Urban Geology in London No. 9 - UCLucfbrxs/Homepage/walks/Regents... · 2016-08-15 · Urban...

UrbanGeologyinLondonNo.9

©Ruth Siddall 2013, revised August 2016 2

BuildingStonesatRegent’sPlace:AnUrbanGeologyWalkAtthetimeofwriting,theRegent’sPlacedevelopmentisnearingcompletionwiththeofficeblocksintheNorthEastQuadrant(NEQ)almostreadyfortheirnewoccupiersandnewpavinglaidonHampsteadRoadandonDrummondStreet.ThesiteisownedbyBritishLandandoccupies13acresandcomprisesoffices,restaurantsandbarsaswellasresidentialbuildingsandsocialspaces.Thedeveloperspridethemselvesontheiruseofnaturalmaterialsandanumberofstonesareusedhere.Thisguideintroducesthegeologyofthemainstonesusedinthesite.Regent’sPlaceisbestaccessedfromWarrenStreetStation.CrossovertheroadtowardsthenorthandturnleftatRegent’sTowerfollowingthebuildingroundintoRegent’sPlacePlazawherethisgeologicaltourwillstart.

Regent’sPlacePlazaAninnovativeseriesofseating,inspiredbytheGiant’sCausewayinNorthernIrelandoccupiesthePlaza.Itisbuiltfromblocksofgraniteofvariableheightwhichhavebeenhollowedoutandsetonasteelframe.ThegraniteusedfortheCausewaycomesfromcentralSpainintheremoteandsparselypopulatedprovinceofExtremadura.StoneextractionisoneofthemostimportantindustriesinExtremaduraandinfactSpainisthetopEuropeanproducerofgranite,withtheprovincesofExtremaduraandGaliciabeingthemainsuppliers.AtleastfortyvarietiesarequarriedinExtremadurafroma250kmlongmassifofgraniticrockscalledtheCentralExtremaduraBatholithwhichwasintrudedintometasedimentaryrocksbetween400-500millionyears(Ma)ago.Evidenceofthemetasediments,‘schists’,canbeseeninthegraniteblocksasblackstreaksandblobs.Thesefeaturesareknownas‘xenoliths’,literally‘strangerocks’whichbecomeincorporatedintothemoltengraniteasitrisesthroughtheEarth’scrust.Theserocksshowtheclassicmineralogyofgranites;quartz,feldsparandmica.Themicaistheblackmineral,thefeldsparsarewhiteandthequartzisgrey.ThisparticularvarietyiscalledAzulExtremadureandcomesfromquarriesnearthevillageofSalvatierradeSantiagonearthetownofCaceres.TheintrusioniscalledtheZarzadeMontánchezGranodiorite.ThestonecontractorsforthisprojectandformanyotherstructuresinthelandscapingofRegent’sPlacewereBBSGraniteConcepts.



TheGiant’sCausewayseatingblocksandacloseupofAzulExtremaduregraniteshowingasmallxenolithofblackschist.Thefieldofview(FOV)is5cm.Thesculpturehousedintheconcreteblockonstiltsinfrontof2TritonSquare(SantanderBank)isbyEdwardHodgesBaily(1788-1867).ThereliefdepictstheLordNelsonacceptingthesurrenderoftheSpanishAdmiralDonFranciscoXavierWinthuysenafterhisdefeatattheBattleofStVincentin1797.Thereliefiscarvedfromwhitemarble.Theelevatedpositionofthescenemakesidentificationdifficult(andwhitemarblesarenotoriouslydifficulttoidentifybyeye)butthisisprobablycarvedfromCarrarastatuarymarble.Continueonto2TritonSquare,behindthesculpture.2-3TritonSquareBuiltin2002byarchitectsShepherdRobson,2-3TritonSquareiscladintheblackstoneNeroAssolutoZimbabwe.ThestonewassuppliedbyGormleyGroup.OntheelevationofthebuildingontheEustonRoaditisspectacularlyusedtocladtheellipticaltowers.NeroAssolutoZimbabweiswellnamedbeingabsolutelyblack,buttakingahighpolish.ItisamediumtocoarsegraineddoleritebelongingtoasuiteofigneousintrusionsknownastheMashonalandSillComplex.At1.87billionyears(1870millionyears)old,thisisbyfartheoldestrockencounteredatRegent’sPlace.



