Rock Units

Mer av detta

interactions in the physical environment

av Fernando De Francesca

Precambrian Era

av Nguyen Denton

Natural Systems: What Is Fixed?

av Paige Cunningham

GEOLOGIC TIME SCALE

av Esteban Jaramillo

cover about 7% of the Egyptian Basement

Wadi Feiran in the south western part of Sinai

Gabal Meatiq in the central Eastern Desert

Migif ‐ Hafafit area in south Eastern Desert

The rocks revealed the following age succession

Ultramafic rocks of ophiolitic affinity. (Oldest)

Foliated metagabbros (the hornblende gneisses?) pertaining to an old oceanic crust

Biotite schists (interlayered with bands rich in hornblende)

Psammitic gneisses (probably derived from continental sources)

Intrusive calc‐ alkaline metagabbros

Gneissic tonalite. (Youngest)

associated rocks are of sedimentary & igneous derivation

occur within a spectacular Precambrian structure

depend on the origin

Gneisses of igneous origin(Orthogneiss)

The oldest igneous rocks in the area are foliated metagabbros (hornblende gneisses) similar in their geochemical characters to mid ‐oceanic ridge basalts (MORB) and consequently they are believed to pertain to an ophiolitic assemblage

Gneisses & schists of sedimentary origin (psammitic)

consist mainly of quartz (50 ‐ 80%), potash feldspar, plagioclase & mica

The Younger Granites

Hussein (1982)

G III

formed in no orogeny OR within plate tectonic setting

alkaline to per alkaline granit

G II

formed by melting of lower crust

formed in active margin (suture)

calc alkaline red to pink granit

G I

formed as subduction related granit

older grey shaitian granit

El Gaby (1975)

Post-orogenic alkali granites

rich in perthite & k-feldspar

alkaline to peralkaline in composition

Circular to oval outline (sharp intrusive contact)

Late orogenic calc-alkali granites

elongated bodies parallel to the regional structure of the area

ages can be subdivided into two major events

2- Katherina event: spanning the time interval 570 to 530.

1- Dokhan event: spanning the time interval 620 to 570 and

within the range 620 to 530

Their contacts with the surrounding country rocks are sharp.

usually with rounded or oval outlines.

red to pink color

the last phases commonly possess per-alkaline tendencies

intrusive granitic rocks ranging in composition from calc-alkali to alkali granites

Eastern desert

per-alkaline granites

Gabal Gharib

Gabal El Zeit

Hammamat Group

Intercalation of dokhan with base of hammamat group

indicate sedimentation in the same time

Akad & Nweir divided it into 2 formations

Shihyimia formation

divided into three members

Um Hassan Grey Wake Member

Um Had Conglomerate member

Rasafa siltstone member (Bottom)

red, grey, green

unconformably overlain dokhan volcanics & other rock units

the base of succession

Akad first described At Wadi Igla

Igla Formation

Red Beds

Cross Cutting ralationship

Hammamt is older than younger granit

REASON: Um had granit cutting hammamat

Hammamat is younger than dokhan colcanics

REASON: base of hammat included babbles of dokhan volcanics

Isotopes

Some Of it are contact metamorphosed

deposited in intermountain basins

deposited after rapid uplift

Considered as post orogenic event

Unmetamorphosed sedimentary succession

qift - qusier road

wadi shihymia

Wadi Kareem

Wadi Hammat

Wadi Igla

Dokhan Volcanics

other information

formed in Active Continental Margin

thickness about 120 m and flow 50 - 200 m

After Deposition of Arc Graditoid

Preceding the deposition of Hammamat

Intercalation with the base of hammamte

indicate that Hammamat formed in the final phase of dokhan eruption

Boulders of dokhan on the base of Hammamat

Have Rock Variety of Imperial Porphyry

Pg +Hb

red, purple

rich in Mn

Withamite

porpheritic

Qz Andesite

colors

red to reddish purple

Intermediate to acidic volcanic rocks

Andesite, Rhyolite, Dacite, Rhyodacite

Consists Of Volcanic Flows Intercalate with tuffs and ignimbrite (cryptocrystalline glassy fragments)

North Eastern Desert Gabal Dokhan

Arc granitoids (Syn‐ tectonic granitoids)

formed in island arc tectonic setting

form important rock unit in Egyptian basement around 40% of basement rocks

Shazly

Post Orogenic Granit

Late Orogenic Granit

Syn orogenic Granit

More Deformed (The Oldest)

Shurman

Shaitian Granit

The Oldest

El Ramly, Akad & Nweir

Younger red Pink Granit

Hume

Grey Granit

Gattarian Granit

Gabal Gattar

developed during three phases

Meatiq Event (670 - 630) Ma

Hafafiet Event (720 - 670) Ma

Shaitian Event (850 - 800) Ma

Cataclastic Or Deformed granodiorite

Rich in Pg

Grey Older Granit

Alkali Granite

Qz Diorite

Wadi Shait

Metavolcanics

Other Information

Metasediments

display the alternation or interfingering of sedimentation (flysch type) and volcanism

This led Akaad and Noweir (1969) to group together the metasediments and metavolcanics in one group named Abu Ziran Group

mainly in a low grade metamorphism to medium grade

defined by El Ramly and Akaad (1960) as including a succession of “geosynclinal sediments"

Serpentinites

Their type area is taken as the Barramiya

form well‐defined belts associating the metavolcanics & metasediments

evolved in island arc or volcanic arc tectonic setting

divided into

Younger metavlocanics (ymv)

intermediate to acidic

overlies and interfinger with metasediment

dominantly andesitic volcanic

older Metavolcanics (omv)

basic

represent part of ophiolite assembleg

thick mutinous succession of pillow meta basalt associated with meta gabbro

Age

Characteristics (Composition)

range in composition from basic to acidic

sequence of basic to intermediate rocks

represent early stage of island arc

interpreted as early phase of geosyncline filling

associated and partially alternating with meta sediments

Represent groups of regionally metamorphosed volcanic rocks

south Eastern Desert

Skiekh Shadly

identified into four mappable units

Ophiolites and ophiolitic mélange

a mappable rock unit characterized by the inclusion of fragments and blocks, of all sizes which may reach several kilometers, embedded in a fragmented and generally sheared matrix

Ophiolite

Locality

Qift‐ Quseir road

Wadi Ghadir

The ophiolites occur as allochthonous units in a melange assemblage

Melange

The melange is divided into two facies (depending on the relation to the source of its ophiolitic components)

The distal facies

is composed of low‐grade schists mostly pelitic. The melange contains both continental and oceanic components indicating deposition in an oceanic trench over a subduction zone

The proximal facies

is composed of rounded and fragmented rock boulders varying greatly in size in a matrix of schistose mudstone.

Deep marine sediments

Pillowed basalts

Gabbro Complex

Serpentinized peridotites

distributed throughout the Nubian‐ Arabian Shield

Eastern Desert

complete ophiolite section is

Ultramafic rock sequence

Cumulate gabbro

Olivine gabbro

Sheeted dyke complex

Pillow lava: pillow basalts

TOP- Pelagic sediments: cherts, limestone

Classification

now deal with ophiolites as fragments of oceanic plates that have transported in thrust zones

associated with subduction zones or thrusted onto into their continental setting by a process of obduction

defined as an assemblage of mafic and ultramafic lavas and hypabyssal rocks

associated with greywackes and cherts in geosynclines

lithologic association of rocks thought to be typical of oceanic crust that have been thrusted up into their continental setting by the obduction process