Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOsciences <![CDATA[ Foreword to the special issue arising from the international conference “Tourmaline 2017” ]]> Cempírek J, Novák M; Vol. 63, issue 2, pages 75 - 76
Twenty years ago (June 1997), the first Tourmaline Conference was organized by Milan Novák (Moravian Museum, Brno, Czech Republic) and Frank Hawthorne (University of Manitoba, Winnipeg, Canada). This meeting brought together an international group of scientists to discuss tourmaline research and to advance tourmaline science, and this led to a host of fruitful collaborations. Results of this conference were published in special issues of the European Journal of Mineralogy and Journal of the Czech Geological Society. Over the years, this meeting attained mythical status among tourmaline researchers, and a second edition was long overdue.
In June 2017, at the 20th anniversary of the first conference, Jan Cempírek and Milan Novák (Masaryk University) reconvened 61 scientists from 17 countries at the same location near Nové Město na Moravě (Czech Republic) to assess progress in tourmaline research, to discuss new challenges, and to catalyze community efforts for advancing tourmaline science.
A series of eight keynote lectures over the three-day conference highlighted the state-of-affairs, challenges, and future directions for tourmaline research in mineralogy, petrology, and geochemistry. These were interspersed with numerous contributed presentations and posters. With the experience of having attended both meetings, Darrell Henry (Louisiana State University, USA) began with a historical perspective on the issues leading to the 1997 conference and a broad overview of progress since that time. Ferdinando Bosi (Sapienza University of Rome, Italy) reviewed the complexities of the tourmaline structure and chemistry, as well as the advances in structure determination that have highlighted the importance of short-range order. Andreas Ertl (University of Vienna, Austria) focused on tourmalines with tetrahedral boron, a finding first reported at the 1997 meeting. Federico Pezzotta (Natural History Museum of Milan, Italy) presented tourmaline in gem pegmatites. Eleanor Berryman (GFZ Potsdam, Germany) discussed experimental work on tourmaline that has allowed quantitative correlations to be made between select major elements in tourmaline and fluid chemistry. Barbara Dutrow (Louisiana State University, USA) highlighted the utility of tourmaline as an indicator of the fluid phase, relating, for example, some tourmaline species (e.g. oxy-dravite/povondraite) to salinity trends. Horst Marschall (Goethe University, Germany) provided an overview of tourmaline isotopic systematics where “no element is left behind” and discussed the need for more studies on isotopic systems. Vincent van Hinsberg (McGill University, Canada) presented new work on trace elements in tourmaline, demonstrated the challenges in obtaining and interpreting such data, and showed the potential for carefully collected data. Robert Trumbull (GFZ German Research Centre for Geosciences, Germany) showed that tourmaline has many applications when it comes to interpreting the genesis of ore systems, and he focused on B isotopic studies. One of the key outcomes of the meeting was the recognition that tourmaline’s unique structure has a complex control on its composition: both short- and long-range element order determine what major and trace elements can be accommodated. Understanding and quantifying this control holds great promise to expand tourmaline’s use as an indicator mineral.
A field trip to eight classic tourmaline localities in the eastern part of the Bohemian Massif followed the conference, led by Milan Novák and Jan Cempírek with Petr Gadas, Radek Škoda, and Renata Čopjaková. Outcrops permitted all of the attendees to collect tourmalines of variable origins: from abyssal pegmatites, through orthogneisses, metacarbonates and granitic pegmatites (LCT as well as NYF family) to nodular granites. A field guide (Buriánek et al. 2017) supplemented overviews given by tourmaline researchers at each locality.
One of the aims of the Tourmaline 2017 conference was promoting experience transfer to students; the 23 students from 10 countries who joined the conference presented results from a large variety of interesting studies, pushing the boundaries of tourmaline research further into unknown areas. This special issue, which presents ten papers on various topics, also includes several remarkable student papers.