NeroAbsoluteZimbabweontheellipticaltowersalongtheEustonRoadsideof2-3TritonSquare.Therearemanysills(sheet-likeigneousintrusions)outcroppinginwesternZimbabweintheregiontothewestandsouth-westofthecapitalHarare.Doleritesaretypicallydarkor‘mafic’incolourbeingdominatedbythemajorrockformingmineralpyroxene.Inthisexample,largequantitiesoftheblackironoxidemagnetiteaddtodeepenthecolour.Plagioclasefeldsparisalsopresent.Walkaroundthebuildingandtrytofindashadycornerwherethereisnotmuchreflectedlighttoexaminetherockwithahandlens,thegrainsizeis2-3mm.NeroZimbabwewasfirstmarketedcommerciallyintheearly1970sandcontinuestobeapopularstoneandamajorexportofZimbabwetothepresentday.1,4&7TritonSquareThelargeblockoccupyingTritonSquarewasdesignedandbuiltbyArupAssociatesin1997.AlthoughthemainentranceonRegentsPlazaisallglassfronted,walkingroundthebuildingtowardsthewestshowsadistinctivegreygraniteatpavementlevel.Thegraniteismainlymediumgrainedbutcontainssparserectangularandsquarephenocrysts(thatiscrystalslargerthanthegroundmassoftherock)ofwhitefeldspar.ThisisBarreGreyGranitefromVermont,USA.Vermontisknownas‘TheGraniteState’andthetownofBarrewasonce‘thegranitecapitaloftheWorld’.Commercialproductionbeganin1830andBarreattractedimmigrantsfromOldWorldstoneproductionareassuchasItaly,Scotland,SpainandScandinavia.Anobserverinthelate19thCenturynoted“manyScotchmenhavecomeherefromthegraniteindustryinAberdeen,Scotland.Someoftheseexpresstheopinionthatascomparedwiththeoldcountrythemenhereworkharder,receivehigherwages,spendmoremoneyandarenohappier.”(Seager,2001).Onlyonequarryisstillinproduction,theRockofAgesQuarrynearthevillageofUpperGraniteville.TheBarreGraniteisDevonianinage,intrudedat380MaduringtheAcadianmountainbuildingeventofthenorthernAppalachians.

Left:4TritonSquare,withJulianOpie’sinstallation.Right:closeupofthegreygraniteatpavementlevel.Theupperpartofthebuildingiscladinabuffsandstone.AccordingtoArupAssociates,thisiscalled‘PierreduNod’,aMid-JurassiccalcarenitefromtheCôteD’OrregionofBurgundy.Unfortunately,ontheexternalwallsofthebuilding,thestoneisseveralmetresabovepavementlevelandnotreadilyexamined.Howeveritisironrichandtheivory-colouredstoneismottledwithrusty-brownpatchesandshows‘liesegangbanding’,aphenomenacausedbyiron-richwaterspercolatingthroughtherock.Thelightinstallation‘RuthwalkinginJeans’onthewest-facingsideoftheblockisbyJulianOpie(b.1958).Walkalongthewestsideof4TritonSquaretoLongfordSquareontheNsideofthedevelopment.



DrummondStreetandLongfordSquareGranitecladplantersandseatingblocksarelocatedonHampsteadRoadandonDrummondStreet.Thesearemadeofabeautifulblue-colouredgranitefromBrittany,NWFrance.ThequarriesatLanhelinaresituatedintheBonnemainGranitewhichliesafewkilometressouthofthetownofStMaloinBrittany.MostoftherocksofwesternFrance,knownastheArmoricanMassiftogeologists,arerelatedtoandthesameageofthoseinCornwallandSpainandwereformedduringamajormountainbuildingepisodecalledtheVariscan(orHercynian)Orogenywhichreacheditsfinalstages~300millionyearsago.HoweverintheareaaroundStMaloandtheadjacentChannelIslandsareformedofrockswhichbelongtoanoldereventknownastheCadomianOrogeny.TheBonnemaingranitehasbeendatedto527Ma(Dallmeyeretal.,1993).ThepavingonDrummondStreetisofgreyWhitworthStone.ThisisafinegrainedsandstonefromthemoorsofthePenninesbetweenLancashireandWestYorkshire.ThisisoneofthestonesusedforpavingwhichbelongstothegroupknowngenericallyasYorkStone,thoughnoneofitcomesfromanywherenearYork.TheyarederivedfromthemanybedsofflagstonesfoundwithinthePennineLowerCoalMeasuresGroupofCarboniferousage.VarietiesofYorkStoneareubiquitousonthepavementsofLondon.Thisparticularvarietyisratherunusualinthatitisdovegreyincolour,withpatchesandbandsstainedpaleorangebyiron.TheoriginalsedimentswerelaiddowninmajorriversystemsflowingovertheCarboniferouscontinent.Theassociatedcoalswereformedfrompeatsandplantmaterialpreservedinswampsandstagnantwaters.EvidenceofthisisalsoseenintheWhitworthStoneflags;particlesofblackorganicmaterialareseenconcentratedalongfossilripplesandothersedimentarystructures

