Metamorphic ultrahigh-pressure tourmaline: Structure, chemistry, and correlations to P-T conditions

Abstract Tourmaline grains extracted from rocks within three ultrahigh-pressure (UHP) metamorphic localities have been subjected to a structurally and chemically detailed analysis to test for any systematic behavior related to temperature and pressure. Dravite from Parigi, Dora Maira, Western Alps (peak P-T conditions ~3.7 GPa, 750 °C), has a structural formula of X(Na0.90Ca0.05K0.01⃞0.04) Y(Mg1.78Al0.99Fe2+0.12Ti4+0.03⃞0.08)Z(Al5.10Mg0.90)(BO3)3TSi6.00O18V(OH)3W[(OH)0.72F0.28]. Dravite from Lago di Cignana, Western Alps, Italy (~2.7-2.9 GPa, 600-630 °C), has a formula of X(Na0.84Ca0.09K0.01⃞0.06)Y(Mg1.64Al0.79Fe2+0.48Mn2+0.06Ti4+0.02Ni0.02Zn0.01)Z(Al5.00Mg1.00)(BO3)3T(Si5.98Al0.02)O18V(OH)3W[(OH)0.65F0.35]. “Oxy-schorl” from the Saxonian Erzgebirge, Germany (≥4.5 GPa, 1000 °C), most likely formed during exhumation at >2.9 GPa, 870 °C, has a formula of X(Na0.86Ca0.02K0.02⃞0.10)Y(Al1.63Fe2+1.23Ti4+0.11Mg0.03Zn0.01) Z(Al5.05Mg0.95)(BO3)3T(Si5.96Al0.04)O18V(OH)3W[O0.81F0.10(OH)0.09]. There is no structural evidence for significant substitution of [4]Si by [4]Al or [4]B in the UHP tourmaline ( distances ~1.620 Å), even in high-temperature tourmaline from the Erzgebirge. This is in contrast to high-T-low-P tourmaline, which typically has significant amounts of [4]Al. There is an excellent positive correlation (r2 = 1.00) between total [6]Al (i.e., YAl + ZAl) and the determined temperature conditions of tourmaline formation from the different localities. Additionally, there is a negative correlation (r2 = 0.97) between F content and the temperature conditions of UHP tourmaline formation and between F and YAl content (r2 = 1.00) that is best explained by the exchange vector YAlO(R2+F)-1. This is consistent with the W site (occupied either by F, O, or OH), being part of the YO6-polyhedron. Hence, the observed Al-Mg disorder between the Y and Z sites is possibly indirectly dependent on the crystallization temperature.

[1]  L. nNeM.RorNrrzr.  Role of natural radiation in tourmaline coloration , 1988 .

[2]  G. Rossman,et al.  Role of natural radiation in tourmaline coloration , 1988 .

[3]  J. Hermann.  Experimental evidence for diamond-facies metamorphism in the Dora-Maira massif , 2003 .

[4]  F. F. Foit,et al.  The structure of vanadium-bearing tourmaline and its implications regarding tourmaline solid solutions , 1979 .

[5]  B. Dutrow,et al.  Tourmaline-rich pseudomorphs in sillimanite zone metapelites: Demarcation of an infiltration front , 1999 .

[6]  L. Reznitskii,et al.  Crystal chemistry of the dravite-chromdravite series , 2004 .

[7]  W. Heinrich,et al.  Synthesis of tourmaline solid solutions in the system Na2O–MgO–Al2O3–SiO2–B2O3–H2O–HCl and the distribution of Na between tourmaline and fluid at 300 to 700 °C and 200 MPa , 2001 .

[8]  K. Kobayashi,et al.  Tourmaline breakdown in a pelitic system: implications for boron cycling through subduction zones , 2007 .

[9]  V. V. Hinsberg,et al.  Boron isotope and light element sector zoning in tourmaline: Implications for the formation of B-isotopic signatures , 2007 .

[10]  D. Henry,et al.  Sector-zoned tourmaline from the cap rock of a salt dome , 1999 .