The first article by Darrell Henry and Barbara Dutrow brings a review of tourmaline research history. The increase in number of publications, especially in last 20 years, is remarkable and shows how important group of minerals tourmaline became.
The second contribution by Barbara Dutrow and Darrell Henry reviews the behavior of tourmaline as a monitor of hydrothermal fluid composition. Tourmaline clearly became very useful in exploration and petrogenetic research of multiple (e.g., porphyry, VMS, orogenic gold or U, Cu, Mo) types of ore deposits and hydrothermal environment in general.
The third and fourth papers by Zbyněk Buřival and Milan Novák, and Emily Scribner et al. deal with metasomatic processes and tourmaline formed by replacement of garnet and amphiboles. In the latter case, unusually Ca,Ti-rich tourmalines formed, possibly with high Fe3+ contents, in calc-alkaline lamprophyre dikes.
The fifth article by Peter Bačík uses site-occupancy unconstrained approach to assess the structural response of tourmaline octahedral sites to compositional changes in simple Fe-Mg-Al-Li tourmalines. Besides the bond-valence relations, the study emphasized effects of Jahn-Teller distortion that can be the decisive factor in cation occupancy in tourmaline.
Two subsequent papers focus on spectroscopic properties of tourmaline - the team led by Simone F. Silva discusses optical (NIR-vis-UV) spectra of several types of colored tourmalines from Brazil, whereas Elizabeth Lévy et al. used XANES for determination of the Fe3+/Fe2+ ratio in schorlitic tourmalines.
Tamás Spránitz and colleagues present the first comprehensive petrological study of tourmaline-rich rocks from Sopron area in north-western Hungary. Using tourmaline, they successfully traced a large part of the magmatic and metamorphic history of the area.
The two final contributions by Shoshauna Farnsworth-Pinkerton et al. and Oleg Vereshchagin et al. deal with tourmaline applications in provenance of sedimentary rocks using Laser-Induced Breakdown Spectroscopy (LIBS) and multi-mineral approach. Clearly, tourmaline can provide useful information on provenance of sedimentary rocks; however, Vereshchagin et al. conclusively showed that multi-mineral approach combined with detrital zircon dating should be ideally employed, as many rock types lack tourmaline. ]]> Editorial
<![CDATA[ Tourmaline studies through time: contributions to scientific advancements ]]> Henry DJ, Dutrow BL; Vol. 63, issue 2, pages 77 - 98
Tourmaline studies have been an integral part of science and scientific exploration for centuries and continue to flourish today. In the 19th century, the curious pyroelectric and piezoelectric properties of this mineral attracted the attention of scientists who considered tourmaline central to a grand unification of the theories of heat, electricity and magnetism. The common occurrence of tourmaline in granites and granitic pegmatites was widely known at that time, but, subsequently, tourmaline was discovered in a great range of igneous, metamorphic and sedimentary rocks and a variety of ore deposits, including hydrothermal systems. The chemical complexity of this mineral became more fully established and “appreciated” by the end of the 19th century.
In the early- and mid-20th century, tourmaline studies greatly expanded as a consequence of the (1) exploration of wider ranges of geological settings, (2) development of instrumentation to characterize the chemical and physical properties of minerals and (3) the applications that derived from these studies. In clastic sedimentary rocks, tourmaline was identified as one of the most important heavy minerals and became a means to estimate maturity of the clastic sediment, to determine provenance and to make stratigraphic correlations. The crystallography of tourmaline was more fully understood and the overall structure and general structural formula was known by the 1960-1970’s. Applications of tourmaline relied originally on its piezoelectric properties that became increasingly important during the 20th century. One application, developed after World War I, was the detection and measurement of conventional and atomic explosion pressures based on tourmaline’s piezoelectric properties.