Left:LongfordSquare.TheplanteronthefarleftisBlueLanhelinGranitewithpavingofpalegreyWhitworthStone.Right:Whitworthstoneshowingblackflecksoforganicmatterconcentratedalongfossilripples,FOV30cm.ThekerbstonesareofPortugueseAlentejoDarkGreyGranite.Thisisadensemedium-finegrainedgranitewitha‘salt&pepper’speckledeffect,fromwest-centralPortugal.ThisgraniteissimilarinageandorigintotheAzulExtremadureusedinRegent’sPlacePlaza.ReturntoTritonSquare,andturnleftandpasstheNewDioramaTheatreontoTritonStreet.20TritonStreet20TritonStreetmarksthewesternendoftheRegent’sPlacedevelopment.Thislargebuilding,byTerryFarrell&Partners,2010,housesanItalianRestaurantandofficeaccommodation.Atwo-



storeyarcaderunsaroundthebuildingfromTritonStreetontoOsnaburghStreetsupportedbypillarscladinredstones.Atpavementlevel,thefoundationsareofaredgranite.ThisisVångaGranitefromnearKristianstadinsouthernSweden.Thisisanancientstone,over1.4billionyearsold.LikethegranitesinRegent’sPlaze,itcontainsthedefiningmineralsquartz,feldsparandmica.Here,thefeldsparisrichinpotassiumandadeeporange-redcolour.Themica,thevarietybiotite,isblackandonceagainthegreymineralisquartz.TheVångaGranitewaspartofagroupofgranitesknownastheKarlshammSuitewhichwereintrudedintotheBlekingeandSkånegeologicalterranesofsouthernSweden.Forthemostparttheseintrusionshowtypicalgranitetextureswithrandomlyorientatedcrystals,butthewesternmostVångagranitewasdeformed;itwasintrudednexttoabeltofdeformationandasaconsequencewecanseethatthefeldsparshavebeenstretchedandalignedtoformastrongfoliation.Thebiotitehasalsobeenconcentratedtogetherinstreak-likefeaturescalled’schlieren’.

Left:20TritonSquare,theredgraniteisatpavementlevel.Right:closeupofthegranite,FOV5cm.Thewellcolour-matchedstonecladdingtheupperpartsofthepillarsandtherestofthebuildingisabovemostpeople’shead-heightonTritonStreet,butslightlylowerandeasiertoobserveonOsnaburghStreet.Fromadistancethestoneslookverysimilarbuttheupperstoneisnotagranitebutasandstone.ItisfromWüstenzellinCentralGermany,avillagesituatedmidwaybetweenthecitiesofFrankfurtandNuremberg.WüstenzellerStoneisTriassicinage,around250millionyearsold.ItcomesfromanextensiveseriesofsandstonescalledinGermanBuntsandstein.‘Bunt’meanscolouredorvariegatedandcoloursvaryfromredthroughbuffandyellowtogreen.HowevermostareredandWüstenzellerStonecomesfromaunitcalledtheRoterMainsandsteinwhichformstheuppermostpartofthesuccession.TheBuntsandsteinsorBunterBedsastheirEnglishequivalentswereknown,filledanaridcontinentalbasin–adesert–whichstretchedfromEnglandacrosscentralEurope.Strikinginthisstonearetheflecksofthewhitemica,muscovite,whichreflectthesunandsparkleonthesurface.Othermineralspresentarequartzandfeldspar(thesesandstonesrepresenterodedremainsofgranitesandthereforehavethesamemineralogy)andtheredcolourisimpartedbyironoxides.Notablyabsentfromthesesandstonesareclayminerals.Claysrequirewatertoformfromthechemicalweatheringofmicaandfeldspar,andtheirabsenceinthesesandstonesindicatesanextremelyaridclimateatthetimeoftheirdeposition.Thestonefor20TritonStreetwassuppliedbyGermancontractorsHofmannNaturstein.10TritonStreetoppositeiscladwithasyntheticmaterial,reconstitutedlimestone,intendedtoimitatePortlandStone.



