Marble Xenoliths Research Articles

Sr-Nd-Hf-O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide ore deposits in the Emeishan large igneous province

Magma-carbonate interaction and recycled oceanic crust in the mantle source are thought to have played a critical role in the genesis of magmatic Fe-Ti-V oxide ore deposits in the Emeishan mantle plume-related large igneous province in southwestern China. To test these hypotheses, we have carried out a combined study of zircon Hf-O isotopes and whole-rock Sr-Nd isotopes on three representative magmatic Fe-Ti-V oxide ore deposits associated with different types of wall-rock in the province: the Hongge and Taihe deposits with granitoid wall-rocks in most places, and the Panzhihua deposit with marble wall-rocks. Diopside-garnet marble xenoliths are common in the host gabbros of the Taihe deposit. The zircon separates used in this study are all from the mineralized units of the host layered mafic–ultramafic intrusions. The selected zircon grains yield U-Pb isotopic ages of 258.2 ± 2.8 Ma for Hongge intrusion, 263.3 ± 2.2 Ma for Taihe intrusion, and 257.6 ± 2.1 Ma for Panzhihua intrusion. The Hf-O isotopes of the zircon separates are εHf(t) from 3.1 to 4.7 and δ18O from 5.77 to 6.45‰ for Hongge, εHf(t) from 8.3 to 9.8 and δ18O from 4.12 to 4.56‰ for Taihe, and εHf(t) from 4.6 to 6.3 and δ18O from 5.49 to 6.10‰ for Panzhihua. The zircon δ18O values of the Taihe deposit are significantly lower than the mantle zircon values (5.3 ± 0.3‰), whereas those of the Hongge and Panzhihua deposits are higher than the mantle values. The initial 87Sr/86Sr and εNd(t) of the whole rock samples from the deposits are similar, from 0.7047 to 0.7052 and from 2.3 to 3.1, respectively. The observed decoupling of zircon Hf-O isotopes (low δ18O and high εHf(t) values) in the Taihe deposit is most consistent with a high-temperature altered, low δ18O oceanic gabbroic component in the plume source for this deposit. All of the isotope data together show that the parental magmas for these deposits experienced different types of crustal contamination. Contamination with the Precambrian metamorphic country rocks is much more significant in the parental magma for the Hongge deposit than those for the Panzhihua and Taihe deposits. On the other hand, contamination with marble country rocks is more pronounced in the parental magmas for the Panzhihua and Taihe deposits than in the parental magma for the Hongge deposit. An important new finding from this study is that these deposits are not linked to the same component of the mantle plume nor a single type of crustal contamination.

Skarn xenolith record crustal CO2 liberation during Pompeii and Pollena eruptions, Vesuvius volcanic system, central Italy

Limestone assimilation and skarn formation are important processes in magmatic systems emplaced within carbonate-rich crust and can affect the composition of the magma and that of associated volcanic gas. In this study we focus on marble and calc-silicate (skarn) xenoliths from contact reactions between magma and carbonate wall-rock of the Vesuvius volcanic system. We present new elemental and C-O isotope data for marble and skarn xenoliths as well as for igneous rocks collected from the AD 79 (Pompeii) and AD 472 (Pollena) eruptions. The igneous samples have consistently high δ18O values (9.3 to 10.8‰), but low H2O contents (≤1.5%), indicating that magma–crust interaction prior to eruption took place. The marble xenoliths, in turn, record initial decarbonation reactions and fluid-mass exchange in their textures and δ13C and δ18O ranges, while the skarn xenoliths reflect prolonged magma–carbonate interaction and intense contact metamorphism. Skarn-xenoliths record Ca and Mg release from the original carbonate and uptake of Al and Si and span the full δ18O data range from un-metamorphosed carbonate (>18‰) to values typical for Vesuvius magmatic rocks (~7.5‰), which implies that skarn xenoliths comprise carbonate and magmatic components. Textural and chemical evidence suggest that direct carbonate dissolution into the host magmas occurred as well as post-metamorphic skarn recycling, resulting in progressive Ca and Mg liberation from the skarn xenoliths into the magma. Magma–carbonate interaction is an additional source of CO2 during carbonate break-down and assimilation and we calculate the amount of extra volatile components likely liberated by contact metamorphic reactions before and during the investigated eruptions. We find that the extra CO2 added into the volcanic system could have outweighed the magmatic CO2 component by ≥ factor seven and thus likely increased the intensity of both the Pompeii and the Pollena eruptive events.

