Late Caledonian magmagenesis in Southern Scotland

The Priestlaw and Cockburn Law intrusions are zoned granitoid plutons intruded into Lower Palaeozoic sediments at the margin of, and prior to closure of, the Iapetus Ocean. They vary from marginal basic rocks to more acid rocks towards their centres. The parental magmas to the plutons were derived from an isotopically depleted mantle modified by melts/fluids during subduction. Zonation in the plutons was caused by combined assimilation and fractional crystallisation (AFC), and rates of assimilation were low relative to rates of fractionation. A series of pyroxene-mica diorites in Priestlaw are however hybrids formed by simple mixing. Porphyrite-acid porphyrite dykes, associated with the plutons, represent chilled portions of the pluton magmas; more evolved quartz porphyry dykes represent crustal melts. Lamprophyre dykes have high LILE and LREE abundances and relative depletions of HFS elements, typical of subduction related ultra-potassic magmas. High Mg numbers, Ni and Cr contents and experimental constraints, imply near primary status for the least evolved lamprophyres. Their enrichments in incompatible elements, high La/Nb, La/Yb, Sr and low Nd indicate derivation from a previously metasomatised mantle source. Granitoid plutons and lavas in the northern Southern Uplands have high Nd and low Sr, whereas the younger plutons of the southern Southern Uplands have higher Sr, La/Yb and lower Nd, consistent with derivation from a more enriched source. No plutons however have remained as closed systems. Three magmatic suites are present in southern Scotland: (1) Midland Valley Suite (2) Northern Southern Uplands Suite and (3) Southern Southern Uplands Suite, consistent with previous models indicating northward underthrusting of English lithosphere below the southern Southern Uplands. Further underthrusting of decoupled lithospheric mantle is indicated by the presence of lamorophyres in the eastern Southern Uplands, and took place between 410 Ma and 400 Ma.

Geoquímica de elementos maiores e traços de granitoides neoproterozoicos da província Borborema e sua correlação com propriedades físicas de rochas

This paper discusses the correlation of thermal conductivity, density and magnetic susceptibility with composition of major and trace elements of Neoproterozoic igneous bodies from Borborema Province, Northeastern Brazil. These properties were used as potential markers among the studied magmatic suites. For the correlation between petrophysical and geochemical properties it was considered a set of 195 chemical analyzes of granitoid rocks, separated by the degree of acidity in basic, intermediate and acidic. Major (SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O and TiO2) and some trace elements (Rb, Sr, Ba, Zr, Th and U) that are usually linked to the formation of the most common minerals of igneous rocks were used. The results show that SiO2 has the best positive correlation with the thermal conductivity, while Al2O3, CaO, Fe2O3, MgO and TiO2 exhibit negative correlation for the same property. The correlation with density is opposite to that one for these oxides with the thermal conductivity. The magnetic susceptibility did not correlate with the elements studied. The results for thermal conductivity and density indicate a tendency of SiO2 and oxides with higher affinity with mafic minerals (Al2O3, CaO, Fe2O3, TiO2 and MgO) in controlling these petrophysical parameters. The set of samples was divided into five different magmatic suites based on their lithogeochemical aspects into: i) peralkaline / alkaline; ii) alkaline; iii) calc-alkaline; iv) high potassium calcium alkaline; and v) shoshonitic. Data analysis showed that the thermal conductivity and density presented good results in the individualization of these suites, notably between peralkaline / alkaline, alkaline suites, calc-alkaline and shoshonitic. However, the high-K calc-alkaline suite overlapped with the other. In contrast, the magnetic susceptibility did not show effective results for separating the five chemical suites.

Geochemistry for sediment core MD02-2496

Variations in chalcophile and redox-sensitive trace elements are examined at high-resolution intervals from a ~50 kyr long sediment core (MD02-2496) from the Vancouver Island margin. Enrichments of Ag, Cd, Re, U, and Mo above lithogenous levels, signifying sedimentary suboxia and anoxia, occurred during the early Holocene and Bølling/Allerød, and during warm interstadial events of Marine Isotope Stage (MIS) 3. Down-core trace element profiles co-vary with productivity proxy records (opal, CaCO3, and marine organic carbon), and with sedimentary nitrogen isotope ratios, which reflect variably enriched nitrate upwelled from intermediate waters that were transported northward from the Eastern Tropical North Pacific. The similarity of the MD02-2496 record with records from the southern portion of the California Current System (CCS), and to the Greenland ice core oxygen isotope record during warm climate intervals, suggests that sedimentary redox conditions along the California Current responded to local productivity, to North Atlantic climate change and to tropical Pacific surface water processes via long-distance teleconnections. Concentrations of trace elements and productivity proxies were relatively depleted during the Younger Dryas, cool stadial events of MIS 3, and in two episodes of glaciomarine sedimentation from ~14.7 to 30.5 kyr BP (last glacial maximum, LGM), and from 44 to 50.4 kyr BP. Cordilleran Ice Sheet advancement onto the Vancouver Island continental shelf during the LGM led to intervals of increased terrigenous sedimentation and greatly reduced productivity not seen in the southern portion of the CCS, and along with ventilation of North Pacific Intermediate Waters, resulted in brief sedimentary oxic conditions.

