CAJ | 학술논문

东江口花岗岩体位于商丹与勉略缝合带之间的南秦岭中部,其中存在大量基性暗色微粒包体.锆石的LA-MCICPMS联机U-Pb年代学分析表明,东江口岩体的形成年龄为223Ma,其包体锆石的结晶年龄为222Ma,与寄主岩体大致同时形成,指示秦岭造山带印支晚期岩石圈构造体制属性从挤压.伸展转变发生在220Ma左右.锆石的Lu-Hf同位素原位分析结果表明,南秦岭晚三叠纪花岗岩是壳幔混合作用的产物,亏损的幔源岩浆与南秦岭(或扬子)的基底地壳物质可能为南秦岭地区晚三叠纪花岗岩的源区物质,它们的形成起因于秦岭造山带在主造山期后发生的岩石圈拆沉作用.大约220Ma开始,南秦岭岩石圈构造应力性质从挤压向伸展构造体制转变,岩石圈发生拆沉作用,地幔软流圈物质上涌并底侵于下地壳,诱发下地壳物质的部分熔融,当岩浆沿构造薄弱带上升过程中,幔源岩浆与寄主岩浆发生成份的交换,两种岩浆混合过程中不完全混溶,最终形成寄主岩体和暗色基性微粒包体.
동강구화강암체위우상단여면략봉합대지간적남진령중부,기중존재대량기성암색미립포체.고석적LA-MCICPMS련궤U-Pb년대학분석표명,동강구암체적형성년령위223Ma,기포체고석적결정년령위222Ma,여기주암체대치동시형성,지시진령조산대인지만기암석권구조체제속성종제압.신전전변발생재220Ma좌우.고석적Lu-Hf동위소원위분석결과표명,남진령만삼첩기화강암시각만혼합작용적산물,우손적만원암장여남진령(혹양자)적기저지각물질가능위남진령지구만삼첩기화강암적원구물질,타문적형성기인우진령조산대재주조산기후발생적암석권탁침작용.대약220Ma개시,남진령암석권구조응력성질종제압향신전구조체제전변,암석권발생탁침작용,지만연류권물질상용병저침우하지각,유발하지각물질적부분용융,당암장연구조박약대상승과정중,만원암장여기주암장발생성빈적교환,량충암장혼합과정중불완전혼용,최종형성기주암체화암색기성미립포체.
The Dongjiangkou granitic pluton is exposed in the South Qinling terrain between the Shang-Dan and the Mian-Lue suture zones.This granitic pluton generally contains abundant mafic enclaves of different types.Results of zircon U-Pb dating for a granite and two mafic enclaves by using the LA-MC-ICPMS technique show that the Dongjiangkou granitic pluton crystallized in 223Ma and mafic enclaves formed simultaneously in 222Ma.This magmatism of early Mesozoic constrains the time of tectonic transformation from compression to extension in the Qinling orogenic belt.Hf isotopic composition of zircons obtained by the LA-MC-ICPMS technique suggests that the granitic pluton resulted from a mixing-mingling process between mantle-derived mafic magma and crustal-derived granitic magma.The mafic magma originated likely from depleted mantle,while basement rocks of the South Qinling(or Yangtze)terrain contributed major material source for the granitic pluton.This magmatic activity is attributed to lithospheric delamination during the post-orogenic stage of the Qinling orogenic belt.