HOGARTHITE, (Na,K)2CaTi2Si10O26·8H2O, A NEW MEMBER OF THE LEMOYNITE GROUP FROM MONT SAINT-HILAIRE, QUEBEC: CHARACTERIZATION, CRYSTAL-STRUCTURE DETERMINATION, AND ORIGIN

Hogarthite, (Na,K)2CaTi2Si10O26·8H2O, a new mineral of the lemoynite group, was discovered in vugs within metasomatically altered marble xenoliths in the Poudrette quarry, Mont Saint-Hilaire, La-Vallee-du-Richelieu RCM, Monteregie, Quebec, Canada. Crystals are bladed to blocky, average 0.05 × 0.15 × 2 mm in size, and range in color from tan to white to colorless. The mineral develops in dense, radiating crystal aggregates up to 0.5 × 3 mm in size, and is associated with calcite (several generations), quartz, haineaultite, labuntsovite-Mn, lemoynite, chabazite, and gmelinite-Na. Crystals are elongate along [100], flattened on {010} and are bounded by the forms pinacoid {010} (dominant), pinacoid {100} (minor), and pinacoid {001} (minor). The mineral has a white streak, is non-fluorescent under short-, medium-, and long-wave ultraviolet radiation, is translucent, and has a satiny to silky to subvitreous luster. It has a brittle fracture, a perfect {010} cleavage, a hackly to splintery fracture, an estimated hardness of 4, and D calc = 2.40(1) g/cm3. Hogarthite is biaxial (+) with α 1.567(1), β 1.591(1), and γ 1.618(1) with 2 V meas = 87(1)o and 2 V calc = 88(1)o. The optical orientation is X = b , Y ˄ c = 15o (measured in the obtuse angle β), Z = a . A total of 21 analyses, obtained from seven crystals, gave an average (range) of (wt.%): Na2O 2.37 (1.69–2.92), K2O 2.88 (2.61–3.17), CaO 6.00 (5.40–6.31), TiO2 14.44 (13.70–15.83), ZrO2 1.11 (0.48–1.73), Nb2O5 0.78 (0.42–1.24), SiO2 59.27 (57.32–60.64), H2O 14.10 (calc.), total 100.95. The empirical formula (based on 34 anions) is (Na0.78K0.62□0.51Ca0.09)Σ2.00Ca(Ti1.85Zr0.09Nb0.06)Σ2.00Si10.09O26·8H2O, and the simplified formula is (Na,K)2CaTi2Si10O26·8H2O. The presence of (OH) and H2O were confirmed via refinement of the crystal-structure and data from combined FTIR and Raman spectroscopies. The mineral crystallizes in space group C 2/ m with a 10.1839(5), b 15.8244(6), c 9.1327(7) A, β 104.463(2)o, V 1425.1(1) A3, and Z = 2. The strongest six lines on the X-ray powder diffraction pattern [ d in A (I) ( hkl )] are: 8.835 (85) (001), 7.913 (100) (020), 6.849 (70) (![Formula][1] 11), 4.336 (45) (![Formula][2] 31, ![Formula][3] 12), 3.514 (80) (221), 3.426 (55) (![Formula][4] 22, ![Formula][5] 32). The crystal structure, refined to R = 0.049 for 1335 reflections ( F o > 4σ F o), consists of a silicate component, composed of interconnected, non-planar 10-membered rings, arranged into thick slabs and stacked along [001]. These are interleaved with layers of independent TiO6 octahedra, producing a framework of composition [TiSi5O13]2–. Numerous channels within the framework, notably the continuous ones developed by 10-membered silicate rings, are occupied by Na, Ca, and H2O groups. Hogarthite is considered to be a product of late-stage alkaline fluid enriched in SiO2 and TiO2, and forming under conditions of low P at T < 200 oC, possibly through crystallization of a gel. [1]: /embed/mml-math-1.gif [2]: /embed/mml-math-2.gif [3]: /embed/mml-math-3.gif [4]: /embed/mml-math-4.gif [5]: /embed/mml-math-5.gif

