'Ata Island, Tongatapu, Tongai

Regional Level Types
'Ata Island	Island
Tongatapu	Administrative Region
Tonga	Country

A volcanic island in the far south of the Tonga archipelago.

It consists of a small remnant (1.8 km²) of a large composite volcano which had at least four main centres of eruption.

The lavas are mainly porphyritic basaltic andesites, with minor phenocryst - poor basalts, and are dominated by phenocrysts of calcic plagioclase.

Clinopyroxene, mainly augite, is also a significant phenocryst phase and orthopyroxene, olivine and microphenocrysts of titaniferous magnetite occur in small amounts.

The groundmass textures are intergranular and hyalo-ophitic and consist of plagioclase, augite, pigeonite, titaniferous magnetite, cristobalite, devitrification products after glass, brown glass, and two coexisting glasses which represent immiscible silicate liquids.

Zeolite and hematite are rare secondary minerals.

Analyses of the coexisting glasses show that they are very similar to coexisting glasses found in lunar basalts.

Some very interesting blocks of medium- and coarse-grained, mafic to silicic rocks and some small andesite pumice blocks occur in a block breccia.

The basalts and basaltic andesites have a very restricted range of compositions (50-55% SiO2) with a pumice block sample being the most siliceous (62.25% SiO2).

Chemically the rocks are similar to rocks from the other Tonga Islands and are more similar to those from the Kermadec Islands.

Fossils

This region is too big to display the fossil list, try looking at smaller subregions.

References

Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/%CA%BBAta
Wikidata ID:	Q423507