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GEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGY
Lecture 4
Field Characteristics of Intrusive Igneous Rocks
and
Introduction to the Sonju Lake Intrusion
Jan. 28, 2009
FORMS OF IGNEOUS INTRUSIONS
RING DIKES AND CONE SHEET
Isle of Mull, Scotland
LACCOLITHS AND LOPOLITHS
“The Duluth gabbro complex, for example, is a lopolith over 300 km across”(Winter, 2001, p. 64)
CONTACT ZONES OF INTRUSIONS
(Assimilated)
Thermal Metamophism of Country Rock
LARGE GRANITIC INTRUSIONSFOLIATED MARGINS
folia
tion
Alignment of phenocrysts in felsic magmas ~parallel to intrusion margins.
Phenocryst-rich magmas are commonly called “Crystal Mushes”
LARGE MAFIC INTRUSIONSVARI-TEXTURED (TAXITIC) MARGINS
TIMING OF INTRUSIONSYN/PRE-TECTONIC VS. POST-
TECTONIC
Vermilion Map M141, Jirsa and Boerboom, 2003
DEPTH OF EMPLACEMENT
Epizonal (<10km, <300oC) Brittle CR; sharp discordant contacts; strong metamorphic gradients; smaller plutonsMesozonal (5-15 km, 300-500oC) Ductile CR; sharp-gradational, discordant-concordant contacts; mod- strong metamorphic gradients; larger syn- to post-tectonic plutons
Catazonal (>10km, 450-800oC) Very ductile CR, gradational concordant sheared contacts, strong metamorphic gradients; syntectonic plutons
COMPOSITE INTRUSIONS
5 km
Tuolumne Intrusive Series, CaliforniaTuolumne Intrusive Series, CaliforniaBeaver Bay Complex, MinnesotaBeaver Bay Complex, Minnesota
MECHANISM OF MAGMA EMPLACEMENT
Diagrammatic illustration of proposed pluton emplacement mechanisms.
1- doming of roof
2- wall rock assimilation, partial melting, zone melting
3- stoping
4- ductile wall rock deformation and wall rock return flow
5- lateral wall rock displacement by faulting or folding
6- (and 1)- emplacement into extensional environment.
After Paterson et al. (1991), Contact Metamorphism. Rev. in Mineralogy, 26, pp. 105-206. © Min. Soc. Amer.
Winter (2001), Figure 4-34.
NEW IDEAS ON GRANITE BATHOLITH EMPLACEMENT
HYDROTHERMAL SYSTEMS
From Hudak (2006)
Sonju LakeIntrusion
The The Sonju Sonju Lake Lake Intrusion Intrusion
From MGS Map M-71 (Miller et al., 1989)
Cumulate RocksMafic igneous rocks interpreted to form by the accumulation of primocrysts on the margins (commonly the floor) of mafic layered intrusions
PROPOSED CUMULATE CLASSIFICATION FOR DC ROCKS
Main Attributes: It applies to rocks that show some igneous foliation or modal
layering and therefore solidified under conditions in which mineral phases segregated from their parent magma
It lists abbreviations of all minerals composing greater than about 2 modal percent in decreasing order of abundance regardless of their cumulus status
It denotes granular (cumulus) mineral phases with upper case letter abbreviations and interstitial (intercumulus) mineral phases with lower case abbreviations
Cumulus/Intercumulus Mineral CodesPP*/P/p - plagioclase F/f - Fe-Ti oxideO/o - olivine A/a - apatiteC/c - clinopyroxene (augite) -/b - biotiteI/i - inverted pigeonite -/a - amphiboleH/h - hypersthene, bronzite -/g - granophyre* used with anorthositic group rocks
EXAMPLES OF CUMULATE ROCK CODES
Cumulate Code Translation of Some Common Rock Types in the Duluth Complex
Ophitic augite troctolite - POcf Ophitic olivine gabbro - PcOf Augite-bearing oxide troctolite - POFc Ophitic olivine gabbroic anorthosite w/ poikilitic olivine -
PPocf Biotitic, feldspathic dunite with poikilitic plagioclase- Opb Intergranular, apatitic olivine oxide gabbro - PCFOA Ophitic biotitic augite leucotroctolite - POcbPossible modifications of the code: - preface with grain size designator (e.g. mPOcf, mcPPcfab)-designate well developed foliation of plagioclase with a bar over the P or PP-designate poikilitic texture with a ^ over the phase abbreviation (e.g. cPPĥ)-designate subpoikilitic texture with a ´ over the phase abbreviation (e.g mfPCó)
Leucogranite
Quartz ferromonzonite
Apatitic olivine ferromonzodiorite
Apatite olivine ferrodiorite
Ol-bearing oxide gabbro
Ol-bearing gabbro
Troctolite-augite troctolite
DuniteMelatroctolite
PCFOAg
PCFOAh
PCFoi
PC(O)fi
POcfi
OOP
Modal Rock NamesCumulus Code
Cumulus Mineral Mode
Modal Variations
Modal Variation and Cumulus Texture Modal Variation and Cumulus Texture
Cryptic Variation Cryptic Variation
SiO2 47.6TiO2 2.28Al2O3 14.0FeOt 14.7MnO 0.21MgO 8.3CaO 9.4Na2O 2.47K2O 0.55P2O5 0.30Volatiles 0.20Total 100.0mg# 50.2
Sc 34V 192Cr 111Co 75Ni 185Rb 20Sr 233Ba 171Y 20Zr 114Nb 17Hf 3.1La 14.7Ce 33.4Sm 4.1Eu 1.6Tb 0.8Yb 2.1 Lu .32
Bulk Intrusion CompositionBulk Intrusion Composition= Parent Magma= Parent Magma
= moderately evolved olivine tholeiitic basalt= moderately evolved olivine tholeiitic basalt
From Miller and Chandler (1998)and Miller and Ripley (1997)
Liquid Line of DescentLiquid Line of Descent
Calculated by summing composition of rock column above a specific horizon
Fractional Crystallization ModellingFractional Crystallization ModellingCHAOS 2 (NIELSEN, 1990)CHAOS 2 (NIELSEN, 1990)
Model Parameters : fO2 = -2 log QFM; trapped liquid = 20%
0 100 200 300 400 500 600
Cu (ppm)
Discovery of Stratiform Discovery of Stratiform PGE MineralizationPGE Mineralization
Skaergaard Intrusion
Feb. 1999