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The Songshugou Alpine-type ultramafic massif intruded into the surrounding plagioclase-amphibole schists where high-temperature aureoles are found well exposed but not distroyed.From the outer part inwards,four aureoles are recognized:the oligoclase-hornblende zone,the andesine-hornblende zone,the garnet zone and the pyroxene zone.Toward the massif,systematic variations are noticed in the rocks from one zone to another,i.e.,the rocks varyfrom fine-grained,fibrous,crystalloblastic texture to medium coarse-grained,granular,crystalloblas-tic texture and from schistose structure to massive structure;hornblende varies from blue-green to brofn;plagioclases vary in composition from An_(12-17),to An_(37),even to An_(60)nearthe contact;garnet and pyroxene become more and more abundant;sphene is replaced pro-gressively by titanomagnetite;and Na(K),A1 and Ti in the hornblende tend to increase nearthe contact.Studies have shown that the typical rocks in the four contact metamorphic zones are ge-nerally similar in major and trace elements.But different mineral assemblages and mineralchemistry indicate that the rocks were formed under different physical conditions.
The Songshugou Alpine-type ultramafic massif intruded into the surrounding plagioclase-amphibole schists where high-temperature aureoles are found well exposed but not distroyed. From the outer part inwards, four aureoles are recognized: the oligoclase-hornblende zone, the andesine-hornblende zone , the garnet zone and the pyroxene zone. Toward the massif, the systematic variations are noticed in the rocks from one zone to another, ie, the rocks varyfrom fine-grained, fibrous, crystalloblastic texture to medium coarse-grained, granular, crystalloblas-tic texture and from schistose structure to massive structure; hornblende varies from blue-green to brofn; plagioclases vary in composition from An_ (12-17), to An_ (37), even to An_ (60) nearthe contact; garnet and pyroxene become more and more abundant; sphene is replaced pro-gressively by titanomagnetite; and Na (K), A1 and Ti in the hornblende tend to increase nearthe contact.Studies have shown that the typical rocks in the four contact metamorphic zones are ge-ne rally similar major and trace elements.But different mineral assemblages and mineralchemistry indicate that the rocks were formed under different physical conditions.