UNUSUAL FIBROUS SODIAN TAINIOLITE EPITACTIC ON PHLOGOPITE FROM MARBLE XENOLITHS OF MONT SAINT-HILAIRE, QUEBEC, CANADA

Samples of marble xenoliths, thermally metamorphosed by the igneous rocks of Mont Saint-Hilaire, Quebec, contain idiomorphic plates of phlogopite. These plates were later overgrown and to some extent topotactically replaced by sodian tainiolite, tapering in fragile fibers extending parallel to [100]. The fibers only protrude parallel to [100] of the phlogopite host. Unit-cell parameters of phlogopite and tainiolite, both 1 M polytypes (space group C 2/ m ), are so similar that the phases in the phlogopite –tainiolite intergrowth could not be distinguished by single-crystal X-ray methods. Phlogopite of composition K1.01(Mg1.96Fe0.66Li0.20Mn0.03Ti0.03Al0.04)∑2.92(Si3.28Al0.72)∑4O10[(OH)1.14F0.86]∑2 has the highest Si/Al value of natural samples of phlogopite known to us. The epitactic fibers of tainiolite, of composition K1.01(Mg2.00Fe0.01Li0.59Na0.38)∑2.98(Si3.99Al0.01)∑4O10[F1.79Cl0.01 (OH)0.20]∑2, represent to our knowledge the first example of an extended solid-solution, established by combined electron-microprobe and laser-ablation mass-spectrometry analyses, between tainiolite, K(LiMg2)Si4O10F2, and the recently described mineral shirokshinite, K(NaMg2)Si4O10F2. The latest mineral formed in the observed paragenesis is the zeolite mesolite, accompanied by an unidentified aluminosilicate with Ca/K ≈ 1.

Field Relationships and Geochemical Constraints on the Emplacement of the Jinchuan Intrusion and its Ni-Cu-PGE Sulfide Deposit, Gansu, China

Field mapping and petrological-geochemical investigation of the Jinchuan intrusion in north-central China clarifies how the intrusion was emplaced and provides a new model that explains how its large and rich Ni-Cu-platinoid deposits may have formed. The intrusion was emplaced into high-grade gneisses and marbles along a disconformity at the base of an overlying cover sequence, indicating that it was emplaced as a sill, not a near-vertical dike, as previously proposed. After emplacement the intrusion was rotated to its present orientation and deformed and metamorphosed under greenschist-facies conditions. Relative enrichment of incompatible trace elements coupled with negative U-Th and Nb-Ta anomalies in all samples from the intrusion provide evidence that the parental magma assimilated granitoid rocks in the lower crust. The presence of abundant marble xenoliths, now decarbonatized to diopside-rich skarns, and chemical indices such as high CaO/SiO2, indicate that the magma assimilated carbonate on reaching its present site. This contamination may be linked to the formation of the Ni-Cu platinoid ores. We propose that the assimilation of carbonate-rich fluids increased the oxygen fugacity of the magma and led to the segregation of metal-rich sulfides.

BOBTRAILLITE, (Na,Ca)13Sr11(Zr,Y,Nb)14Si42B6O132(OH)12{middle dot}12H2O, A NEW MINERAL SPECIES FROM MONT SAINT-HILAIRE, QUEBEC: DESCRIPTION, STRUCTURE DETERMINATION AND RELATIONSHIP TO BENITOITE AND WADEITE

