D. Barrie Clarke

Searching for the Geological Source of the Titanic Gravestones in Halifax, Nova Scotia

Education

• B.Sc., University of Toronto, (1964)
• M.A., University of Toronto, (1965)
• Ph.D., University of Edinburgh, (1969)

Publications

Clarke, D. B. (1995) Cordierite in felsic igneous rocks; a synthesis. Mineralogical Magazine 59, 311-325.
This paper is my first systematic investigation of a single mineral phase showing that more than one kind of cordierite can exist in granitic rocks. At the very least, textural evidence alone shows that there has to be magmatic and xenocrystic cordierite, but there might also be new cordierite that grew in peritectic melting reactions of country rocks.

Clarke, D. B., Henry, A. S., and White, M. A. (1998) Exploding xenoliths and the absence of "elephants' graveyards" in granite batholiths. Journal of Structural Geology 20, 1325-1343.
A catchy title with an important message. A large xenolith in the SMB shows many stages of physical disintegration from the decametre scale to the millimetre scale. We reasoned that, in the limit, large xenoliths could eventually fragment to become completely disaggregated xenocrysts, and if the mineral assemblages of the country rock and granite were identical, one could not easily determine the origin of any given mineral grain in the granite. Long ago, Bowen had talked about contaminants being “strewn about”, thus making them difficult to distinguish from magmatic phases.

Clarke, D. B., Fallon, R., and Heaman, L. M. (2000) Interaction among upper crustal, lower crustal, and mantle materials in the Port Mouton Pluton, Meguma lithotectonic zone, Southwest Nova Scotia. Canadian Journal of Earth Sciences 37, 579-600.
The Port Mouton satellite pluton shows clear physical evidence for mafic-felsic magma mingling as well as for extensive contamination by the Meguma Supergroup country rocks. In this paper we tried to untangle the complex combined effects of mantle and crustal contamination in the PMP.

Erdmann, S., Clarke, D. B. and MacDonald, M. A. (2004) Origin of chemically zoned and unzoned cordierites from the South Mountain and Musquodoboit batholiths, Nova Scotia. Transactions of the Royal Society of Edinburgh: Earth Sciences 95, 99-110. (also, Special Paper - Geological Society of America 389, 99-110)
Cordierite encore. While not primarily a contamination investigation, nevertheless chemical zonation patterns in cordierites of the peraluminous granites of southern Nova Scotia may be relevant.

Clarke, D. B., MacDonald, M. A. and Erdmann, S. (2004) Chemical variation in Al2O3-CaO-Na2O-K2O space; controls on the peraluminosity of the South Mountain Batholith. Canadian Journal of Earth Sciences 41, 785-798.
Why does the peraluminosity of the SMB increase with increasing chemical evolution? This work shows that closed-system fractional crystallization and open-system country-rock contamination must be involved.

Clarke, D. B., Dorais, M., Barbarin, B., Barker, D., Cesare, B., Clarke, G., El Baghdadi, M., Erdmann, S., Foerster, H-J., Gaeta, M., Gottesmann, B., Jamieson, R. A., Kontak, D. J., Koller, F., Gomes, C. L., London, D., Morgan, G. B. VI, Neves, L. J. P. F., Pattison, D. R. M., Pereira, A. J. S. C., Pichavant, M., Rapela, C. W., Renno, A. D., Richards, S., Roberts, M., Rottura, A., Saavedra, J., , Toselli, A. J., Ugidos, J. M., Uher, P., Vilaseca, C., Visona, D., Whitney, D. L., Williamson, B., Woodard, H. (2005) Occurrence and origin of andalusite in peraluminous felsic igneous rocks. Journal of Petrology 46, 441-472.
We keep plugging away at those mineralogical expressions of peraluminosity, and in this paper we discover that, whereas many of the andalusites of peraluminous granites are magmatic, some are definitely xenocrystic. Only a careful investigation of texture and composition can resolve the two origins.

Clarke, D. B. and Erdmann, S. (2005) Field Trip A1; Contamination in the South Mountain Batholith and Port Mouton Pluton, southern Nova Scotia. Atlantic Geoscience Society Special Publication 21.
A richly illustrated field guidebook for many of the best contamination localities in the SMB and PMP.

Samson, H. R. (2005) Origin of Sulfides in the Contact Granodiorites of the South Mountain Batholith, Nova Scotia. BSc Honours Thesis, Dalhousie University, Halifax, NS.
In contrast to many of the other phases we have investigated, the sulfides were not part of the original mineral assemblage of the granites, so all sulfides in the contact granodiorites are foreign. This thesis began the investigation and we now have a manuscript under review (see below).

Lackey, J. S., Erdmann, S., Clarke, D. B., Fellah, K. L., Nowak, R. M., Spicuzza, M., and Valley, J. W. (2006) Oxygen isotope evidence for the origin of garnet in the peraluminous South Mountain Batholith, Nova Scotia. Abstracts with Programs - Geological Society of America 38, 113.
This work has yet to come to full fruition, but it does appear that garnets born from peritectic melting reactions in country rock contaminants have oxygen isotope signatures of the country rocks rather than of the granite hosts.

Erdmann, S. and Clarke, D. B. (2006) The South Mountain Batholith – a country-rock contaminated granite. Unpublished Abstract.
In this abstract, we define and make a clear distinction between an orthoxenocryst (originally present in the country rock and now incorporated in a granite) and a paraxenocryst (not originally present in the mineral assemblage of the country rock, but it forms during an incongruent melting reaction when a xenolith is incorporated into the granite magma). The orthoxenocryst is an old crystal made of foreign material; the paraxenocryst is a new crystal made of foreign material. Paraxenocrysts might be mistaken for magmatic phases because they have grown in equilibrium with a melt, but they are composed largely or exclusively of foreign materials.

Erdmann, S. (2006) Country-rock contamination and assimilation in the South Mountain Batholith. PhD Thesis, Dalhousie University, Halifax, Nova Scotia, 212 p. The only comprehensive investigation of contamination of the SMB by the silicate mineral assemblage of the Meguma Supergroup.

Erdmann, S. and Clarke, D. B. (2007) Biotite-, Cordierite-, and Garnet-rich Zones in the South Mountain Batholith, Nova Scotia: are they the Product of Country-rock Assimilation or Fractional Crystallization? Sixth Hutton Symposium on the Origin of Granitic Rocks.
This abstract represents further thinking about the origins of high concentrations of AFM silicates in the SMB. This work reaches completion in Erdmann et al. (2009) below.

Clarke, D. B., Paterson, S. R., Vernon, R. H. (2007) Contaminated Granites. Canadian Mineralogist 45, Part 1, 147 pp.
This reference is a single issue of The Canadian Mineralogist dedicated to examining the wider aspects of contamination and assimilation in granite magmas, including mafic magma mixing.

Clarke, D. B. (2007) Assimilation of xenocrysts in granitic magmas; principles, processes, proxies, and problems. Canadian Mineralogist 45, 5-30.
At last, some generalizations drawn from the many specific cases we had investigated. This paper identifies two pre-assimilation chemical reactions (redox, decomposition) and three assimilation reactions (melting, dissolution, ion exchange) that should account for the assimilation of all xenocrystic (and xenolithic) material in granite magmas.

Clarke, D. B. and Carruzzo, S. (2007) Assimilation of country-rock ilmenite and rutile in the South Mountain Batholith, Nova Scotia, Canada. Canadian Mineralogist 45, 31-42.
The story of the oxide minerals. It is relatively easy to see the textural and chemical distinctions between magmatic and xenocrystic ilmenite and rutile in the SMB.

Erdmann, S., London, D., Morgan, G. B. VI, and Clarke, D. B. (2007) The contamination of granitic magma by metasedimentary country-rock material; an experimental study. Canadian Mineralogist 45, 43-61.
This paper presents a set of experiments on natural Meguma and SMB rocks to clarify the ways in which country rocks can lose their physical and chemical identities in granite magmas.