Tourmaline studies have expanded in breadth and greatly increased in number since 1977, when micro-analytical and crystallographic/spectroscopic instrumentation became widely available. Petrologically, tourmaline has become a valuable petrogenetic indicator mineral in rocks and sediments due to its occurrence in most rock types, its extreme P-T range of stability, from the near surface to the deepest levels of the crust, its capacity to attain a chemical signature during the evolution of the rock in which it is formed, its ability to retain that chemical imprint, and its capability to provide specific information on the time, temperature and fluid history of its host rock. More recent studies have greatly expanded the conceptual framework of its internal structure and have dramatically increased the number of tourmaline species from 4 to 33. The future of tourmaline studies is promising with many new and exciting possibilities that will continue to influence scientific inquiry well into the future. ]]> Original paper
<![CDATA[ Tourmaline compositions and textures: reflections of the fluid phase ]]> Dutrow BL, Henry DJ; Vol. 63, issue 2, pages 99 - 110
Tourmaline uniquely records evidence of its geologic history in its composition and, if properly decoded, provides insight into the geologic environment of formation. Recent studies suggest that tourmaline not only retains chemical information on the host-rock environment, but also provides signatures on the fluid phase with which it interacted. Such signatures are embedded in its major- and minor-element compositions as well as in its isotopes. Some of these elemental signatures are qualitative, while others provide quantitative evaluation of the evolving fluid-phase compositions. Chemical fingerprints of interacting fluids are found as compositional variations in each of the tourmaline structural sites. Boron, a fluid-mobile element, can be used to monitor local release of boron from the breakdown of pre-existing B-bearing minerals or it can provide evidence for infiltration of external fluids. The exchange of Fe3+ for Al in deprotonated tourmalines along the oxy-dravite to povondraite join (O-P trend) is generally consistent with tourmaline formation coexisting with fluids in an oxidizing, saline environment. Fluorine can serve as a marker for F-bearing aqueous fluids, but the crystallochemical constraints associated with vacancies on the X site and the resulting increase in local charge on the Y site must be considered. In some cases, quantitative information derived from Na, Ca, K, and vacancies allow calculation of the compositions of select components in the co-existing fluids. While isotopes provide valuable insights into fluid-related processes, their signatures are beyond the scope considered here.
Insights into geological processes in fluid-rich environments can be inferred by the presence of tourmaline as well as by tourmaline compositions. For example, tourmaline forming along shear zones suggests that enhanced permeability accompanied infiltration of Na and B-bearing fluids. Oscillatory-zoned tourmaline from geothermal systems captures chemical, thermal, and mechanical feedback from non-linear fluid behavior at critical conditions in the H2O-system. In other cases, textural, morphological and chemical changes in tourmaline mark the transition from magmatic-to- hydrothermal conditions during the evolution of igneous systems. Consequently, signatures in tourmaline can be indicators of the fluid-phase composition and, in some cases, provide quantitative estimates of ion concentrations in the fluid in addition to its host rock environment. Capturing these chemical signals of fluids preserved in tourmaline extends its petrogenetic utility. ]]> Original paper
<![CDATA[ Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids ]]> Buřival Z, Novák M; Vol. 63, issue 2, pages 111 - 122
Secondary blue tourmaline (schorl to Fe-rich fluor-elbaite to very rare Fe-rich fluor-liddicoatite) with quartz partially replace spessartine-almandine garnet and albite in elbaite-subtype pegmatites cutting pyroxene gneisses and calcite or dolomite marbles (at Tamponilapa and Tsarafara-Nord, Sahatany Valley, Madagascar) and paragneisses (at Ctidružice, Moldanubian Zone, Czech Republic). Only garnet from the albite adjacent to an unit with Li-bearing minerals (Li-micas, Li-tourmalines) underwent this alteration, whereas associated primary tourmaline (schorl to Mg-bearing schorl) remained unaltered. Textural relations and chemical composition of the individual minerals suggest the following equation of replacement for averaged and simplified (Ca-free) compositions of garnet and secondary tourmaline from Tsarafara:
25 NaAlSi3O8 + 2 (Mn2Fe1)Al2Si3O12 + 12 H3BO3 + 4 LiF → 4 (Na0.75 0.25)(Al1.25Li1.00Fe0.50Mn0.25)Al6(Si6O18)(BO3)3(OH)3F + 46 SiO2 + 11 Na2SiO3 + 3 MnO + 12 H2O
Elevated contents of Al, Fe, Na and Mn in secondary tourmaline were likely sourced from the replaced garnet and albite, whereas the residual fluids supplied B, F, Li, and H2O. Garnet and associated primary tourmaline are rather Mg-rich but the secondary tourmaline is typically Mg-free. The contents of Ca are high in both tourmaline generations, but the secondary one is occasionally even more enriched compared to the associated primary tourmaline. Such a behavior of Mg and Ca suggests that no Mg was externally supplied during primary crystallization of primary tourmaline from the moment when pegmatite melt was sealed off the host rock. Negligible to none concentrations of Mg in secondary tourmaline show that the pegmatite system was closed to the host rocks during the hydrothermal alteration producing the secondary tourmaline generation. Evident absence of external Mg-contamination from host Ca, Mg-rich rock rules out also any contamination by Ca. High contents of Ca in primary tourmaline and garnet are related to originally Ca-enriched pegmatite melt contaminated before emplacement. ]]> Original paper
<![CDATA[ Mineralogy of Ti-bearing, Al-deficient tourmaline assemblages associated with lamprophyre dikes near the O’Grady Batholith, Northwest Territories, Canada ]]> Scribner ED, Groat LA, Cempírek J; Vol. 63, issue 2, pages 123 - 135
Calc-alkaline lamprophyre dikes are hosted by tourmalinized metasedimentary rocks in the Northwest Territories, Canada. Some of these lamprophyre dikes are cross-cut by aplite and pegmatite dikes, as well as tourmaline-bearing quartz veins that were all derived from the nearby granitic O’Grady Batholith.
The lamprophyre dikes are composed of actinolite to magnesio-hornblende, plagioclase, K-feldspar and quartz with minor phlogopite (up to 4.13 wt. % TiO2), titanite, apatite, pyrite, allanite-(Ce), and zircon. A zone near the margin of one of the dikes has been altered to tourmaline associated with actinolite to magnesio-hornblende, clinochlore, titanite and quartz, with minor clinopyroxene and apatite. Two generations of tourmaline are recognized: Tur I occurs in quartz at the margin of the dike and Tur II forms a massive aggregate with common inclusions of other minerals in an altered lamprophyre zone near the margin of the dike. The vast majority of the analyzed tourmaline is Al-deficient, with less than 6 apfu Al at the Z site (on average 5.691 apfu in Tur I and 5.601 apfu in Tur II). Tur I is mostly dravite with uvite, plus minor feruvite and fluor-uvite, while Tur II contains a greater proportion uvite, feruvite, and fluor-uvite. The most evolved tourmaline compositions observed are feruvite with up to 2.17 wt. % TiO2, and fluor-uvite with up to 0.84 wt. % F. The tourmaline composition reflects the unique geochemical environment in which it crystallized; from Tur I to Tur II, tourmaline becomes richer in Ca-, Fe-, and Ti, presumably due to the reaction of boron-bearing fluids with the Al-poor, Ca-, Mg-Fe-, and Ti-bearing minerals in the lamprophyre dike. The high F contents of some tourmaline species suggest that it crystallized from fluids derived from the aplite and pegmatite dikes. ]]> Original paper