Bobtraillite is a new, complex zirconosilicate found in igneous breccias and nepheline syenite pegmatites at the Poudrette quarry, Mont Saint-Hilaire, Quebec. It is associated with a burbankite-group mineral, donnayite-(Y), clinoamphibole, albite, aegirine, pyrrhotite, pyrite, annite, analcime, microcline, a white mica (muscovite?), yellow titanite, clinopyroxene and calcite. Crystals are commonly grey to brown in color, blocky to prismatic, elongate along [001], with a maximum length of 2 mm. It is generally found as isolated single crystals or simple parallel intergrowths with two or three members, rarely in small ( 3 . Bobtraillite is nonpleochroic, uniaxial positive, with ω 1.627(1) and e 1.645(1). Seven analyses made on one crystal gave: Na 2 O 5.62, CaO 1.11, SrO 17.76, BaO 0.40, B 2 O 3 (calc.) 3.38, Y 2 O 3 1.15, SiO 2 40.51, ZrO 2 25.32, HfO 2 0.48, Nb 2 O 5 1.32 and H 2 O (calc.) 5.25, total 102.30 wt.%, corresponding to (Na 11.20 Ca 1.22 ) ∑12.42 (Sr 10.59 Ba 0.16 ) ∑10.75 (Zr 12.69 Y 0.63 Nb 0.61 Hf 0.14 ) ∑14.07 Si 41.64 B 6 O 132 (OH) 12 ·12H 2 O on the basis of 156 anions, or ideally, (Na,Ca) 13 Sr 11 (Zr,Y,Nb) 14 Si 42 B 6 O 132 (OH) 12 ·12H 2 O. The mineral is trigonal, space group P 3 c 1, a 19.720(1), c 9.9788(5) A, V 3360.7(1) A 3 and Z = 1. The strongest six lines on the X-ray powder-diffraction pattern [ d in A(I)( hkl )] are: 2.752(100)(332), 3.13(70)(331), 3.96(51)(212), 3.76(49)(302), 6.46(38)(210), and 5.43(33)(211). The structure of bobtraillite was refined to R = 3.49% and w R 2 = 10.88% for 1575 reflections [ F o > 4σ ( F o )]. Isolated ZrO 6 octahedra are linked by (Si 3 O 9 ) rings to form a pinwheel-like motif similar to that found in wadeite. Additional (Si 3 O 9 ) and [Si 2 BO 7 (OH) 2 ] rings complete a two-dimensional, giant pinwheel motif along [001]. Bonding between three-membered rings and ZrO 6 octahedra along [001] completes the structure in three dimensions. Channels along [001] are occupied by Na, H 2 O and Sr. Bobtraillite shares chemical and crystal-structure features with benitoite, wadeite and catapleiite, and should be considered as a structural hybrid of these minerals. The presence of essential B, Sr, H 2 O and its trigonal symmetry make it unique. We discuss the group classification of minerals based on frameworks containing isolated M O 6 and three-membered rings of tetrahedra. The mineral is paragenetically late, arising from unusual, hydrous fluids enriched in B, Sr, Na and Zr. There are similarities between the fluid resulting in the crystallization of bobtraillite in igneous breccias and that responsible for the assemblages exotic minerals in altered marble xenoliths at Mont Saint-Hilaire. The name of the new species honors Robert (“Bob”) J. Traill, formerly mineralogist at the Geological Survey of Canada, Ottawa.

The Quérigut Complex (Pyrenees, France) revisited by the AMS technique : a syntectonic pluton of the Variscan dextral transpression

Abstract The Variscan Querigut Pluton (eastern Axial Zone, Pyrenees), recently dated at 307 ± 2 Ma, is a classical example for the structural study of granitoids. We present a new structural analysis of this pluton using the powerful technique of magnetic susceptibility anisotropy (AMS). A model of pluton emplacement is proposed on the basis of complementary microstructural analyses allowing the determination of the temperatures of fabric acquisition in the magmatic units, and of the shear sense criteria in the surrounding country rocks. This pluton is constituted by two main units that have intruded metasedimentary rocks where regional metamorphic conditions decrease from southwest to northeast. A well-foliated southern granodioritic unit, rich in Devonian marble xenoliths, is bounded to the south by Cambro-Ordovician metapelites. A weakly foliated northern monzogranitic unit, bounded to the north by Devonian marbles, comprises two sub-types : an outer biotite-monzogranite and an inner biotite-muscovite leucomonzogranite. Abundant basic stocks of variable sizes and lithologies outcrop in the granodioritic unit and in the southern part of the monzogranitic unit. Mean magnetic susceptibility and magnetic foliation maps show a very good agreement with the previous compiled petrographic and structural maps, strengthening the validity of the AMS technique. The northern monzogranitic units display two unevenly distributed structural patterns : (a) a NE-SW-trending pattern of weakly to steeply dipping foliations, dominant in the outer biotite monzogranite, is associated to subhorizontal NE-SW lineations ; and (b) a NW-SE-trending pattern of steeply dipping foliations, dominant in the inner biotite-muscovite monzogranite, is concentrated in NW-SE elongated corridors, associated to subhorizontal NW-SE lineations. In the southern granodioritic unit, foliation patterns follow roughly both the main regional foliation pattern and the pluton boundary, with foliation dips increasing to the south. Subhorizontal NW-SE trending magnetic lineations in the inner parts of this unit, are progressively verticalized toward the southern pluton boundary. A progressive increase in total magnetic anisotropy is observed toward the border of the pluton, correlated with both an increase in solid-state deformation and a decrease of the final temperature of fabric acquisition. These features result from a pluri-kilometric shear zone localized in the western half of the granodioritic unit, decreasing in thickness in its eastern half and along N060oE trending contacts with the country rocks. In the northern monzogranitic unit, one can roughly correlate the magmatic microstructures to the NE-SW trending fabric, and the superimposed subsolidus microstructures to the NW-SE-trending corridors, where rather low-temperature (&amp;lt; 300 oC) fluid-assisted cataclastic microstructures may also appear. The country-rocks, half kilometer away from the pluton border, display the D2 regional Variscan pattern, with subvertical and N110oE-striking foliations and subhorizontal and E-W-trending stretching lineations associated to a dextral shear. Closer to the pluton, the country-rocks are subjected to the pluton influence, particularly along the southern border where a strong flattening is associated to subvertical lineations related to local thrusting of the pluton onto its country rocks. An emplacement model is proposed through the injection of three principal magma batches (granodiorite, biotite-monzogranite and biotite-muscovite monzogranite) that successively and progressively built up the pluton while the whole region was subjected to a dextral and compressive deformation regime, in agreement with AMS results obtained from several other plutons of the Pyrenees.

