Presentation on theme: "Mahrous M. Abu El-Enen Faculty of Science, Mansoura University Igneous and metamorphic Petrology."— Presentation transcript:
Mahrous M. Abu El-Enen Faculty of Science, Mansoura University Igneous and metamorphic Petrology
Metamorphic minerals In addition to minerals that occurred in igneous rocks such as (quartz, feldspars, micas, amphiboles, pyroxenes, olivine) and sedimentary rocks (calcite, quartz), metamorphic rocks are characterized by own minerals such as: - Garnet- Staurolite-Talc- Serpentine - Kyanite- Sillimaniteetc. Mineral assemblage in metamorphic rocks is function of P-T-X conditions, e.g. with increase P-T conditions in metamorphosed shale: Chlorite (low P-T conditions) → Biotite → Garnet → Staurolite → Kyanite Sillimanite (high P- T conditions).
Development of Metamorphic Rocks The yielded metamorphic rocks, with specific mineral composition and textures is a function of: Protolith nature i.e: whole rock chemistry : sedimentary (shale, limestone, sandstone) or igneous rocks (acidic, intermediate, basic, ultrabasic). Metamorphic conditions (the intensity of T and the intensity and type of P (directive or lithostatic) influence and the presence or absence of fluids and their chemistry during metamorphism). It could low-, medium-, and high-grades. Time (who long the rock subjected to T and P?. By which the grain size was evolved, and the reactions were proceed).
Regional metamorphism of shale yielded a foliated rocks, usually mica-rich, and characterized by increase of grain- size with increasing the metamorphic grades to form: slate → schist → gneiss → migmatite. Metamorphism of shale
Slate -Slate is usually dark, very-fine grained, foliated metamorphic rock. - Slate is derived from shale by regional metamorphicm in the lowest grade condition (<300°C) of shale. - slate is characterized by a dull luster and strong cleavage. - Slate gets a pronounced cleavage direction, so it breaks along flat planes. - With further metamorphism slates turned to schists and gneisses.
Schist - Schist is a general term of medium-grained foliated rocks. - It is largely formed due to regional metamorphism of shale under medium-grade conditions ( °C). - Schist is usually described according to their predominant minerals (e.g. mica schist, garnet-mica schist, hornblende schist, talc-schist, etc.)
Gneisses - Gneisses are coarse-grained foliated rocks. - They are formed due to metamorphism of shale and/or acidic igneous rocks under high-grade conditions (>500 °C). - They are usually described according to their predominant minerals (e.g. biotite-gneiss, hornblende gneiss, etc.)
Migmatite -Migmatite is a composite rocks that linked between the metamorphic and igneous rocks. - It is usually formed due to partial melting of gneisses. - It is composed of two different parts: 1) the leucocratic part of igneous appearance, and 2) the melanocratic part of metamorphic origin.
Regional and/or thermal metamorphism of carbonate sedimentary rocks yielded marble rocks of different grain size and granulose texture. It is largely composes of calcite and/or dolomite. It is usually non-foliated. Metamorphism of Carbonate Rocks
Regional and/or thermal metamorphism of sandstones yielded quartzite rocks. Quartizite is a foliated or non foliated metamorphic rock composed predominantly of quartz (> 90 vol. % quartz). Metamorphism of sandstones
Metamorphism of basic igneous rocks (basalt or gabbros) yielded an amphibole and pyroxene rich rock as: Greenschist → amphibolite → eclogite with increasing metamorphic grades - Greenschist is a low-grade, fine-grained rock composed of green minerals. - Amphibolites : foliated or non-foliated fine to medium grained rock composed dominantly of hornblende and plagioclase. : - Eclogite : a green and red coarse-grained metamorphic rock that contains clinopyroxene and garnet. Metamorphism basic igneous rocks
Metamorphism of ultramafic igneous rocks (dunite or predotite) yielded talc schist or serpentinites: - Talc schist or soapstone consists largely of talc mineral with perfect foliation. It is derived from ultramafic rocks through hydrothemal alteration Serpentinites are green to dark-gray rock (either foliated or non-foliated), composed of minerals of the serpentine group. It forms by regional metamorphism of ultramafic rocks of the oceanic lithosphere due to alteration with water excess. Metamorphism of ultramafic igneous rocks
Hornfels Hornfels are fine-grained rock that formed due to thermal metamorphism of country rocks (e.g. shale). Mineral constituents charcterize by its random orientation. Usually bedding and other structures could be preserved.