ThepavingonbothsidesOsnaburghStreetappearsidenticaltoBritishYorkStone.However,despitethereassuringly‘northern’-soundingname,thisstoneisnotfromtheBritishPennines.Theoriginofthestoneisunknown.ItisprobablethatitisfromIndia.FluvialflagstonescropoutandareextensivelyquarriedintheregionofBundiinsoutheasternRajasthan,whichdespitebeingProterozoicinage,areindistinguishablefromYorkStone,butconsiderablycheaper!Flagstonesandsettsareusedtocreatepavements.Regent’sPlacePavillionBetween10and20TritonStreetisanartinstallationandseatingarea,theRegent’sPlacePavillionbyKevinCarmody(b.1975)andAndrewGroarke(b.1972).

Left:Regent’sPlacePavillion.Right:thegreengabbrousedontheseating.ThePavillionfeaturessmallpavingsettsandblockseatingofstone.Thisisadark,grey-greengabbroicrockwithfuzzy,equigranularcrystals.Thediffusemarginsofthecrystalssuggestthattherockisslightlyalteredandmineralsarebeginningtobreakdowntoformclays.Howeverthemainmineralogyisapalegrey-greenplagioclasefeldsparplusadarkbrownpyroxeneorhornblende.Onceagaintheoriginofthisstoneisunknownanditcouldhavebeenderivedfrommanysources.Thisistheendofthiswalk.Turnleft(south)alongOsnaburghStreetwhichleadsbackontoEustonRoadandGreatPortlandStreetUndergroundStation.

SourcesandFurtherReading

AshfieldGroup:www.ashfieldgroup.com

Castro,A.,1985.TheCentralExtremadurabatholith:geotectonicimplications(EuropeanHercynianBelt)-anoutline.,Tectonophysics,120,57-68.

Dallmeyer,R.D.,Brown,M.,D’Lemos,R.S.&Strachan,R.A.,1993,VariableVariscanthermalrejuvenationintheStMaloregion,CadomianOrogen,France:evidencefrom40Ar/39Armineralages.,JournalofMetamorphicPetrology.,11,137-154.

GormleyGroup:2-3TritonSquare:http://www.gormley.co.uk/

HoffmanNaturalStone:http://www.hofmann-naturstein.com/files/download_regents_place.pdf

Lott,G.,2012,Strategicstonestudy:abuildingstoneatlasofWest&SouthYorkhire.,EnglishHeritage.,25.http://www.bgs.ac.uk/mineralsuk/mines/stones/EH_atlases.html

Price,M.T.,2007,DecorativeStone:TheCompleteSourcebook.ThamesandHudson,p.235.



Regent’sPlaceArtGuide.BritishLand.http://www.regentsplace.com

Rubio-Ordóñez,A.,Valverde-Vaquero,P.,Corretgé,L.G.,Cuesta-Fernandez,A.,Gallastegui,G.,Fernandez-Gonzalez,M.&Gerdes,A.,2012,AnEarlyOrdoviciantonalitic–granodioriticbeltalongtheSchistose-GreywackeDomainoftheCentralIberianZone(IberianMassif,VariscanBelt).,GeologicalMagazine,149(5),927–939.

Seager,D.R.,2001,Barre,VermontGraniteWorkersandtheStruggleAgainstSilicosis,1890-1960.,LaborHistory,42(1),61-79.

Söderlund,U.,Hofmann,A.,Klausen,M.B.,Olsson,J.R.,Ernst,R.E.&Persson,P-O.,2010,TowardsacompletemagmaticbarcodefortheZimbabwecraton:baddeleyiteU–Pbdatingofregionaldoleritedykeswarmsandsillcomplexes.,PrecambrianResearch183,388–398.AcknowledgementsIwouldliketothankJasonPlant,RichardCowanandJamesDanbyatBritishLandforprovidingmewithinformationonthestonesandcontractorsusedontheirdevelopmentatRegent’sPlace.IamalsogratefultoKateHarperandPaolaBlasiofArupAssociatesforprovidingthenamesofthestonesusedtoclad1,4&7TritonSquare.©DrRuthSiddall,UniversityCollegeLondon,GowerStreet,LondonWC1E6BT,UK:[email protected]

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Urban Geology in London No. 9 - UCLucfbrxs/Homepage/walks/Regents... · 2016-08-15 · Urban...

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