The Liaodong Peninsula,in the northeastern part of the Eastern Block in the North China Craton,China, consists of lithologic units from Archean to Cenozoic in age.The basement rocks consist of widespread amphibolite-to granulite-facies Archean supracrustal assemblages and granitoid gneisses,as well as Paleoproterozoic volcano-sedimentary successions that were intruded by granitic-marie complexes,and then metamorphosed under greenschist-to amphibolite-facies conditions.The basement rocks are overlainby thick Mesoproterozoic- Cenozoic sedimentary sequences.A synthesis of the available petrological and geochronological data allowed us to establish a geological framework for the Precambrian basement on the Liaodong Peninsula and its vicinity.The basement can be subdivided into three tectonic units:the Neoarchean Liaonan Block,the Eo-Neoarchean Longgang Block,and the intervening Paleoproterozoic Jiao-Liao-Ji Belt.In this paper we delineate the characteristics of an Archean tectonothermal event,and in a companion paper we examine the Paleoproterozoic lithotectonic assemblages.Rock samples of the Hadean eon are rare worldwide,but Hadean zircons have been identified in rocks of the Liaodong Peninsula,and they provide one of the oldest known mineralogical records on Earth.The Archean gneisses in the Liaonan Block are dominated by quartz dioritic-granodioritic gneisses that were emplaced between 2.55 and 2.44 Ga,and these rocks later underwent a lower-amphibolite-facies metamorphism.On the other hand,the Archean basement in the Longgang Block is dominated by TTG (tonalitic-trondhjemitic-granodioritic) and granitic gneisses,chamocldtes,and small amounts of supracrustal sequences with much older protolith ages of up to 3.85 Ga,and these rocks have undergone amphibolite-to granulite-facies metamorphism.Posttectonic magrnatism (ca.2.5 Ga)marked the end of the Archean tectonothermal event in the Eastern Block of the North China Craton.
Mafic rocks are widespread on the Liaodong Peninsula and adjacent regions of the North China Craton.The majority of this magmatism was originally thought to have occurred during the Pre-Sinian,although the precise geochronological framework of this magmatism was unclear.Here,we present the results of more than 60 U-Pb analyses of samples performed over the past decade,with the aim of determining the spatial and temporal distribution of mafic magmatism in this area.These data indicate that Paleoproterozoic-Mesoproterozoic mafic rocks are not as widely distributed as previously thought.The combined geochronological data enabled the subdivision of the mafic magmatism into six episodes that occurred during the middle Paleoproterozoic,the late Paleoproterozoic,the Mesoproterozoic,the Late Triassic,the Middle Jurassic,and the Early Cretaceous.The middle Paleoproterozoic(2.1-2.2 Ga)mafic rocks formed in a subduction-related setting and were subsequently metamorphosed during a ca.1.9 Ga arc-continent collision event.The late Paleoproterozoic(ca.1.87-1.82 Ga)bimodal igneous rocks mark the end of a Paleoproterozoic tectonothermal event,whereas Mesoproterozoic mafic dike swarms record global-scale Mesoproterozoic rifting associated with the final breakup of the Columbia supercontinent.The Late Triassic mafic magmatism is part of a Late Triassic magmatic belt that was generated by post-collisional extension.The Middle Jurassic mafic dikes formed in a compressive tectonic setting,and the Early Cretaceous bimodal igneous rocks formed in an extensional setting similar to a back-arc basin.These latter two periods of magmatism were possibly related to subduction of the Paleo-Pacific plate.
