莫来铁尖晶岩的发现和玄武岩浆的深部分异作用

THE DISCOVERY OF MULLIHERCYNITITE AND DEEP-SEATED DIFFERENTIATION OF BASALTIC MAGMA

莫来铁尖晶岩是首次发现的一种新型火山岩,由铁尖晶石、莫来石、铁板钛矿和火山玻璃组成,其平均化学成分相当于一个简化的SiO_2-FeO~*—Al_2O_3三元系。莫来铁尖晶岩浆是原始岩浆深部分异的结果。原始玄武岩浆在地幔深处分离结晶出富含硬玉分子的斜方辉石、单斜辉石,进化岩浆向富Al、Fe而贫Si的方向演化,最终产生莫来铁尖晶岩浆。后者喷出地表,冷凝结晶形成莫来铁尖晶岩。

The mullihercynitite is a new type of volcanic rock discovered for the firsttime, composed of hercynite,mullite, pseudobrookite and volcanic glass. Its chemi-cal composition (%) is given as follows: SiO_2 35. 32, TiO_2 3.99, Al_2O_3 32.25, Fe_2O_319. 90, FeO 6. 20, MnO 0.17, MgO 0.39, CaO 0.05, Na_2O 0.74, K_2O 0.09, P_2O_5 0.16,H_2O^+ 0.98 and H_2O^-0.03, correspondine to. that of a simplified SiO_2-FeO-Al_2O_3ternary system. Mulliher-cynitite magma results from deep-seated differentiationof primary basaltic magma, from which orthopyroxene rich in jadeite and clino-pyroxene are removed in the deep levels of the mantle. The magma evolves towardthat rich in Al and Fe and poor in Si and finally mullihercynitite magma isproduced. The mullihercynitite magma is erupted on the surface and crystallizesto produce mullihercynitite.