3rd geo report RE WRITE 3

Topics: Metamorphic rock, Granite, Igneous rock Pages: 5 (1354 words) Published: February 21, 2015
Metamorphic and Igneous Rocks of the Hudson Highlands
3rd Field Report
The entire region of the Hudson Highlands underwent high-grade metamorphism, and at a series of locations different intrusions occurred during the Grenville Orogeny. Certain evidences to help back up this claim are the presence of gneissic rock and index minerals such as Siliminite and Garnet. Since the mineral composition indicates granulite facies, then its protolithic content is pelitic, meaning shale/mudrock. Also, a series of magmatic intrusions were shown the form of Lamprophyre, Granite, Pegmatite, and Diorite. Introduction

Located within the Hudson Highlands proto-continents collided giving rise to a major crustal thickening event called the Grenville Orogeny. It is important to study it because, it provides the geologic history of that particular area. In order to study the area, one must be able to identify detailed information about identifying rock types, mineral composition and associating it with its proper metamorphic facies. Methods

The Hudson Highlands was measured and analyzed along Harriman State Park, October 25th, 2013. Location was determined using Google maps on cellular devices equipped with Global Positioning Systems (GPS). Once location was determined, it was then recorded on the base map of Popolopen Lake Quadrangle. Features such as orientation, facies, fabric relations, and relative abundances of minerals were visually identified and recorded. Grain size and mineral composition were measured at a cm-m scale. Tools to help these features was a ruler, hand lens, Silva Compass, and the “Geology in the Field”, written by Robert R. Compton. Finally, an ACF/ACM diagram was plotted based on mineral composition. Data:

Metamorphic Rocks:
Garnet Siliminite Gneiss
Gneiss rock that is foliated and dark in color with bandings measuring up to 0.2cm, and the light bandings measuring up to 2cm. Minerals located within the dark bandings consists of Biotite (40%) measuring from 0.5-2cm. The light banding minerals consists of Plagioclase (5%) and Quartz (5%), measuring at 0.4-1cm. Mineral compositions also includes index minerals of Garnet (20%) and Siliminite (35%), with grain sizes ranging from 0.1-0.5cm. Which in turn, the aluminous minerals demonstrate that the rock is peltic and that the previous rock was shale/mudrock, which is determined by the abundance of quartz. Quartzo-feldspathic Gneiss

Gneiss Rock foliated and light in color. Light banding measures from 2.5-5cm, with minerals consisting of Quartz (45%) and Plagioclase (45%). Grain sizes range from 0.5-2cm. In the dark bandings, it measures 1cm and Biotite (10%) and its corresponding grain size ranges from 0.2-0.5cm. Intrusions of Pegmatite, Granite, and Lamprophyre with sharp contacts were observed. Biotite Gneiss

Gneiss rock foliated and dark in color. Dark banding measures at 3 cm consisting of Biotite (45%) with its corresponding grain size measuring at 0.2-1cm. The light bandings measuring at 1cm including Plagioclase (40%) and Quartz (15%) with grain sizes ranging from 0.1-2cm. Intrusions of Pegmatite and Granite were present and has sharp contact. Igneous Rocks:

Aphanetic mafic igneous rock that is extremely fine-grained and it intrudes the xenolith country rock. Granite:
Phaneritic Felsic Igneous Rock that has white, black, pink, and orange colors. Mineral Composition consists of Plagioclase (45%), Biotite (30%), Quartz (15%), and Potassium Feldspar (10%). Grain measuring 0.4-1cm,0.1-0.3cm, and 0.1-0.3cm, 0.2-0.4cm respectively. It intruded the Quartzo-feldspathic Gneiss towards the top of the unit and Biotite Gneiss with sharp contact. Pegmatite:

Phaneritic Felsic Igneous Rock with black, white, pink, orange and tan colors. Minerals consist of Quartz, Potassium Feldspar, Plagioclase, Pyroxene, and Amphibole. Grain sizes ranging from 2-5cm. It intrudes the Quartzo-Feldspathic Gneiss and Biotite Gneiss with sharp contact...
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