Tennantville gabbroic anorthosite

Title

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)

SiO₂

52.36

52.37

TiO₂

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

Na₂O

3.69

4.02

K₂O

.90

.86

P₂O₅

.16

-

H₂O+

.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

Western Minerals Inc.

Spatial Coverage

Adirondack Highlands-collected from a low road cut on Military Road at the north edge of the Edinburg Quadrant.

Temporal Coverage

Precambrian

Accrual Method

Purchased from Western Minerals Inc.

Number of Thin Sections

1

Geolocation