华北东部中生代晚期—新生代软流圈上涌与岩石圈减薄

Asthenospheric upwelling and lithospheric thinning in late Cretaceous-Cenozoic in eastern North China.

现今的地幔是由软流圈地幔（热的，主元素饱满、微量元素亏损的，塑性流变性质的）、古老岩石圈地幔（地幔1，冷的，主元素贫瘠、微量元素富集的，刚性的，以方辉橄榄岩为代表）以及现今的岩石圈地幔（地幔2，主元素饱满、微量元素亏损，以二辉橄榄岩为代表，可能包括多时期形成的）组成。古老岩石圈地幔与地幔2样品的共存、100-4．3Ma在地幔内部持续发生的古老岩石圈与软流圈的相互作用以及上述作用的时空不均一性，都表明了岩石圈减薄是软流圈呈“蘑菇云状”大规模上涌的结果。上述事件发生于100Ma以后。软流圈来源的玄武岩大范围喷发并伴随了岩石圈的强烈拉伸是事件发生的主要标志，岩石圈减薄是一个深部地质过程，不像是突发事件。

The upper mantle beneath eastern North China contains three mantle end members, they are the asthenospheric mantle, the surviving Archaean old lithospheric mantle （1）, and the present lithospheric mantle （2）. The asthenospherie mantle is characterized by abundance in major dements, depletion in trace elements, and thermal and plastic rheological behavior. The Archaean old lithospheric mantle is represented by harzburgite, and it is relatively poor in major elements, rich in trace elements, and has a cold and rigid behavior. The lithospheric mantle （2） is represented by lherzolite, and characterized by an abundance major elements and depleted trace dements. The mantle （2） may contain mantle blocks of different ages. The coexistence of old lithospheric xenoliths and mantle （2） xenoliths in basanite from Hebi and in alkaline basalt from Fuxin demonstrates that the Archaean old lithospheric mantle had existed from 100 Ma to 4. 3 Ma beneath Fuxin and Hebi before the basanites and alkaline hasalts were erupted. The discovery of geochemical features of interaction between the old mantle and the asthenospheric mantle in mantle rocks and minerals also indicates the existence of the old mantle beneath eastern North China. The above two facts confirm the ＂mushroom model＂ of asthenosphere upwelling. The temporal and spatial heterogeneity of asthenospheric upwelling further supports the assumption that lithospherie thinning resulting from asthenosphere upwelling, instead of the large extent delamination of lower crust and old mantle The mark of lithospherie thinning is the widespread eruption of asthenosphexe-derived hasalts in eastern China accompanied by strong lithospherie extension. It started at approxirnatdy 100 Ma. In fact, such dramatic lithospheric thinning was a deep-process not a paroxysmal event.