[11]  W. Maresch,et al.  Pressure-Temperature and Fluid Evolution of Quartzo-Feldspathic Metamorphic Rocks with a Relic High-Pressure, Granulite-Facies History from the Central Erzgebirge (Saxony, Germany) , 1997 .

[12]  Steven R. Bohlen,et al.  The quartz ⇆ coesite transformation: A precise determination and the effects of other components , 1982 .

[13]  John M. Hughes,et al.  V^(3+)-bearing, Mg-rich, strongly disordered olenite from agraphite deposit near Amstall, Lower Austria: A structural, chemical and spectroscopic investigation , 2008 .

[14]  J. A. Thomson.  A rare garnet-tourmaline-sillimanite-biotite-ilmenite-quartz assemblage from the granulite-facies region of south-central Massachusetts , 2006 .

[15]  C. Lengauer,et al.  Tetrahedrally coordinated boron in Al-rich tourmaline and its relationship to the pressure-temperature conditions of formation , 2008 .

[16]  W. Schreyer,et al.  Geochemistry of coesite-bearing “pyrope quartzite” and related rocks from the Dora-Maira Massif, Western Alps , 2008 .

[17]  W. Maresch,et al.  Characterization and geodynamic implications of contrasting metamorphic evolution in juxtaposed high-pressure units of the western Erzgebirge (Saxony, Germany) , 1998 .

[18]  H. Massonne.  A comparison of the evolution of diamondiferous quartz-rich rocks from the Saxonian Erzgebirge and the Kokchetav Massif: are so-called diamondiferous gneisses magmatic rocks? , 2003 .

[19]  R. Coleman,et al.  Geotectonic evolution of diamondiferous paragneisses, Kokchetav Complex, northern Kazakhstan: The geologic enigma of ultrahigh‐pressure crustal rocks within a Paleozoic foldbelt , 1995 .

[20]  V. V. Hinsberg,et al.  Intersector element partitioning in tourmaline: a potentially powerful single crystal thermometer , 2006, Contributions to Mineralogy and Petrology.

[21]  B. Dutrow,et al.  Tourmaline in meta-evaporites and highly magnesian rocks: perspectives from Namibian tourmalinites , 2008 .

[22]  John M. Hughes,et al.  TETRAHEDRALLY COORDINATED BORON IN A TOURMALINE: BORON-RICH OLENITE FROM STOFFHÜTTE, KORALPE, AUSTRIA , 2000 .

[23]  R. Kretz.  Symbols for rock-forming minerals , 1983 .

[24]  John M. Hughes,et al.  Mn-rich tourmaline from Austria: structure, chemistry, optical spectra, and relations to synthetic solid solutions , 2004 .

[25]  R. Howie,et al.  An Introduction to the Rock-Forming Minerals , 1966 .

[26]  S. Lucchesi,et al.  Crystal chemistry of the schorl-dravite series , 2004 .

[27]  D. Mukhopadhyay,et al.  Tourmaline-bearing rocks in the Singhbhum shear zone, eastern India: Evidence of boron infiltration during regional metamorphism , 2005 .

[28]  John M. Hughes,et al.  DISORDERED Mg-BEARING OLENITE FROM A GRANITIC PEGMATITE AT GOSLARN, AUSTRIA: A CHEMICAL, STRUCTURAL, AND INFRARED SPECTROSCOPIC STUDY , 2003 .

[29]  F. Bundy.  The P, T phase and reaction diagram for elemental carbon, 1979 , 1980 .

[30]  John M. Hughes,et al.  POLYHEDRON DISTORTIONS IN TOURMALINE , 2002 .

[31]  E. Schmädicke,et al.  Unusual exsolution phenomena in omphacite and partial replacement of phengite by phlogopite + kyanite in an eclogite from the Erzgebirge , 2000 .

[32]  Michael Wiedenbeck,et al.  Chemical and boron-isotope variations in tourmalines from an S-type granite and its source rocks: the Erongo granite and tourmalinites in the Damara Belt, Namibia , 2007 .

[33]  J. Grice,et al.  Ordering of Fe and Mg in the tourmaline crystal structure: The correct formula Sample: Dravite 43873 , 1993 .

[34]  J. Slack.  Tourmaline associations with hydrothermal ore deposits , 1996 .

