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Malaya Formation     

Lithology

Sandstone, conglomerate, with minor dacitic tuff, ignimbrite

Stratigraphic relations

Not reported

Distribution

Cervantes Basin, Benguet

Age

Pleistocene

Thickness    

1,200 m

Named by

Maleterre (1989)

The Malaya Formation was defined by Maleterre (1989) and Ringenbach (1992) for the thick clastic and volcaniclastic sequence that constitutes the infill of the Cervantes Basin with type locality along Malaya River, west of Cervantes.  The bulk of the basin fill consists mainly of light-colored, poorly indurated sandstones and conglomerates associated with minor dacitic tuff and ignimbrites.  Most of the clasts are andesites, and clasts represented by the substratum (metavolcanics, diorites) are rare.  An upper member confined around the Malaya River area is made up of 200 m of poorly indurated red sandstone, claystone and polymictic conglomerates.  The clasts in the conglomerates include andesites, metavolcanics and diorites.  Slope breccias along the Abra River fault south of Malaya intertongue with the clastic and volcaniclastic rocks.  The total thickness for this formation was estimated by Maleterre (1989) at 1,200 m.

This formation could be coeval with the MankayanDacitic Complex in Mankayan, Benguet, especially the upper member (Batodaciticpyroclastics), since the Malaya Formation is intercalated with dacitic tuff and ignimbrites.

A Late Miocene to Pliocene age was earlier assigned to the Malaya Formation (Maleterre, 1989).  Later studies, however, indicate that the age is younger than was supposed, since field data point to a post-mineralization deposition.  Previously, mineralization was thought to have occurred at around 2.9 Ma (Sillitoe and Angeles, 1985).  More recent data indicate that mineralization took place between 1.45 and 1.2 Ma (Arribas and other, 1994).  Laser probe dating (40Ar/39Ar) of hornblende from an ignimbrite bed in the Malaya Formation gives a best age estimate of 0.9 ± 0.2 Ma.  Therefore, a Pleistocene age is adopted for the Malaya Formation.

Formation sequenceEdit

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