Bedrock thumb|300px|Reconstruction of the Old Red Continent against which the terranes or "building blocks" of the Sudetes collided in Late Paleozoic times. The area of present-day Sudetes lies near the eastern end of Avalonia. The igneous and metamorphic rocks of the Sudetes originated during the Variscan orogeny and its aftermath. The Sudetes are the northeasternmost accessible part of Variscan orogen as in the North European Plain the orogen is buried beneath sediments. Plate tectonic movements during the Variscan orogeny assembled together four major and two to three lesser tectonostratigraphic terranes. The assemblage of the terranes ought to have involved the closure of at least two ocean basins containing oceanic crust and marine sediments. This is reflected in the ophiolites, MORB-basalts, blueschists and eclogites that occur in-between terranes. Various terranes of the Sudetes are likely extensions of the Armorican terrane while other terranes may be the fringes of the ancient Baltica continent. One possibility for the amalgamation of terranes in the Sudetes is that the Góry Sowie-Kłodzko terrane collided with the Orlica-Śnieżnik terrane causing the closure of a small oceanic basin. This event led to obduction of the Central Sudetic ophiolite in the Devonian period. In the Early Carboniferous the joint Góry Sowie-Kłodzko-Orlica-Śnieżnik terrane collided with the Brunovistulian terrane. This last terrane was part of the Old Red Continent and could correspond either to Baltica or the eastern tip of the narrow Avalonia terrane. Also by the Early Carboniferous the Saxothuringian terrane collided with the Góry Sowie-Kłodzko-Orlica-Śnieżnik terrane closing the Rheic Ocean.
bEDrOck Thumb|300Px|reCoNstRucTiOn of The old RED contInent aGainsT which the terRanes or "buiLdinG bLoCkS" of ThE SudeteS cOllided In LAte paLeOzoic TIMeS. thE AReA of preSENt-day suDeTEs Lies near thE EasteRn End Of avAloniA. thE iGneous And mEtamOrphiC rOckS of tHE suDEteS ORiginaTed durinG THe varIscan oRogeNY anD itS AFtermath. the sudetEs are tHe NoRtheASteRnmost accESSIbLE pArt of Variscan OROgEN AS In the NOrTh eurOpean plaIN The orogEn is bURieD BenEAth sedimenTS. pLate TEctoniC MOVemenTS dURiNg thE varIScAn oroGEnY asSembled TOgetheR FOUr MajoR and two to THreE lEssEr tectOnostratigRaphIc teRRanes. THE asseMBlage OF The teRrAnES ought tO HaVe inVolvEd The clOsure Of At LEast tWo OcEAn basIns coNtAiNiNg OCeanic CrUst AND mariNe sEdImEnts. tHis iS ReflEctEd iN ThE opHioLiTeS, mOrB-BasAlts, bLUEsCHists And eClogiteS That oCCur in-bETween TERranES. variOus teRranes of ThE SUDetes are liKeLy extEnsionS of the aRMorIcan teRraNe WHiLE otHer terRaNes mAy Be thE FriNges of The AnCiEnT bAltiCA continent. ONe pOssibIliTy for tHE amaLgamation oF TErranes in tHe suDeteS is thaT The góRy sOwIE-kłodzKo teRrane collidEd with the orLicA-śnieŻnIK tERRane caUsiNg the Closure OF a SmalL oceanIc basIn. ThIS Event lEd To obdUCTion oF tHE cENTrAl sudEtiC opHiOLite IN thE dEvoNIAn period. In the EarLy carbonIFErouS The jOInt GÓry sOwiE-KŁOdZko-OrlICA-śNieżnik TerraNe ColliDeD with the BRuNOViSTulian terrane. This laSt TerranE WaS part of thE olD ReD conTiNent aND cOuld coRrespOnd eITher To balticA oR the EasterN TIp of tHe nArrOw avAlONiA TErRaNE. aLso by thE EArLy caRBonifeRoUs The SaXOThurInGIAn tErranE cOllided wIth the GórY sowiE-kŁodzko-OrlicA-ŚniEżniK TeRranE CloSing the rheIc oceaN.