Paleoproterozoic Granitoids From Central Segment Of North China Craton: Geochemistry, Geochronology And Tectonic Significance

The PaleoProterozoic granitoids are generally classified into six types as adakitic granitoids,sanukitiods, Closepet type granitoids, Nb-enriched gabbros (NEG), Biotite-bearing granites and stronglyperaluminous granites in the central segment of North China craton (CSNCR). The adakitic granitoids andsanukitoids are occrenced northern and southern region along the Guyang-Wuchuan fault;sanukitoids andClosepet-type granites are occreenced middle region between Guyang-Wuchuan fault and Daqingshanmountain front fault;and strongly peralumious (SP) granitoids are mainly occenced south region alongJining-Liangcheng-Helingeer-Helanshan Mountain. Furthermore, they are usually company with themetamorphic intermedial-basic volcanic rocks as basalts and andesites, sometimes dacites. The some ofmetamorphic volcanic rocks are chemically characterized by relatively high MgO content and transitionmetals element (such Cr and Ni), and depleted in high field strength element (HFSE). They are like adkites,Nb-reriched basalts (NEB, 7 20×10-6) and magnesian andesites(MA, MgO≈6%).Adakites are generally suggested producing slab melt in the early collision. Geochemical modellingshows that the source of adakites cannot be ultramafic but rather basaltic in composition. This implies thatadakitic magmas are produced by melting of a basaltic source transformed into garnet-bearing amphiboliteor eclogite such that garnet±hornblende could be residual phases. In Daqingshan area, the high-pressuregranulite may be the residual phases. Sanukitoids genesis model was proposed that an adakitic melt risingthrough peridotite is able to assimilate olivine, resulting in a "hybridised slab melt". Which increased speedMg#, Cr and Ni in melt. Closepet-type granite is commonly late-to post-kinematic and generally associatesthe matter of crustal, which increased K and other LILE. And the Nb-enriched gabbros (NEGs) aresuggested that intruded on low crustal from the melt of peridotite hybridesed adakitic melt. Biotite-bearinggranites (BBG) are mostly anatectic granites, monzogranites and syenogranite are A-type granite.According to SHRIMP and TIMS, we have attained lots of ages for different kinds granitoids in NCR:adakitic granitoid is 2435±16Ma;sanukitoids are 2426±41Ma;Closepet granites are 2416~2330Ma;andNEG is 1845±16Ma. The SP granites are 1904 to 1933 Ma in south, but that is 2231Ma to 2438Ma in thenorth. And, the BBG and A-type granite are two stages (2277-1953Ma and 1853~1803Ma). However,Wanghuichun et al. (unpublished data) has obtained U-Pb zircon SHRIMP age for Wulashan amphibolitesuggested as middle to new Archean in past literature from the southwest of Guyang that are1953~1967Ma.Base on the geochemistry, petrology and geochronology of the Paleoproterozoic granitoids, wesuggested that subduction bearing an analogy to modern plate has taken on the Paleoproterozoic in NCR.We suggested it has two orogenic episodes, which are ~2.3Ga and ~1.9Ga. And adakitic granitoids/adkties,sanukitoids/HMA, closepet-type granites and other granites are producted with the process of subduction –collision – orogeny – uplift – extension. After studying the magma rock assemblage, we suggested thecraton time is started in ~2.3Ga, and finished in ~1.9Ga. Lüliang movement (~1.9Ga) is very importantorogenics in CSNCR, which orogenic movement time (2.3~1.9Ga) and post-orogenic cracking time(1.84~1.74) are similar to the converging and cracking time of Columbia suppercontinent. It is significantlyto studying the crustal evolution, the characteristics of Lüliang movement and paleoproterozoic Columbiasuppercontinent.