3432 Ma. The initial 176 Hf/ 177 Hf ratios of the granites range from 0.280937 to 0.281062 with ε Hf (t) values of − 8.8 to −4.3. The T DM shows a range of 2979 Ma and 3170 Ma, and T DM C varies from 3269 to 3541 Ma. The predominant negative ε Hf (t) values of zircons from these rocks suggest that the source material was evolved from the Paleoarchean crust. The geological, geochemical, and geochronological evidence suggests coeval tectonic and magmatic episodes of volcanic and plutonic activity in an island-arc setting where the arc migrated toward the continental margin and played a significant role in the Neoarchean–Paleoproterozoic crustal growth of the Kotri belt of Central India.

Porphyry copper deposits (PCDs) in Iran are dominantly distributed in Arasbaran (NW Iran), the middle segment of the Urumieh-Dokhtar Magmatic Arc (UDMA), and Kerman (central SE Iran), with minor occurrences in eastern Iran and the Makran arc. This paper provides a temporal-spatial and geodynamic framework of the Iranian porphyry Cu (Mo-Au) systems, based on geochronologic data obtained from zircon U-Pb and molybdenite Re-Os dating of host porphyritic rocks and molybdenites in 15 major PCDs. The dating results define a long metallogenic duration (39-6 Ma), and suggest a long history of tectonic evolution from the accretionary orogeny related to early Cenozoic closure of the Neo-Tethys Ocean to subsequent collisional orogeny for the Iranian porphyry copper systems.

The landscapes and archaeological sites of the southern North Sea, drowned in the period 12-6 ky BP, represent an almost unexplored field of research. Published palaeoenvironmental reconstructions are largely speculative, being based on few published sea-level index points and in the absence of detailed physical and chronological surveys. In this paper, we review the postglacial geochronology for the southern North Sea, which includes 54 radiocarbon ages derived from peat, 17 from molluscs and one known dated artefact. The lack of detailed contextual information for many dated samples means that there remains uncertainty in some elevation data, and thus in the resulting interpreted sea level. The archaeological artefacts are mostly derived deposits and thus are of limited use in palaeoenvironmental reconstruction. Overall, the data are consistent with current models of relative sea-level change back to about 10 ky BP (,45 m depth) but beyond this, there is very little published data. Much more detailed stratigraphic, microfossil and geochemical analysis is needed to help verify chronological data, help interpret the sedimentary settings in which fossils and artefacts are found, and contribute towards more reliable palaeoenvironmental and archaeological reconstructions of the history of the southern North Sea.

