The Archean & Proterozoic 4.0 Ga to 543 Ma. Growth of Continental Crust There is some considerable debate regarding the rate at which continental crust.

Slides:



Advertisements
Similar presentations
Crust formation in the early Earth prior to the onset of subduction
Advertisements

Rocks.
Igneous Rock Formation
Unit 3 Rocks, Soil, Erosion and Mass Movements
PLATETECTONICS Or Are we dancing on an eggshell? Is there a magma ocean below? …and much more…
Plate Tectonics and Mineralization Structural features of the Earth Major plates & Plate boundaries Plate tectonic cycle Mineralization.
CHAPTER 5: Igneous Rock.
Igneous Rocks and Classifying Igneous Rocks
CH. 5 – Igneous Rocks   What are igneous rocks?   Formed by the hardening of magma.   “Ignis” means fire   What is the difference between magma.
Earth’s Interior and Geophysical Properties Chapter 17.
Lecture Outlines Physical Geology, 14/e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plummer, Carlson &
GEOL- 103 Lab 2: Igneous/Metamorphic Rocks. Igneous Rocks Form as molten rock cools and solidifies General characteristics of magma Parent material.
Tim Horner, CSUS Geology Department Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks Physical Geology 13/e, Chapter 3.
Igneous Rocks. Summary 1. The Rock Cycle 2. Formation of Igneous Rocks 3. Classification of Igneous Rocks.
III. Igneous Rocks Minerals Crystallized from Melts 1. The Rock Cycle 2. Formation of Igneous Rocks 3. Classification of Igneous Rocks 4. Igneous Rocks.
Lecture Outlines Physical Geology, 14/e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plummer, Carlson &
Field trip: This Saturday VOLUNTARY Meet here (to carpool?) and then drive to Bridger to rendezvous with Dr. Zwick at 9 AM. Bring lunch and something.
Quiz 1 Monday. Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks Physical Geology, Chapter 3.
Chapter 5-Igneous Rocks
Intermission: Intermission: Plate Tectonics. National Oceanic and atmospheric Administration/National Geophysical Data Center.
Igneous Rocks
Modern Concepts in Earth Science Igneous Rocks Formed in Rift Igneous Rocks Formed Above Subducting Plate Course 7 – Igneous Rocks.
Earth Science Standard 3c: Students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including.
IGNEOUS ROCKS rock = mixture of minerals, mineraloids, glass, or organic matter bound together in some way 1. magma is parent material for all rocks 2.
Melting Weathering Deposition & Lithification Burial, Heat, Pressure = Metamorphism Crystallization.
Atwood Quarry, Port Clyde, ME Chelsea Sonksen Craters of the Moon NP Will Junkin.
The Rock Cycle A rock is a naturally formed, consolidated material usually composed of grains of one or more minerals The rock cycle shows how one.
1 SGES 1302 INTRODUCTION TO EARTH SYSTEM LECTURE 15: Classification of Igneous Rocks.
Igneous Rocks Textures. The Rock Cycle A rock is a naturally formed, consolidated material usually composed of grains of one or more minerals The rock.
The Rock Cycle A rock is a naturally formed, consolidated material usually composed of grains of one or more minerals The rock cycle shows how one type.
3.2 Igneous rocks form from molten rock
The Rock Cycle: Igneous Rocks
Igneous Rocks. Rock Cycle Types of rocks Area of exposure on surface and volume fraction.
ESCI 101: Lecture The Rock Cycle & Igneous Rocks February 23, 2007 Copy of this lecture will be found at: With Some.
Chapter 4 Rocks & Igneous Rocks. Rock Definition A naturally occurring, solid Composed of one or more minerals.
Chapter 4 Igneous Rocks.
IGNEOUS ROCKS.
Chapter 4 ~ Intrusives ~.
Chapter 5: Igneous rocks
The Rock Cycle A rock is composed of grains of one or more minerals The rock cycle shows how one type of rocky material is transformed into another Igneous.
Lecture Outlines Physical Geology, 12/e Plummer & Carlson Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Igneous Rocks and Their Origin Chapter 5. Igneous rocks - Formed from volcanic eruptions - either external or internal Sedimentary rocks - Formed from.
Igneous Rocks Mr. Ahearn Earth Science What are Igneous Rocks? Rocks that cooled and crystallized directly from molten rock, either at the surface.
The Origins of Magma and Igneous Rocks
Igneous Rocks. The Rock Cycle The continuous and reversible processes that illustrates how one rock changes to another. “ One rock is the raw material.
Rocks and the Rock Cycle Rocks are made of one or more minerals. Each rock belongs to one of three major types; based on how it is formed. Rock Types 1.
Chapter 4 Rocks & Igneous Rocks. Rock Definition A naturally occurring consolidated mixture of one or more minerals e.g, marble, granite, sandstone, limestone.
Archean Rocks Best, Chapter 15A.
Igneous Rocks and Their Origin Chapter 3. The Rock Cycle A rock is composed of grains of one or more minerals The rock cycle shows how one type of rocky.
Igneous Rocks Text ref. Ch5 (pg. 98).
How Earth’s Rocks Were Formed
Igneous rocks form as molten rock cools and solidifies General characteristics of magma Parent material of igneous rocks Forms from partial melting of.
OPHIOLITE Ophiolite (Gk. Ophio – snake; lite- stone from Gk. Lithos) Ophiolite- distinctive assemblage of mafic plus ultramafic rocks; fragments of oceanic.
Chapter 4: Igneous Rocks. Introduction Igneous rocks = formed from “fire” Magma = completely or partially molten rock Lava = magma which reaches surface.
Igneous Rocks Intrusive and extrusive rocks formed from the cooling and crystallization of magma.
By: Faisal Andrew Travis Adrian.  Geological Significance  Texture  Characteristics  Composition  Structure  Setting  Classification  Composition.
Layers of the Earth The Layers of the Earth are the Inner Core, Outer Core, Mantle and Crust.
Rocks.
3.2 Rocks.
Lecture Outlines Physical Geology, 12/e
Understanding Earth Chapter 4: IGNEOUS ROCKS Solids from Melts
GEOLOGY 101 Course Website: Today: Chapter 6
Chapter 4 Rocks & Igneous Rocks.
Chapter 5 Igneous Rocks Section 5.1.
Chapter 4.
Igneous Rocks Chapter 3.
Rocks.
Rocks (Igneous).
Rocks.
Presentation transcript:

