Mineralogy and geochemistry of pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain monogenetic volcanoes in the central part of the Cameroon Volcanic Line

Pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain,3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line(the Tombel Plain,Bamileke Plateau,and Noun Plain),were explored in order to constrain their petrology and make some predictions on their pozzolanicity.The rocks in this study include alkaline and subalkaline basalts,trachybasalts,and basanites.Most of these rocks present an overall composition that overlaps with primitive mantle,suggesting rapid ascent of magmas,limited crustal contamination and crystal fractionation of olivine,clinopyroxene,and feldspar.The pozzolans present enrichment of LREE relative to HREE and high chondrite normalized ratios of La/Yb and Tb/Yb.ranging between 7 and 20 and>1.9 respectively,similar to those of Ocean Island Basalts.Like other nearby volcanoes,partial melting in a dominantly garnet-bearing mantle zone can be assumed.Quantitative mineralogy by X-ray diffraction revealed various mineral phases with dominantly plagioclase,augite,olivine,and Fe-Ti oxides.The samples contains important amorphous phase up to 23,51,and 69 wt%in the Tombel Plain,Noun Plain,and Bamileke Plateau,respectively.This elevated amount of amorphous phases together with the sum of SiO2,Al2O3 and total Fe2O3(SAI=68.50-83.50>70 wt%)according to ASTM C618 standard and the sum of CaO,FeO,and MgO(CIM=14.5-30.52 wt%and 23.58-31.08 wt%)suggest interesting pozzolanicity character for the studied pozzolans.

The Discovery of Late Pleistocene Daliuchong Volcanic Conduit in th Tengchong Volcanic Field

Objective The Tengchong volcanic field is situated along the southeastern margin of the Tibetan Plateau and adjacent to the border area of western Yunnan Province of China and Myanmar.Affected by the intense tectonic stress of subduction of the Indian plate to Eurasian plate,this volcanic field has experienced strong volcanism.

Nature and evolution of the lower crust under central Spain:Inferences from granulite xenoliths(Calatrava Volcanic Field-Spanish central system)

So far,the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System(SCS).In recent years,ultramafic volcanics from the Calatrava Volcanic Field(CVF)have also provided deep-seated crustal xenoliths which have not been studied in detail.Our data,combining mineral,whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths,highlight the felsic composition of the lower crust under central Iberia.A number of the Calatrava xenoliths represents Variscan igneous protoliths,which are a minor population in the SCS,and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny(leucodiorite protolith age of 314±3 Ma and leucogranite protolith age of 308±2.5 Ma).U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas.These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue,which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions.The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana.These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component,ultimately extracted from an Eburnean crust.Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes.