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