摘要
根据岩石地球化学特征 ,可以将华北克拉通北缘的中生代花岗岩类划分为钙碱性和高钾钙碱性花岗岩、强过铝质淡色花岗岩、高锶花岗岩、碱质 A型花岗岩和碱性花岗岩五个类型。强过铝质淡色花岗岩起源于泥砂质变沉积岩在地壳加厚和隆升过程中的减压脱水熔融 ;高锶花岗岩起源于强烈加厚陆壳的下部或壳幔过渡带的中酸性或基性岩石脱水部分熔融 ;碱质 A型花岗岩和碱性花岗岩均为岩石圈伸展背景下的岩浆作用产物 ,但后者明确指示区域岩石圈已处于板内裂谷状态。在区域地质演化总体框架下 ,中生代各类型花岗质岩浆活动的时间序列 ,明确反映出区域地球动力学背景从碰撞后到非造山的演化过程 :钙碱性和高钾钙碱性花岗岩 +强过铝质淡色花岗岩 +高锶花岗岩 +碱质 A型花岗岩构成碰撞后花岗岩套 ,而碱性花岗岩 +碱质 A型花岗岩则构成板内非造山花岗岩套。区域花岗岩浆活动的演化表明 ,华北克拉通北缘地区中生代重大构造转折应发生在 160～ 150 Ma之间。在 160 Ma以前的中生代早中期 ,区域岩石圈仍处于碰撞后前期的强烈加厚的过程之中 ,该时期以出现大量的高锶花岗岩和少量过铝质淡色花岗岩为特征 ;150～ 110 Ma期间为碰撞后晚期的区域岩石圈强烈伸展时期 ,该时期则以高锶花岗岩侵位事件的急剧减少和碱质 A型花岗岩大量?
Based on petrological and geochemical studies, the Mesozoic granitoids out cropped in the northern marginal region of North China Craton can be grouped into five types as following: strongly peraluminous leucogranites, normal calcalkaline and high-K calc-alkaline granites, high-Sr granites, alkali A-type granites, and peralkaline granites. They are very different not only in their geochemical features, but also in age of emplacement, petrogenesis and geodynamic environment. The peraluminous leucogranites were derived from dehydration melting of metapelites and metagreywackes during uplift and decompression of the thickened crusts without any mantle involvement in the early stage of post-collisional phase. The high-Sr granites were derived from the overthickened lower crust by dehydration melting of intermediate-acid igneous rocks and basaltic amphibolites. Both alkali granites and peralkaline granites were generated in the extensional regime of regional lithosphere, but the latter indicating a rifting event of intra-plate anorogenic setting. Based on the regional geological evolution and the sequential emplacement of the granitoids, it is suggested that these granitoids imagined a transition of geodynamic environments from post-collisional to intra-plate anorogenic. The strongly peraluminous leucogranites + calcalkaline and high-K calc-alkaline granites + high-Sr granites + alkali A-type granites comprise the post-collisional granitic suite, while the peralkaline granites + alkali A-type granites constitute the intra-plate anorogenic granitic suite. The regional. granitic magmatism distinctively indicates a significant switch of regional tectonics in between 160similar to150 Ma in the Mesozoic. In the early-middle Mesozoic before 160 Ma, regional crust/lithosphere might undergo an early stage of post-collisional thickening processes, during which voluminous high-Sr granites and several strongly peraluminous leucogranites were emplaced; but during 150similar to110 Ma, the regional crust/lithosphere experienced a late post-collisional stage of strongly extensional tectonics and crustal thinning, which is characterized by the onset of emplacement of alkali A-type granites, along with the high-Sr granites became markedly insignificant and eventually disappeared. At about 110 Ma typical pealkaline granites were emplaced without any high-Sr granitic magmatism, indicating that the regional crust had been thinned to normal thickness (38similar to40 km) and intra-plate rifting began. It is believed that the 'subduction-style' geochemical signatures of the post-collisional calc-alkaline and high-K calc-alkaline granites were inherited from the source regions that had been activated during the subduction and syn-collision stages of the Siberian plate subducting beneath the North China Craton.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2002年第4期433-448,共16页
Acta Petrologica Sinica
基金
中国科学院资源环境领域知识创新工程重大项目 ( KZCX1 - 0 7)资助
关键词
中生代
花岗岩
侵位事件
岩石圈
granitoids
mesozoic
post-collisional
anorogenic
North China Craton
