SUMMARY

Geological, petrographical and petro-geochemical characteristics of effusives in the northwest of Quảng Nam Province

Bùi Thế Vinh, Huỳnh Trung

Effusive formations distributed in the northwest of Quảng Nam Province were studied in the Project “Geological mapping and mineral survey at 1/50,000 scale of the A Hội - Phước Hảo map sheet group, Quảng Nam Province”. They form large covers of flow-form with the thickness changing in hundreds metres and are penetrated and divided into small areas by Late Paleozoic intrusives.

Almost all these effusives were altered in different levels. Their initial composition was mainly basalts (tholeiitic series) and, lesser, dacite and rhyolite (plagiorhyolite). Altered rocks consist mainly of greenschist with the chemical composition of spilite still preserving the spilite texture. More acidic rocks were altered into rocks with the chemical composition of orthophyre (or orthophyre albite) with the typical petrographical composition of porphyritic trachyrhyolite, tephrite, phonotephrite, trachydacite, …

The above effusives can be coupled into the spilite-keratophyre formation formed during the (primary) oceanic crust spreading stage together with mafic-ultramafic intrusives of the ophiolite association.

Người biên tập: Bùi Minh Tâm.