Clarke, D. B. and Erdmann, S. (2008) Is stoping a volumetrically significant pluton emplacement process?: Comment. Geological Society of America Bulletin 120, 1072-1074.
Granite magmas can create room for themselves by dropping their floors, raising their roofs, forcefully shouldering aside their walls, or passively stoping their envelope. Some workers would like to discount stoping as an emplacement mechanism and, in so doing, would also make contamination insignificant, but field, petrological, and geochemical evidence suggests otherwise. Every cubic metre of stoped and later assimilated rock is a cubic metre of room the magma does not need to create.

Clarke, D. B., Erdmann, S., Samson, H. and Jamieson, R. A. (2009) Contamination of the South Mountain Batholith by Sulfides from the Country Rocks. Canadian Mineralogist (in revision)
Expanding on the work of Samson (2005) above, we now have a detailed understanding of what happens to the country-rock sulfides in the SMB magma. In short, the textural and chemical evidence shows that they concurrently partially melt, ion exchange with the silicate melt, and dissolve in the silicate melt.

Erdmann, S., MacDonald, M. A. and Jamieson, R. A. (2009) Evaluating the origin of garnet, cordierite, and biotite in granitic rocks: A case study from the South Mountain Batholith. Journal of Petrology (in revision)
A refined analysis of the origins of three AFM minerals in the SMB wherein garnet is deemed to be paraxenocrystic, biotite largely magmatic, and cordierite dominantly magmatic.

Jähkel, A. (2010) An investigation of MAX (monazite, apatite, xenotime) contamination in the SMB. Bachelor’s Thesis, University of Potsdam.
This work is due to begin in late July 2009. We anticipate that the established methodology of careful characterization of the country-rock MAX assemblage will enable us to distinguish xenocrysts from magmatic equivalents in the SMB granites.

MacDonald, M. A. and Clarke, D. B. (2010) The petrogenetic significance of mafic porphyries in the SMB.
This work is just beginning, but the mafic porphyries with their abundant xenoliths and xenocrysts may be the most highly contaminated rocks in the SMB, and they will undoubtedly have new insights to reveal.

Peck, W. (201*) Carbon isotope compositions of cordierite from peraluminous granites.
Cordierite encore encore. We have submitted a collection of granites from the SMB and MB to William Peck at Colgate University who plans to analyze the carbon isotope compositions of CO2 in the channels of cordierite crystals. The isotopic signatures of magmatic cordierites may well be different from those of orthoxenocrysts or paraxenocrysts.

Students Supervised

Saskia Erdmann (PhD 2007)
Title: Country-rock Contamination and Assimilation in the South Mountain Batholith

James Sykes (B. Sc. Research Paper 2006)
Title: Physical Processes of Ring Schlieren Formation in the South Mountain Batholith, Nova Scotia.

Hugh Samson (B. Sc. Honours 2005)
Title: Origin of Sulfides in the Contact Granodiorites of the South Mountain Batholith, Nova Scotia

Christopher Hamilton (B. Sc. Honours 2004)
Title: Ice-contact volcanism in the Vilfilsfell Region, southwest Iceland

Sarah Carruzzo, (Ph.D., 2003)
Title:Granite-Hosted Mineral Deposits of the New Ross Area, South Mountain Batholith.
Co-Supervised with: Peter Reynolds

Karla Pelrine (B. Sc. Honours Co-op, 2003)
Title: Chemical analysis of the oxide minerals of the SMB, especially Nb and Ta.

Krista L. McCuish (B.Sc. Honours, 2001)
SCHLIEREN IN THE SOUTH MOUNTAIN BATHOLITH AND PORT MOUTON PLUTON, MEGUMA ZONE, NOVA SCOTIA

Karen M. Sedgwick (B.Sc. Honours Co-op, 1998)
Environmental Effects of the Dunbrack Mine, Musquodoboit Harbour, Nova Scotia
Co-Supervised by: Marcos Zentilli

Raymond Fallon (M.Sc., 1998)
Geochronology of the Port Mouton Pluton, Meguma Zone, Southwest Nova Scotia: A U-Pb and ⁴⁰Ar/³⁹Ar Study.
Co-supervised by:Peter Reynolds

Marcus C. Tate (Ph. D., 1995)
The Relationship Between Late Devonian Mafic Intrusions and Peraluminous Granitoid Generation in the Meguma Lithotectonic Zone, Nova Scotia, Canada