The Archean & Proterozoic 4.0 Ga to 543 Ma

Growth of Continental Crust There is some considerable debate regarding the rate at which continental crust has been added to the earth. Slow-growth models Rapid growth models Pulse & Intermediate growth models

Onset of Plate Tectonics? There is actually considerable debate about when modern-style plate tectonics began on the planet. Through secular cooling and decay of long and short lived radioisotopes, the Earth’s thermal regime should be decreasing through time. The early hot earth may have inhibited subduction of oceanic crust (i.e. the convection and heat in the mantle would have stopped subduction. Average age of subducted crust today is ~125 Ma. Contrary View: The early oceanic crust was of a different (denser) composition and therefore able to subduct because of its negative buoyancy.

In terms of the thermal budget for the Earth, the overall heat budget from the decay of radioactive elements in the Late Neoproterozoic is not significantly different than today.

Komatiites Komatiites are very high temperature lavas with MgO contents up to 33%. Uprise from great depths is the easiest way to achieve such high liquid temperatures. Now it used to be thought that such high temperatures (>1600°C) could only be achieved in the mantle of the early Earth (Archaean).

“Spinnefex” fabric in Komatiite lavas-Africa

Cretaceous Komatiites It was thought that komatiites could not form in younger times, but they were discovered on the island of Gorgona (near Colombia). Some newer ideas are that komatiites are formed from deep mantle melts (where temps are higher). The Archean still had high temps and it is possible that a Komatiitic ocean crust could subduct.

Crustal Motion There is clear evidence that continental drift did occur in the Archean. Paleomagnetic studies on Archean-age rocks show that the crustal blocks did move, but continental drift is not the same thing as plate tectonics.

Ophiolites Ophiolites-Pieces of oceanic plate that have been thrusted (obducted) onto the edge of continental plates.

How do we know? Marine Sediments on Continental block Fault block melange Metamorphic sole (base) and peridotite (Mg-silicate rock. Layered Gabbro- Chemical equivalent of basalt. Massive Gabbro Feeder Dikes Pillow Basalts & Marine Sediments

Franciscan melange

Peridotite

Layered Gabbro in Oman

Massive Gabbro

Sheeted Dyke Complex

Pillow Basalts

Ocean Floor Sediments

Ophiolites indicate Subduction of Oceanic Crust. Eldredge Moores (1994) suggested that ophiolites became common around 1000 Ma and this marked the onset of modern-style plate tectonics. A dismembered ophiolite was found in Dongwanzi China by Tim Kusky (2002). The ophiolite is 2.5 Ga and provides evidence that modern-style plate tectonics was already underway at 2.5 Ga. Others argue that the time interval from ~ Ga marked the onset of modern-style plate tectonics.

Are we arguing about silly things? Possibly. However, we use modern plate tectonic models to help us identify regions of mineral wealth. What is it that we know positively? –Continental crust had formed in the Archean –Continental crust was moving in the Archean –Mafic crust in the Archean was formed in a hotter environment –Most of that mafic crust is gone (subduction).

Types of Archean Continental Crust Granite-Greenstone Belts Tonalite-Trondhjemite Gneisses (TTG’s)

Tonalites-Trondhjemites Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. Mineral assembly is composed typically of plagioclase, more than 20% of quartz and rare alkali feldspar. Amphiboles and pyroxenes are common accessory minerals. Trondhjemite is a variety of tonalite where biotite is the only mafic mineral.igneousintrusiverockphaneriticplagioclasequartzfeldsparAmphibole pyroxenebiotite Both are associated with subduction and the formation of island arcs.

Granite-Greenstone Belts Granites are an intrusive felsic rock that forms at temperatures around 800 C. Greenstones are low-grade metamorphosed basalts. Their association in the Archean is quite strange. They are likely tectonic slices (fault- bounded)