<![CDATA[ The crystal-chemical autopsy of octahedral sites in Na-dominant tourmalines: octahedral metrics model unconstrained by the Y,Z-site disorder assignment ]]> Bačík P; Vol. 63, issue 2, pages 137 - 154
The structure of tourmaline-supergroup minerals includes two types of octahedral sites: the ZO6 octahedron is smaller and more distorted than the YO6 octahedron. The octahedral sites metrics were studied and their dependency on the chemical composition unconstrained by Y,Z-site disorder assignment. Published chemical and structural data were collected from American Mineralogist Crystal Structure Database for tourmaline samples belonging to dravite-schorl, schorl-elbaite (including tsilaisites) and schorl (±dravite)-olenite series. Correlation analysis of this dataset provided the evidence of cation distribution between sites - Al and Mg are disordered between Z and Y sites, while Fe (mostly ferrous), Li and Mn strongly prefer Y site. Irregular cation distribution results in the variable metrics of both octahedra in tourmalines. It is the function of well-balanced relations between cations at octahedral and neighbouring sites based on bond-valence variations due to different ionic charges. Considering Z and Y cations, there is a dependence of the cation charge difference and the octahedral metrics. The most pronounced irregularity of both octahedra was observed in elbaite samples with the largest charge difference between Li and Al. In contrast, “buergerite” samples with trivalent Fe and Al at both octahedral sites have both octahedra almost isometric. Schorl and dravite samples display an increasing metric irregularity related to the Al and Mg content; increase in Mg reduces irregularity because Mg is distributed between both octahedral sites balancing charge difference. In contrast, Fe-rich and Al-rich schorl samples display larger irregularity which may result from selective incorporation of Fe2+ to the Y site. In olenite samples, the irregularity of both octahedra decreases with an increasing Al content. These variations are related to the shared edge of ZO6 and YO6 octahedra including both O3 and O6 site where bonds of both anions are balancing bond-valence requirements of the stable electroneutral structure. In addition to the bond-valence relations, effects of the internal geometry of atomic shells should be also considered, i.e. Jahn-Teller distortion that can be decisive factor in cation occupancy. Especially Fe2+ can strongly prefer YO6 octahedron whose prolonged tetragonal dipyramidal geometry is more favourable for Fe2+ in (t2g)4(eg)2 configuration. ]]> Original paper
<![CDATA[ Chemical and spectroscopic characterization of tourmalines from the Mata Azul pegmatitic field, Central Brazil ]]> da Silva FS, Moura MA, Queiroz Hde A, Ardisson JD; Vol. 63, issue 2, pages 155 - 165
This study characterizes natural black, blue, dark green, light green and pink tourmalines from granitic pegmatites of the Mata Azul Pegmatitic Field in central Brazil. The differences were assessed by applying electron-microprobe analysis as well as Mössbauer and optical spectroscopies. Mineral chemistry data show an increasing Mn/(Mn + Fe) atomic ratio as follows: black (0.01-0.02), blue (0.04-0.05), dark green (0.09-0.21), light green (0.33-0.42) and pink (0.68-1.00).
The Mössbauer spectroscopy results show the presence of Fe2+ (doublets with isomer shift (δ): 1.04-1.15 mm/s) for the black, blue, light green and dark green tourmalines. Fe2+ is found in three different environments that are identified by quadrupole splitting (Δ) of 2.38-2.49 mm/s for the first, Δ = 2.13-2.34 mm/s for the second, and Δ = 1.54-1.71 mm/s for the third. The black sample spectrum has an additional fourth doublet (δ = 0.78 mm/s, Δ = 1.22 mm/s) that is assigned to an electron delocalization between Fe2+ and Fe3+.