Source Provenance of Pre-Historic Granitic Grindstones: The Case Study of the Cogotas I Archaeological Site of Arroyo Mucientes/San Lázaro (Castronuño, Valladolid) and a Proposal on the General Methodological Flow Process

The occurrence of hand grindstones at the Cogotas I archaeological sites is considered to be a common feature. Given that a distant-provenance raw material is frequently involved, determination of its source is a basic factor in the search for a better understanding of resource management and for any Political Economy approach. To progress in these directions an overall study should be planned, using selected grindstones with a view to covering diverse sub-zones of the Cogotas I dispersal area, especially because of its considerable distance from the granite basement source. Such a study may today includes diverse analytical procedures combining successive geographic, petrographic, mineralogical and geochemical criteria. To check the plausibility of the proposed methodology, a preliminary test has been carried out on two granite grindstones, obtained at the archaeological excavation at the Castronuño (Valladolid) Cogotian site, which is fifty km away from an inferred source area that was presumably located at Peñausende (Zamora). The result obtained validates the proposed operational process, yielding a generalizable knowledge to other similar situations.

Plutonismo granítico varisco no Centro Norte de Portugal

O complexo batolítico das Beiras está localizado na Zona Centro Ibérica (ZCI), no centro norte de Portugal. É predominantemente composto por rochas granitóides instaladas em metassedimentos de idade Neoproterozóica - Câmbrica Inferior, Ordovícica e Carbonífera Superior, durante ou após a última fase de deformação dúctil varisca (D3). No seu conjunto, as rochas granitóides do Batólito das Beiras cobrem um amplo espectro de idades (sin-, tardi- e tardi-pós-D3) e tipologias (tipo S e transicionais I-S). Neste trabalho apresentam-se dados petrográficos, mineralógicos, geoquímicos e isotópicos para estas intrusões e discutem-se os principais processos envolvidos na sua génese.

Tracing the Cambro-Ordovician ferrosilicic to calc-alkaline magmatic

U–Pb geochronological study of zircons from nodular granites and Qtz-diorites comprising part of Variscan high- grade metamorphic complexes in Gredos massif (Spanish Central System batholith) points out the significant presence of Cambro-Ordovician protoliths among the Variscan migmatitic rocks that host the Late Carboniferous intrusive granitoids. Indeed, the studied zone was affected by two contrasted tectono-magmatic episodes, Car- boniferous (Variscan) and Cambro-Ordovician. Three main characteristics denote a close relation between the Cambro-Ordovician protholiths of the Prado de las Pozas high-grade metamorphic complex, strongly reworked during the Variscan Orogeny, and other Cambro-Ordovician igneous domains in the Central Iberian Zone of the Iberian Massif: (1) geochemical features show the ferrosilicic signature of nodular granites. They plot very close to the average analysis of themetavolcanic rocks of the Ollo de Sapo formation (Iberia). Qtz-diorites present typical calc-alkaline signatures and are geochemically similar to intermediate cordilleran granitoids. (2) Both Qtz-diorite and nodular granite samples yield a significant population of Cambro-Ordovician ages, ranging between 483 and 473 Ma and between 487 and 457 Ma, respectively. Besides, (3) the abundance of zircon inher- itance observed on nodular granites matches the significant component of inheritance reported on Cambro- Ordovician metagranites and metavolcanic rocks of central and NW Iberia. The spatial and temporal coincidence of both peraluminous and intermediate granitoids, and specifically in nodular granites and Qtz-diorite enclaves of the Prado de las Pozas high-grade complex, is conducive to a common petrogenetic context for the formation of both magmatic types. Tectonic and geochemical characteristics describe the activity of a Cambro-Ordovician arc-back-arc tectonic set- ting associated with the subduction of the Iapetus–Tornquist Ocean and the birth of the Rheic Ocean. The exten- sional setting is favorable for the generation, emplacement, and fast rise of subduction-related cold diapirs, supported by the presence of typical calc-alkaline cordilleran granitoids contemporary with ferrosilicic volcanism.