NEOMORPHIZMAJUNAID FOUAD KAREEMPROF.DR.HÜKMÜ ORHAN

JEOLOJİ MÜHENDİSLİĞİ ANA BİLİM DALI FEN BİLİMLERİ ENSTİTÜSELCUK ÜNİVERSİTESİ

2015/4/20-mondayJ_F_KAREEM@yahoo.com

ABSTRACT

Diagenesis of sediments includes processes with conspicuous effects, such as cementation that transforms unlithified sediments into hard limestones, quartz sandstones, or cherts. Diagenesis also involves the dissolution of sediments to produce small pores to large cave systems. Diagenesis also includes more subtle processes such as the alteration of marine trace element and stable isotope composition, In carbonate sediments,(Bathurst 1975).Neomorphism in carbonate rocks such as limestone is often increasingly which lead to forming the crystals with larger size, (James, N.P., 1991).

List of content1-1introduction.1-2 Neomorphism.2-Some previous studies were Neomorphism been noticed3-summaryreferences

1-1 INTRODUCTIONDiagenesis includes all the chemical, physical, and biological changes that occur after deposition, before metamorphism.(Friedman and Sanders, 1978).One of the Changes That Occur Within Rocks during Metamorphism is Neomorphism that it is A comprehensive term for all diagenetic transformations between one mineral and itself or a polymorph, whether the new crystals are larger or smaller or simply differ in shape from the previous ones. During neomorphism Pre-existing minerals/crystals are gradually consumed and their place in the same time occupied by new crystals of the same mineral or a polymorph, (Folk, 1965).

1-2 NEOMORPHISMCarbonate diagenesis takes place in three major regimes or realms: marine, meteoric and subsurface.1-2-1 Marine realm Includes the seafloor and the very shallow marine subsurface (MarinePhreatic environment) .strong dissolution of aragonite and calcite at two dissolution levels.1-2-2 Meteoric realmMeteoric Vadose environment Above water table, between land surfaceand meteoric phreatic zonePrincipal diagenetic processes:Dissolution, alteration of aragonite and high-Mg calcite to calcite.

1-2-3 Subsurface realm Burial environment Principal diagenetic processes:Physical compaction, chemical compaction, and additional chemical or mineralogical changes that may include dissolution, cementation, aragonite-to-calcite transformation, and replacement of calcite by another mineral such as dolomite. 

Neomorphism occurs in all three diagenetic realms but is particularly important in the meteoric and subsurface diagenetic environments, FIG (1). This process destroys original textures and fabrics and, when pervasive, may cause the entire rock to become recrystallized, (Boggs,2006).

During neomorphism New minerals form from chemical reactions between pre-existing minerals. And we can say that there is not necessarily any change in the chemical composition of rock.

FIG (1) The principle environments in which post depositional modification of carbonates occurs (from moore,c.h.,1989).

The atoms present in the rock simply rearrange to form new minerals. This happens if the pre-existing minerals are chemically unstable at metamorphic pressure and temperature (P&T) conditions. They react to form new, stable minerals. The metamorphic minerals that form provide information on the conditions (P & T) of metamorphism. This means That you can estimate the P & T of metamorphism (especially T) of many rocks based on the minerals present in the rock. For example, the presence of biotite & garnet together in a rock indicates metamorphism at (~850oF). However, some minerals are very resistant to Neomorphism; a prime example is quartz. Neomorphism happens in many rocks during metamorphism, and it often occurs in combination with recrystallization,(Metamorphic rocks handout, GEOL 1010, M. Bunds Instructor).

2-Some previous studies were Neomorphism been noticed:- 

 2-1 West Virginia, Wood County Trenton Formation, 9538ft.(http://www.wvgs.wvnet.edu/www/tbr/Data/Petrology/FIGURES/APPENDIX_II/Diagenesis_Final2.pdf)

 There is only neospar evident in this thin section. The lack of skeletal grains suggests that this rock was completely comprised of micrite prior to Neomorphism, Fig (2).

FIG(2)

2-2 West Virginia, Wood County Trenton Formation, 9593ft.

  This thin section is also dominated by microspar, although there are some remnants of skeletal grains. The skeletal remnants suggest that the rock was originally a wackestone. There is some micrite preserved between the neospar grain contacts, FIG (3).

FIG(3)

2-3 West Virginia, Wood County Trenton Formation, 9795ft.

The neospar in this thin section is slightly coarser than that observed above. There are also more abundant skeletal remnants present, FIG (4).

FIG4

3-Summary------Neomorphism is

-One of the major processes operating in carbonates and include all transformations between one mineral and itself or a polymorph.

-A major driving force for this is the metastability of aragonite, and, to a lesser extent, high-magnesium calcite.

-This process generally results in an increase in crystal size, and may lead to the destruction of all primary textures and features.

-Most neomorphism are a grading, leading to a general increase in crystal size. It occurs generally in fine grained limestones,

-Degrading neomorphismis not common, but has been recorded.

-Neomorphism a wet process, involving dissolution-reprecipitation.

REFRENCES 1- Bathurst, R. G. C. (1975) Carbonate sediments and their diagenesis. Elsevier, Amsterdam.2- Friedman, G. M. & Sanders, J. E. (1978) Principles of Sedimentology. John Wiley & Sons, New York, 792 pp.3- James, N.P., 1991, Diagenesis of carbonate sediments, a short Course: Geo.Soc.4- Folk, R. L. (1965) some aspects of recrystallization in ancient limestones. In: Dolomitization and Limestone Diagenesis.

5- Sedimentary Geology Dept. Earth Sciences National Central U. Taiwan Prepared by Dr. Andrew T. Lin.

6-Metamorphic rocks handout, GEOL 1010, M. Bunds Instructor. 7-Esmat, A. Abou, El-Anwar and Hamed, S.Mekky.8-http://www.wvgs.wvnet.edu/www/tbr/Data/Petrology/FIGURES/ APPENDIX_II/Diagenesis_Final2.pdf

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