Le camp minier de Matagami, situé dans le nord de la ceinture archéenne de roches vertes de l’Abitibi au Québec, abrite 19 gisements de sulfures massifs volcanogènes (SMV) connus dont dix ont été exploités depuis 1963. Ces gisements sont de type bimodal-mafique puisqu’associés à des niveaux de roches volcaniques felsiques dans une séquence dominée par les laves mafiques sous-marines. Malgré la richesse minérale de la région, les roches ont été peu étudiées d’un point de vue volcanologique. Pourtant, la taille, la teneur, la forme et la position des gisements de SMV sont contrôlées en partie par l’architecture volcanique. Ailleurs en Abitibi et dans le monde, le lien spatial entre la position des centres éruptifs des unités volcaniques, les conduits hydrothermaux, les failles synvolcaniques et les gisements a été établi, mais ce genre de travaux n’a jamais été réalisé dans le cas de Matagami. Plus largement, la géologie régionale de Matagami n’a pas été mise à jour depuis les années 1980.
Au niveau de la géologie régionale, les travaux réalisés avec le MRN définissent deux grands domaines (« Nord » et « Sud ») séparés par une zone de cisaillement ENE. Le Domaine Nord montre des évidences de compression D2 orientée N-S. Le Domaine Sud est affecté par une compression faible à modérée D2, mais est principalement caractérisé par des plis P1 orientés N-E. La superposition des déformations D1 et D2 crée une géométrie de « dôme et bassin » dans la Plaine Centrale, ce qui a des implications importantes pour l’exploration. Le Domaine Sud contient les secteurs suivants : le Flanc Nord, le Flanc Sud, le Camp Ouest et la Plaine Centrale. La majorité des gisements découverts à Matagami se situent sur le Flanc Sud et le Flanc Nord, alors que les deux autres secteurs représentent des zones intéressantes pour l’exploration régionale.
La séquence stratigraphique régionale contient trois groupes : le Groupe du lac Watson à la base, suivi du Groupe de Wabassee, puis du Groupe de Daniel. Le Groupe du lac Watson (~2726 Ma) contient principalement des laves felsiques tholéiitiques, surmontées par un niveau repère, la Tuffite Clé. Le Groupe de Wabassee (2726-2725 Ma) est principalement composé de laves mafiques à intermédiaires, avec localement des unités felsiques, d’affinité tholéiitique à transitionnelle. Finalement, le Groupe de Daniel (2723 Ma), nouvellement proposé et présent seulement dans la Plaine Centrale, est caractérisé par des roches volcaniques mafiques à felsiques d’affinité transitionnelle à calco-alcaline. La mise en carte de ce dernier groupe montre une géométrie de dômes et bassins dans la Plaine Centrale, avec des pendages faibles. Ces âges correspondent à l’assemblage de Deloro (2730-2724 Ma, Ayer et al., 2002). La datation par méthode U-Pb sur zircons d’une rhyolite de type Watson sous le gisement Caber dans le Camp Ouest permet de la corréler avec la Rhyolite du lac Watson du Flanc Sud, ce qui indique – avec la géochimie – que le même niveau stratigraphique favorable, celui de la Tuffite Clé, est présent également dans le Camp Ouest.
Des travaux plus détaillés ont eu lieu sur le Flanc Sud afin d’en reconstruire l’architecture volcanique. En termes méthodologiques, la géochimie des éléments majeurs et en traces a d’abord servi à la caractérisation des unités présentes, permettant ainsi la création d’une colonne stratigraphique complète. Une fois les unités identifiées, leurs variations de faciès ont été observées au sein de 19 forages et de quelques affleurements. Finalement, afin de contraindre temporellement la mise en place des unités, quatre unités felsiques du Flanc Sud ont été datées par la méthode U-Pb sur zircons.
Sur le Flanc Sud, ces travaux ont montré que deux unités effusives mafiques à intermédiaires importantes étaient présentes dans le Groupe de Wabassee, soit l’Andésite Inférieure et le Basalte Supérieur. La connaissance précise de la stratigraphie du Flanc Sud a permis de corréler des niveaux exhalatifs (« tuffites »), augmentant le potentiel économique de certains secteurs. Par ailleurs, la Rhyolite de Dumagami dans le centre du Flanc Sud a été divisée en deux: la Dacite de Dumagami-O surmontée par la Rhyolite de Dumagami-O.
Les travaux de volcanologie ont montré que les unités volcaniques felsiques du Flanc Sud se mettent en place selon le modèle de coulée de lave de type lobes-hyaloclastite. Dans le cas de la Rhyolite de Bracemac, il s’agirait d’une seule coulée, mais le cas de la Rhyolite du lac Watson, plusieurs coulées sont juxtaposées et superposées, ce qui explique son grand volume total. Le modèle de coulées de type lobes-hyaloclastite implique une présence plus importante de roches fragmentaires qu’au préalablement supposé, principalement au sommet et en bordure des coulées, ce qui a des implications pour la mise en place des gisements de SMV par remplacement sous le fond marin, notamment à Bracemac-McLeod. Finalement, la géochronologie montre que la durée du volcanisme sur le Flanc Sud est de l’ordre 5 Ma au maximum, et que les gisements se sont mis en place à l’intérieur de 2,5 Ma (probablement moins).
Ces différentes approches ont permis la création d’un modèle présentant la reconstruction volcanologique, métallogénique et géochronologique du Flanc Sud, où les principales étapes sont (1) la mise en place de la Rhyolite du lac Watson à partir de plusieurs centres effusifs; (2) la déposition de la Tuffite Clé et la mise en place de plusieurs lentilles de sulfures massifs; (3) la mise en place de la Rhyolite de Bracemac et de la Rhyolite de Dumagami-P; (4) la mise en place de l’Andésite Inférieure et de la Rhyolite/Dacite de Dumagami-O; et (5) la mise en place du Basalte Supérieur et des dernières minéralisations.
Les travaux ont également permis d’établir le lien entre la volcanologie et la minéralisation sur le Flanc Sud. Trois modèles sont proposés pour les SMV: (1) un modèle classique de mise en place de monticules de sulfures sur le fond marin, applicable aux gisements de Mattagami Lake, Orchan Ouest, Orchan, Bell Allard et Isle Dieu; (2) un modèle de lentilles tabulaires, témoins de la circulation de fluides au sein des roches fragmentaires (remplacement sous le fond marin), applicable aux gisements de Bracemac et de McLeod; (3) un modèle de remplacement le long de failles synvolcaniques, créant des lentilles discordantes, applicable aux gisements de Persévérance. Ainsi, au sein d’un même camp minier, plusieurs modèles de formation de lentilles de sulfures peuvent être considérés, selon les faciès volcaniques retrouvés dans la séquence.
Finalement, à un niveau plus régional, les travaux de géochimie ont permis de proposer un modèle pétrogénétique et tectonique suivant la théorie actualiste. Les roches de la région de Matagami se seraient tout d’abord formées en contexte d’arrière-arc océanique (groupes du lac Watson et de Wabassee). Au cours du temps, un changement de pendage dans la plaque subductée aurait fait s’approcher l’arc (Groupe de Daniel).

