Transcript GEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGY Lecture

GEOL 2312
IGNEOUS AND METAMORPHIC
PETROLOGY
Lecture 1
Introduction to Igneous Petrology and
Earth’s Physical and Chemical Structure
Jan. 13, 2016
A Fundamental Dilemma to the Study of Igneous and
Metamorphic Rocks and the Processes that Create Them
ACCESS
THE REALM OF
IGNEOUS AND
METAMORPHIC
ROCKS
IGNEOUS PETROLOGY
“Study of Rocks formed by the Crystallization of Magma”
Geologists as Journalists: What, Where, When, Why
What do we want to know about magma?
What do we want to know about crystallization processes?
How do we study igneous rocks to address these questions?
TOOK A WHILE TO GET HERE
A.G. Werner (1787) - Developed a chronostratigraphy of the
Earth’s crust that was based on progressive deposition of
rocks from a gradually subsiding ocean. The theory was
nearly universally accepted in the late 1700’s. Defined five
crustal units: Primitive Series – crystalline rocks considered to be the first
precipitates from the ocean before the emergence of land.
Transition Series - more indurated sedimentary sequences
that were the first orderly deposits from the ocean.
Secondary Series - the remaining, obviously stratified
fossiliferous rocks and certain associated "trap" rocks. These
were thought to represent the emergence of mountains from
beneath the ocean and were formed from the resulting
products of erosion deposited on their flanks.
Alluvial Series - poorly consolidated sands, gravels and
clays formed by the withdrawal of the oceans from the
continents.
Abraham Gottlob Volcanic Series - younger lavas flows demonstrably
associated with volcanic vents. Werner believed that these
Werner
rocks reflected the local effects of burning coal beds.
1749-1817
NEPTUNISM
Interesting Interpretations:
- Primitive granites, highly metamorphosed rocks, basalts
flows and diabase dikes are crystalline precipitates from
the universal ocean
- Mountains reflect the original chaotic landscape of the
earth; they are static, fixed in space and time
- Volcanoes are minor, geologically unimportant elements
of the crust created by the subterranean combustion of
coals seams.
VULCANISTS
Auvergne Volcanoes , S. France
Early Challenges to Werner’s theory:
- Where did the water go???
- The Auvergne volcanoes rest on granite (primitive rocks)!
- Italian and French scientist showed that “trap rock”
interlayered with sedimentary rocks were identical to recent
basalt flows and thus were formed from molten lava and
were not precipitates from seawater.
PLUTONISM
James Hutton (1726-1797) – The Father of Modern Geology
A member of the Edinburgh Oyster Club that included economist Adam
Smith, mathematician John Playfair, philosopher John Hume, and chemist
Joseph Black
1788. Theory of the Earth; or an investigation of the laws observable in the
composition, dissolution, and restoration of land upon the Globe.
Principal Concepts
• The current landscape is a balance between
rejuvenation (uplift) and destruction (erosion) of
the earth’s surface
• The earth is eternally dynamic and everchanging (“No Vestige of a Beginning, No
Prospect of an End”)
• The internal heat of the earth is responsible for
uplift of mountains and the igneous origin of
granite and basalt?; reinforced by melting
experiments of Hall (1792)
Melting
Experiments
Crystallization Experiments
COMPONENTS OF SCIENTIFIC “STUDY”
OBSERVATIONS/INTERPRETATIONS OF
EXPERIMENTS SIMULATING THE NATURAL WORLD
COMPONENTS OF SCIENTIFIC “STUDY”
OBSERVATIONS/INTERPRETATIONS
OF THE NATURAL WORLD
COMPONENTS OF SCIENTIFIC “STUDY”
OBSERVATIONS/INTERPRETATIONS OF
THEORETICAL MODELS THE OF NATURAL WORLD
Cobra MELTS Interface
Ghiorso & Sack (1995)
PHYSICAL AND CHEMICAL STRUCTURE OF
EARTH
HEAT SOURCES AND TRANSFER IN THE EARTH
1. Heat from the early accretion and differentiation of
the Earth still slowly reaching surface
2. Heat released by the radioactive breakdown of
unstable nuclides
Heat transferred by:
1. Radiation – transfer to another mediuim
2. Conduction – transfer kinetic energy from hotter to colder
3. Convection/Advection – movement of material of different
densities controlled by temperature and composition
The Geothermal Gradient
PRESSURE AND THERMAL GRADIENTS
From Winter (2001)
COMPOSITION OF THE EARTH
How Do We Know?
- Mantle Xenoliths
- Seismic Data
- Density Constraints
- Meteorites
- stony ~mantle
- iron ~core
- chondrites ~whole
earth
Plate Tectonics drives Two Stages of Crust-making
1. Mantle partially melts to make ocean crust
2. Ocean crust melts to make continental crust
THE
GEOTHERMAL
GRADIENT
Fig 1.13. Pattern of global heat flux variations compiled from
observations at over 20,000 sites and modeled on a spherical
harmonic expansion to degree 12. From Pollack, Hurter and
Johnson. (1993) Rev. Geophys. 31, 267-280.
Cross-section of the mantle based on a seismic tomography model.
Arrows represent plate motions and large-scale mantle flow and
subduction zones represented by dipping line segments. EPR =- East
pacific Rise, MAR = Mid-Atlantic Ridge, CBR = Carlsberg Ridge.
Plates: EA = Eurasian, IN = Indian,
PA = Pacific, NA = North American, SA = South American, AF =
African, CO = Cocos. From Li and Romanowicz (1996). J. Geophys.
Research, 101, 22,245-72.
PLATE
TECTONICS
From: quakeinfo.ucsd.edu/%7Egabi/sio15/Lecture04.html
“Slab Pull” is thus much more effective than “Ridge Push”
But both are poor terms: “slab pull” is really a body force (gravity
acting on the entire dense slab..
The old question of whether convection drives plate tectonics or not is also
moot: plate tectonics is mantle convection.
The core, however, cools by more vigorous convection which heats the
base of the mantle by conduction and initiates plumes (lower viscosity)
MANTLE
DYNAMICS
Is the 670 km transition a
barrier to whole-mantle
convection?
Maybe?
Partly?
No?
Figure 1.14. Schematic diagram
of a 2-layer dynamic mantle model
in which the 660 km transition is a
sufficient density barrier to
separate lower mantle convection
(arrows represent flow patterns)
from upper mantle flow, largely a
response to plate separation. The
only significant things that can
penetrate this barrier are vigorous
rising hotspot plumes and
subducted lithosphere (which sink
to become incorporated in the D"
layer where they may be heated
by the core and return as plumes).
Plumes in core represent
relatively vigorous convection (see
Chapter 14). After Silver et al.
(1988).
TECTONO-MAGMATIC ENVIRONMENTS
1. Mid-ocean Ridges
2. Intracontinental
Rifts
3. Island Arcs
4. Active Continental
Margins
5. Back-arc Basins
6. Ocean Island Basalts
7. Miscellaneous IntraContinental Activity

kimberlites, carbonatites,
anorthosites...