Tennantville gabbroic anorthosite

Identifier

AD-14

Description

This medium grained facies is one of a number of anorthositic sheets that intrude throughout the stratigraphic section of the southern Adirondacks. A chemical analyses of specimens from this outcrop yield results that are almost identical with Buddington's (1939) average gabbroic anorthosite.

 


Tennantville locality (McFarland)

Average Gabbroic
Anorthosite (Buddington)

SiOâ‚‚

52.36

52.37

TiOâ‚‚

1.14

-

Al₂O₃

23.75

24.68

Fe₂O₃

1.11

1.24

FeO

3.96

3.49

MnO

.07

-

MgO

1.53

2.0

CaO

10.63

10.57

Naâ‚‚O

3.69

4.02

Kâ‚‚O

.90

.86

Pâ‚‚Oâ‚…

.16

-

Hâ‚‚O+

.69

.90

Total

99.99%

100.13%

The existence of these instrusive sheets of gabbroic anorthosite argues strongly against the proposition that the anorthositic rocks constitute part of an older, pre-Grenvillian basement complex. Rocks similar to the Tennantville gabbroic anorthosite commonly occur as border facies surrounding larger, coarser bodies of anorthosite. Spongy, brick-red garnets are common in these rocks.
Thin section shows plagioclase and clinopyroxene.

Date

1980

Contributor

Temporal Coverage

Accrual Method

Purchased from Western Minerals Inc.

Number of Thin Sections

1

Geolocation