[35]  H. Marschall,et al.  On the occurrence and boron isotopic composition of tourmaline in (ultra)high-pressure metamorphic rocks , 2009, Journal of the Geological Society.

[36]  John M. Hughes,et al.  Mn-bearing “oxy-rossmanite” with tetrahedrally coordinated Al and B from Austria: Structure, chemistry, and infrared and optical spectroscopic study , 2005 .

[37]  C. Lengauer,et al.  Substitution mechanism in tourmalines of the "fluor-elbaite"-rossmanite series from Wolkenburg, Saxony, Germany , 2009 .

[38]  Frank C. Hawthorne,et al.  Classification of the minerals of the tourmaline group , 1999 .

[39]  H. Massonne,et al.  Dating of zircon and monazite from diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge – hints at burial and exhumation velocities , 2007, Mineralogical Magazine.

[40]  E. Tillmanns,et al.  The equivalent isotropic displacement factor , 1988 .

[41]  A. Ertl.  Investigations on Olenite with Excess Boron fromthe Koralpe, Styria, Austria , 1997 .

[42]  John M. Hughes,et al.  Metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, associated with omphacite, from Syros, Greece: chemistry and structure , 2004 .

[43]  Barbara L. Dutrow,et al.  COMPLEXLY ZONED FIBROUS TOURMALINE, CRUZEIRO MINE, MINAS GERAIS, BRAZIL: A RECORD OF EVOLVING MAGMATIC AND HYDROTHERMAL FLUIDS , 2000 .

[44]  E. Nakamura,et al.  Record in metamorphic tourmalines of subduction-zone devolatilization and boron cycling , 2001 .

[45]  Thomas Reinecke,et al.  Very-high-pressure metamorphism and uplift of coesite-bearing metasediments from the Zermatt-Saas zone, Western Alps , 1991 .

[46]  T. Reinecke.  Prograde high- to ultrahigh-pressure metamorphism and exhumation of oceanic sediments at Lago di Cignana, Zermatt-Saas Zone, western Alps , 1998 .

[47]  D. Henry,et al.  Tourmaline as a petrogenetic indicator mineral - An example from the staurolite-grade metapelites of NW Maine , 1985 .

[48]  W. Schreyer,et al.  Experimental studies on borosilicates and selected borates , 1996 .

[49]  M. Dyar,et al.  Inclusive chemical characterization of tourmaline: Mössbauer study of Fe valence and site occupancy , 1998 .

[50]  F. Hawthorne,et al.  The crystal chemistry of Si Al substitution in tourmaline , 1995 .

[51]  John M. Hughes,et al.  Structural and chemical response to varying [4]B content in zoned Fe-bearing olenite from Koralpe, Austria , 2004 .

[52]  G. Van den Bleeken,et al.  Epigenetic to low-grade tourmaline in the Gdoumont metaconglomerates (Belgium): A sensitive probe of its chemical environment of formation , 2007 .

[53]  John M. Hughes,et al.  Tetrahedrally coordinated boron in tourmalines from the liddicoatite-elbaite series from Madagascar: Structure, chemistry, and infrared spectroscopic studies , 2006 .

[54]  P. Burns,et al.  Reassignment of cation site occupancies in tourmaline: Al-Mg disorder in the crystal structure of dravite , 1993 .

[55]  Barbara L. Dutrow,et al.  Tourmaline in a low grade clastic metasedimentary rock: an example of the petrogenetic potential of tourmaline , 1992 .

[56]  C. Chopin.  Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences , 1984 .

[57]  G. Donnay,et al.  Refinement of the crystal structure of elbaite and the mechanism of tourmaline solid solution , 1972 .

[58]  P. Burns,et al.  The crystal chemistry of manganese-bearing elbaite , 1994 .

[59]  W. Schreyer,et al.  The pyrope-coesite rocks and their country rocks at Parigi, Dora Maira Massif, Western Alps: detailed petrography, mineral chemistry and PT-path , 1991 .

[60]  Tetsuo Kawakami,et al.  Tourmaline breakdown in the migmatite zone of the Ryoke metamorphic belt, SW Japan , 2001 .