中国东部显生宙地幔演化的主要样式 :“蘑菇云”模型

THE MAIN EVOLUTION PATTERN OF PHANEROZOIC MANTLE IN THE EASTERN CHINA: THE “MUSHROOM CLOUD” MODEL

从地幔类型、地球物理资料、岩石学研究成果 3方面讨论了中国东部显生宙地幔演化的主要样式 ,认为古老岩石圈地幔物质以亏损玄武质组分的橄榄岩为主 ,岩石密度低 ,具上浮性质 ,是克拉通稳定的主要原因 ,不可能发生因重力诱发的拆沉作用。白垩纪晚期—新生代地幔成分为饱满的二辉橄榄岩 ,地温高 ,明显有别于古老地幔。该热地幔物质呈“蘑菇云”状上涌 ,蘑菇云之间仍有古老地幔的残留体 ,二者多数呈陡边界接触 ,这是东部地幔演化的主要样式。与此同时岩石圈伸展导致岩石圈减薄。中生代中国东部绝大部分地区地温很高、地壳厚度大 ,但许多问题尚待研究。古老岩石圈地幔中的低速、低阻物质为流体和低熔程度的熔体 ,它们呈脉状、透镜状 ;新生代地幔中的该物质为含熔体的软流圈物质 ,它们呈多个蘑菇云状 ;中生代地幔中的低速物质可能为大量的玄武质熔体 ,呈蘑菇云平流层状。中生代壳幔相互作用明显 ,克拉通稳定时期及新生代时期层圈之间相互作用的活跃带位于岩石圈与软流圈之间。

According to the discrimination of three mantle domains, geophysical data and the research on petrology of mantle in Eastern China, the evolution pattern of Phanerozoic mantle is proposed in this paper The old lithospheric mantle is mainly composed of refractory low density peridotites, while the buoyancy relative to the asthenosphere and the stability of old mantle must also be taking into account Therefore the old SCLM (sub continental lithosphere mantle)can not be delaminated by gravitation processes In Late Cretaceous—Cenozoic the composition of SCLM is fertile in lherzolite that is different evidently from the old SCLM These hot mantle materials uplifted as several mushroom cloud and their boundaries with old mantle relicts were steeply inclined This is the main evolution pattern of mantle in the eastern China In Mesozoic, the geotherm of mantle was raised in most regions of the eastern China and was hotter than that of the old lithospheric mantle and than that of Cenozoic one The thickness of the crust in Mesozoic may be thicker than that in the older and Cenozoic The low velocity/low resistance materials in the old mantle were fluids and melts with low meltability occurred as veins and/or lenses Those materials in Cenozoic mantle were hot asthenospheric and presented as several mushrooms and those in Mesozoic may be abounded in basaltic magmas, as forming mushroom advective stratosphere In Mesozoic, the most important interaction occurred between the crust and the mantle, whereas in the older and Cenozoic it did between the lithosphere and the asthenosphere