中国东南部晚中生代岩浆作用的深部条件制约

通过对中国东南部区域地质条件的分析和地球物理资料的研究，获得了如下认识：1．区域构造作用和基底物质成分影响并制约着晚中生代岩浆活动，岩浆岩的分区性具有很好的地表与深部一致性；2．按岩浆岩类型可分为三区，即沿海钙碱性中酸性火山－侵入杂岩区、武夷山弱过铝花岗质火山－侵入杂岩区和赣江以西强过铝花岗岩区，三者之间分别被政和－大埔断裂与赣江断裂所分隔；3．在沿海地区，存在局部高导层，推测与拉开裂解有关。玄武岩浆底侵和碱性花岗岩形成与晚白垩世拉张作用关系密切；4．政和－大埔、赣江和长乐－南澳三大断裂是重力梯度带或梯度宿突变带，且深部地球物理存在明显差异，可能是壳幔作用剧烈的场所；5．存在中地壳低速带，厚2－4km，为地壳部分熔融或韧性变形产物，推测是部分晚中生代花岗岩浆的策源地；6．支持中国东南部晚中生代岩浆作用的板块俯冲＋陆内玄武岩浆底侵的成因模式，日本中央构造线－台湾纵谷带是中生代太平洋板块朝东亚陆缘消减的俯冲带和缝合带。

Deep Geological Conditions Constraning the Late Mesozoic Magmatism in SE China

Analyses of regional geologic settings and geophysic d ata have yielded following results: 1.The regional tecto nism and material composition of basement had influenceon the Late Mesozoic mag m a activity,and the magmatic division at the surface is consistent with that in the deep.2.Based on the types of magmatic rocks,three tectonic-magma regions are recognized: (a) low-K and high-Al calc-alkaline i ntermediate-ac id volcanic-intrusive complex region,i.e.,SE China Coastal Region; (b) hi gh-K granitic volcanic-intrusive complex region,named as the Wuyishan region and (c) high-K S-type granite region in the west to Ganjiang without acid volcan ic intrusive complex.These three regions are separated by Zhenghe-Dapu and Gan jiang fault zones respectively.The crustal thickness in the SE China Coastal Region is thinner,whose basement is mostly volcanic and granite belongs to I- type; the crustal thicknesses for other two regions are greater than the first,their basements are mostly me lted sedimentary rock series and the granitic rock is S-type.The Ganjiang fau lt zone is called as the Late Mesozoic Volcanic Rock Line.3.In the SE China Co as tal Region,there is a local-low-resistivity-layer,which was related to a pull-rifting.The undeerplating of basaltic magma and the formatio n of alkaline granit were closely related to the pull-rifting in the Late Creta ceou s.4.Zhenghe-Dapu,Ganjiang and Changle-Nan'ao fault zone have apparent geoph ys ic features,which are both the gravity gradient zones and ultra-crust fault zo nes where the geological interaction along the crust-mantle boundary is most co mmon.5.There is a low-velocity zone of 2-4km thick in the middle crust,an d is considered as a result of a part melting of ductile deformation,which is probably a local magmatic source.6.Our study supports the model of plate subd u ction combining with underplating of basalt magma for the origin of the Late Mes ozoic magmatism in the SE China.The fault zone from the Japanese Central Tecto nic Line to Taiwan Longitudinal zone is a Mesozoic subduction and suturing zone wher e the Mesozoic Pacific plate subducted to the East Asian continental margins to form a wide volcanic-intrusive arc.