G EOL 2312 I GNEOUS AND M ETAMORPHIC P ETROLOGY Lecture 4 Field Characteristics of Intrusive Igneous Rocks and Introduction to the Sonju Lake Intrusion Jan. 28, 2009

F ORMS OF I GNEOUS I NTRUSIONS

R ING D IKES AND C ONE S HEET Isle of Mull, Scotland

L ACCOLITHS AND L OPOLITHS “The Duluth gabbro complex, for example, is a lopolith over 300 km across” (Winter, 2001, p. 64)

C ONTACT Z ONES OF I NTRUSIONS (Assimilated) Thermal Metamophism of Country Rock

L ARGE G RANITIC I NTRUSIONS F OLIATED M ARGINS foliation Alignment of phenocrysts in felsic magmas ~parallel to intrusion margins. Phenocryst-rich magmas are commonly called “Crystal Mushes”

L ARGE M AFIC I NTRUSIONS V ARI - TEXTURED (T AXITIC ) M ARGINS

T IMING OF I NTRUSION S YN /P RE -T ECTONIC VS. P OST -T ECTONIC Vermilion Map M141, Jirsa and Boerboom, 2003

D EPTH OF E MPLACEMENT Epizonal (<10km, <300 o C) Brittle CR; sharp discordant contacts; strong metamorphic gradients; smaller plutons Mesozonal (5-15 km, o C) Ductile CR; sharp-gradational, discordant-concordant contacts; mod- strong metamorphic gradients; larger syn- to post-tectonic plutons Catazonal (>10km, o C) Very ductile CR, gradational concordant sheared contacts, strong metamorphic gradients; syntectonic plutons

C OMPOSITE I NTRUSIONS 5 km Tuolumne Intrusive Series, California Beaver Bay Complex, Minnesota

M ECHANISM OF M AGMA E MPLACEMENT 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 © Min. Soc. Amer. Winter (2001), Figure 4-34.

N EW I DEAS ON G RANITE B ATHOLITH E MPLACEMENT

H YDROTHERMAL S YSTEMS From Hudak (2006)

Sonju Lake Intrusion

TheSonjuLakeIntrusion From MGS Map M-71 (Miller et al., 1989)

Cumulate Rocks Mafic igneous rocks interpreted to form by the accumulation of primocrysts on the margins (commonly the floor) of mafic layered intrusions

P ROPOSED C UMULATE C LASSIFICATION 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 Codes PP*/P/p- plagioclaseF/f- Fe-Ti oxide O/o- olivineA/a- apatite C/c- clinopyroxene (augite)-/b- biotite I/i- inverted pigeonite-/a- amphibole H/h- hypersthene, bronzite-/g- granophyre * used with anorthositic group rocks

E XAMPLES OF C UMULATE R OCK C ODES 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 - POcb Possible 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 Dunite Melatroctolite PCFOAg PCFOAh PCFoi PC(O)fi POcfi O OP Modal Rock Names Cumulus Code Cumulus Mineral Mode Modal Variations Modal Variation and Cumulus Texture

Cryptic Variation

SiO247.6 TiO22.28 Al2O314.0 FeOt14.7 MnO0.21 MgO8.3 CaO9.4 Na2O2.47 K2O0.55 P2O50.30 Volatiles0.20 Total100.0 mg# 50.2 Sc34 V192 Cr111 Co75 Ni185 Rb20 Sr233 Ba171 Y20 Zr114 Nb17 Hf3.1 La14.7 Ce33.4 Sm 4.1 Eu1.6 Tb0.8 Yb2.1 Lu.32 Bulk Intrusion Composition = Parent Magma = moderately evolved olivine tholeiitic basalt From Miller and Chandler (1998) and Miller and Ripley (1997) Liquid Line of Descent Calculated by summing composition of rock column above a specific horizon

Fractional Crystallization Modelling CHAOS 2 (NIELSEN, 1990) Model Parameters : fO2 = -2 log QFM; trapped liquid = 20%

Cu (ppm) Discovery of Stratiform PGE Mineralization Skaergaard Intrusion Feb. 1999