【摘要】 研究表明,中酸性岩浆岩（包括 SiO₂>56%的中酸性火山岩和侵入岩）的 Sr 和 Yb 是两个非常有意义的地球化学指标,如果大致按照 Sr=400×10^-6和 Yb=2×10^-6为标志,可以划分出4类花岗岩,即:高 Sr 低 Yb(Sr>400×10^-6,Yb<2×10^-6)、低 Sr 低 Yb(Sr<400×10^-6,Yb<2×10^-6)、低 Sr 高 Yb(Sr<400×10^-6,Yb>2×10^-6)和高 Sr 高 Yb(Sr>400×10^-6,Yb>2×10^-6)型花岗岩。其中,从低 Sr 高 Yb 型中还可以分出非常低 Sr 高 Yb(Sr<100×10^-6,Yb>2×10^-6)的一类。因此,按照 Sr 和 Yb 含量的不同,可以将花岗岩分为5类,文中着重探讨了这5类花岗岩形成的源区深度问题,指出按照残留相组成和花岗岩地球化学特征,可以将花岗岩形成的压力分为3或4个级别:即:（1）高压下与石榴石平衡的花岗岩具有高 Sr 低Yb 的特征;（2）在中等或较高压力、麻粒岩相（由斜长石+石榴石+角闪石+辉石组成）条件下,花岗岩具低 Sr 低 Yb 或高 Sr 高 Yb 的特点（取决于原岩成分）;（3）低压下,残留相有斜长石无石榴石（角闪岩相）,花岗岩为低 Sr 高 Yb 类型的;（4）与蛇绿岩有关的在洋壳剖面浅部由辉长岩部分熔融形成的 M 型花岗岩,具有非常低 Sr 高 Yb 的特点,形成深度约2～5km,可能是非常低压条件下形成的。研究表明,淡色花岗岩大多分布在低 Sr 低 Yb 区,部分正长岩和钾玄岩分布在高 Sr 高 Yb 区。藏南淡色花岗岩可能形成的压力较高。文中探讨了岩浆与深度的关系,得出了一些初步的认识,指出需要进一步研究的问题。为了得到经得起考验的结论,还需要更多资料的积累,更多理论的探讨和更多实验的佐证。更多还原

【Abstract】 Intermediate-acid igneous rocks including volcanic and intrusive rocks with SiO₂>56% can be divided into four types on the basis of their Sr and Yb contents:high-Sr and low-Yb type (Sr>400×10^-6 and Yb<2×10^-6);low-Sr and Yb type (Sr<400× 10^-6 and Yb<2×10^-6),low-Sr and high-Yb type (St<400×10^-6 and Yb>2×10^-6),and high-Sr and Yb type (Sr>400×10^-6 and Yb>2×10^-6).In the low-Sr and high-Yb type,some granites can be grouped as very low-Sr and high-Yb type with Sr<100× 10^-6 and Yb>2×10^-6.It is therefore five types of granites on the basis of their Sr and Yb contents.The variation of the Sr and Yb contents of the granites are related to the depth of the magma source.With the contents of Sr and Yb and mineral assemblage of the residual magma,the pressure at which granite formed may have four ranges;（1）granites formed at high pressure with garnet left in the redisual phase,magma have high Sr and low Yb content;（2）granites formed at medium or higher pressure such as granulite facies （composed of plagioclage+garnet+amphibolite+pyroxene） have low Sr and Yb,or high Sr and Yb content,depending on the composition of protohth;（3）granites formed at low pressure with plagioclase in residual phase （amphibohte facies） have low Sr and high Yb contents,and（4）M-type granites related to ophiolite formed by partial melting of gabbro at shallower depth （2 to 5km） have very low Sr and Yb content.In general,most lecuogranites are of low-Sr and Yb type,whereas some syenite and shoshonite are high- Sr and high-Yh type.The lecuogranites in southern Tiebet may have formed at relatively high pressure.It is discussed in this study that the relationship between the composition of magma and formation depth,which is a preliminary work and need more evidence to approve.更多还原