Fe-bearing trioctahedral micas from Mont Saint-Hilaire, Québec, Canada

AbstractWe document the occurrence of Fe-bearing trioctahedral micas in the Poudrette quarry in the Mont Saint-Hilaire alkaline intrusion, characterize them by microprobe analysis, Mössbauer spectroscopy, X-ray diffraction, and optical measurements, describe their mineral chemistry, and discuss their petrological significance. In the nepheline and sodalite syenite, biotite and annite occur as coarse crystals characterized by low Al content (typically 2 atoms per formula unit, a.f.u.), high Mn content (typically 0.2 to 0.8 a.f.u.) and variable Fe/(Fe+Mg) values from 0.61 to 0.97. In the gabbro, biotite is less Fe-rich, has lower Mn content and high Ti content. Phlogopite is found as small metamorphic crystals in marble xenoliths within the syenite and siderophyllite occurs as large crystals in a metasomatized albitite dyke. Fe3+/Fetot values extend from 0.079 in the siderophyllite to 0.282 in a high-Fe3+ annite. All of the micas except for the phlogopite have high contents of (Fe3+)iv (∼0.13 to 0.45 a.f.u.) despite the high availability of Al in the rocks. We suggest that the high (Fe3+)iv amounts are caused by the high Mn abundance via a local structural mechanism. The great variety of mica encountered at Mont Saint-Hilaire reflects the highly heterogeneous conditions that prevailed during magmatic and postmagmatic crystallization in this intrusion.

Flow Structure and Form of the Deep Creek Stock, Southern Seven Devils Mountains, Idaho

Research Article| January 01, 1973 Flow Structure and Form of the Deep Creek Stock, Southern Seven Devils Mountains, Idaho WILLIS H. WHITE WILLIS H. WHITE 1Henderson Mine, Climax Molybdenum Company, Empire, Colorado 80438 Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIS H. WHITE 1Henderson Mine, Climax Molybdenum Company, Empire, Colorado 80438 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1973) 84 (1): 199–210. https://doi.org/10.1130/0016-7606(1973)84<199:FSAFOT>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WILLIS H. WHITE; Flow Structure and Form of the Deep Creek Stock, Southern Seven Devils Mountains, Idaho. GSA Bulletin 1973;; 84 (1): 199–210. doi: https://doi.org/10.1130/0016-7606(1973)84<199:FSAFOT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Cretaceous Deep Creek stock, a quartz diorite intrusion in the southern Seven Devils Mountains of west-central Idaho, consists of a funnel-shaped western portion and a lobe-shaped eastern prong. The western portion is concentrically zoned with an inward increase in potassium feldspar, quartz, and non-opaque accessories and decrease in biotite, hornblende, and opaque accessories.The orientation of primary platy flow structure and marble xenoliths, as well as the mineral distribution, suggest that the western portion of the stock may extend to depth, but that the eastern prong is a shallow lobe. The platy flow structure is thought to have originated (1) by shear flow alignment of platy minerals parallel to contacts early in the emplacement history of the stock, and (2) by orientation of platy minerals normal to the direction of greatest magmatic pressure during the later stages of intrusion. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.