The Çöpler epithermal Au deposit and related subeconomic porphyry Cu-Au deposit is hosted by the middle Eocene Çöpler-Kabataş magmatic complex in central eastern Anatolia. The intrusive rocks of the complex were emplaced into Late Paleozoic-Mesozoic metamorphosed sedimentary basement rocks near the northeastern margin of the Tauride-Anatolide Block. Igneous biotite from two samples of the magmatic complex yielded 40 Ar/ 39 Ar plateau ages of 43.75±0.26 Ma and 44.19±0.23, whereas igneous hornblende from a third sample yielded a plateau age of 44.13 ± 0.38. These ages closely overlap with 40 Ar/ 39 Ar ages of hydrothermal sericite (44.44±0.28 Ma) and biotite (43.84±0.26 Ma), and Re-Os ages from two molybdenite samples (44.6±0.2 and 43.9±0.2 Ma) suggesting a short-lived (<1 my) magmatic and hydrothermal history at Çöpler. No suitable minerals were found that could be used to date the epithermal system, but it is inferred to be close in age to the precursor porphyry system. The Çöpler-Kabataş intrusive rocks show I-type calc-alkaline affinities. Their normalized trace element patterns show enrichments in large ion lithophile and light rare earth elements and relative depletions in middle and heavy rare earth elements, resembling magmas generated in convergent margins. However, given its distance from the coeval Eocene Maden-Helete volcanic arc, the complex is interpreted to be formed in a back-arc setting, in response to Paleocene slab roll-back and upper-plate extension. The tectonomagmatic environment of porphyry-epithermal mineralization at Çöpler is comparable to some other isolated back-arc porphyry systems such as Bajo de la Alumbrera (Argentina) or Bingham Canyon (USA).

The emergent salt domes of the United Arab Emirates (UAE) have been investigated in detail and examples from central Oman have been studied for comparison. The salt domes contain exotic clasts of igneous, sedimentary and low-grade metamorphic rocks of the Arabian basement that have been brought to the surface from depths of over 8 km. The clasts thus provide an opportunity to examine the lithology, geochemical composition and age of the "basement" underlying this part of eastern Arabia, where no other outcrops are available for direct study. Five volcanic rocks give consistent latest Ediacaran U-Pb zircon crystallisation dates of ca. 560-545 Ma, with Neoproterozoic, Palaeoproterozoic and Neoarchaean ages of inherited zircons. These rocks, although strongly altered, preserve geochemical characteristics compatible with formation in a within-plate, extensional setting along the northern edge of Gondwana, adjacent to Prototethys. U-Pb analyses of detrital zircons in sedimentary and low-grade metamorphic rocks indicate deposition younger than ca. 597 Ma in UAE and <734 Ma in Oman. The two UAE sedimentary rocks may correlate with the Shuram and Khufai Formations of the Nafun Group (Huqf Supergroup) in Oman. Like the volcanic rocks, the two sedimentary samples from the UAE show derivation from the erosion of Neo-, Palaeoproterozoic and Neoarchaean sources. These sources could be from the Arabian basement itself or from other basement blocks such as those embedded in present-day Iran and Afghanistan, the precise whereabouts of which in Neoproterozoic times remains somewhat uncertain. The zircon age spectra of samples from the UAE show Neoproterozoic age peak characteristics of sources from both the western and eastern Arabian basement blocks, indicating that the two segments were juxtaposed by about 597 Ma, the maximum age of their deposition.

The internal = northern zones of the Maghrebide belt includes allochthonous massifs that define, together with those from the Betics, Sicily and Calabria, a disrupted 'Alkapeca' terrane. In the Rif transect, taking advantage of new thermobarometric and geochronologic studies, we recognize a metamorphic complex with a mostly non-Alpine upper plate (Dorsale, Ghomarides-Malaguides), and a lower plate (Sebtides-Alpujarrides) affected by HP-LT, then HT-LP Alpine metamorphism. Some eastern Rif allochthons (Temsamane area) display MP metamorphism and could represent either Sebtide inliers or slivers from the African paleomargin. The Sebtide-Alpujarride late HT event also affects the bottom of the Ghomaride-Malaguide complex and can be related to the onset of the Alboran Sea rifting at ∼25-22 Ma, whereas their HP event is ascribed to an earlier (∼30-25 Ma?), north-to northeast-dipping subduction event. A review of the Algerian literature allows us to infer a similar structure and evolution for the Kabylides. The Alkapeca disruption is classically explained by back-arc extension above the retreating subduction of the Ligurian-Maghrebian oceanic lithosphere. The question of whether the latter subduction followed an earlier and opposite Alpine-Betic (Nevado-Filabride) subduction or not, remains open to discussion. To cite this article: A. Michard et al., C. R. Geoscience 338 (2006).