In the studied samples, the black color results most likely from high absorbance in all the visible spectra caused by Fe2+-Fe3+ intervalence charge transfer (IVCT) (780 nm), Fe2+ d-d transitions (730 nm, 670 nm), Fe2+-Ti4+ IVCT (430 nm) and transitions related to Mn cations (550 nm). Blue is differentiated from green colors by a higher absorbance in the 730 nm region (Fe2+ d-d transitions), and a higher FeO content, as well as a lower absorbance in the 430 nm region and a lower TiO2 content. The green colors are associated with the absorption bands at 730 nm (Fe2+ d-d transitions) and 430 nm (Fe2+-Ti4+ IVCT). The light green color exhibited a lower intensity of these bands compared to that of the dark green color, and an additional band at 320 nm (Mn2+-Ti4+ IVCT). The pink color results from the high degree of Mn-Fe fractionation but it was not possible to assure the oxidation states of the Mn cations. ]]> Original paper
<![CDATA[ Determination of ferrous-ferric iron contents in tourmaline using synchrotron-based XANES ]]> Levy EA, Henry DJ, Roy A, Dutrow BL; Vol. 63, issue 2, pages 167 - 174
The complex geochemistry of tourmaline makes it an important tool in determining its formational environment. Typically, tourmaline chemistry is analyzed through electron-probe microanalysis (EPMA), but this analytical tool cannot determine directly the oxidation states of transition elements such as Fe (Fe2+, Fe3+). Direct quantitative measurement of these cations is important in minerals to acquire a more complete chemical characterization and informative structural formula. Synchrotron-based X-ray Absorption Near Edge Spectroscopy (XANES) is a method to directly measure Fe2+ and Fe3+ in minerals, including tourmaline. This method utilizes advances in software and detector technology to significantly decrease data processing time and errors.
Three tourmaline samples, dravite, povondraite, and oxy-schorl, analyzed by combining XANES and EPMA data, exhibit distinct ferrous-ferric contents using the pre-edge and absorption edge methods. These analyses reveal, respectively: 99.62-100 wt. % Fe2+ in dravite, 12.5-20.00 wt. % Fe2+ vs. 87.48-100 wt. % Fe3+ in povondraite, and 63.03wt. % Fe2+ vs. 36.98-36.41 wt. % Fe3+ in schorl. Information on the oxidation states of Fe results in enhanced charge-balanced constraints that allow improved estimation of the H contents in the tourmaline and a more accurate designation of the structural formula and classification of tourmaline species. Thus, XANES is a viable technique to obtain oxidation states of transition elements in tourmaline. ]]> Original paper
<![CDATA[ Magmatic and metamorphic evolution of tourmaline-rich rocks of the Sopron area, Eastern Alps ]]> Spránitz T, Józsa S, Kovács Z, Váczi B, Török K; Vol. 63, issue 2, pages 175 - 191
Tourmaline-rich pegmatitic orthogneisses, tourmalinites, kyanite-chlorite-muscovite schists and quartzites crosscut by subordinate quartz-tourmaline veins and layers were newly described from the Sopron area, Western Hungary.
The orthogneisses mainly consist of quartz, plagioclase, tourmaline, garnet and white mica. In smaller amounts K-feldspar, beryl, Mg-rich chlorite, kyanite, lazulite, florencite, monazite and apatite also are present. Magmatic cores and two generations of metamorphic tourmaline (Fe-rich and Mg-rich) were distinguished.
Tourmaline in tourmalinites is generally large (several cm), deformed, contains chlorite inclusions and shows oscillatory zoning or polygonal fabric. Large tourmaline crystals often contain dark brown mica-shaped relic areas with higher amount of Ti and Fe than the adjacent parts, interpreted as relics of micas from the protolith. Besides tourmaline, quartz, white mica, plagioclase, apatite, garnet, rutile, ilmenite, scheelite, zircon and monazite are also present in the tourmalinites.
Deformed tourmaline-quartz bands and veins occur in kyanite-chlorite-muscovite schists and quartzites. Euhedral, zoned and deformed schorl-dravite, is accompanied with kyanite, Mg-chlorite (leuchtenbergite), rutile muscovite and sillimanite. Narrow colorless tourmaline rims enriched exclusively in Mg (FeO < 1 wt. %) can be identified.
Coarse-grained orthogneisses with a significant amount of primary tourmaline-beryl assemblage indicates a fluid-rich, B-Be-bearing environment during the final crystallization of the Variscan peraluminous leucogranite. The formation of tourmalinites can be explained by the related boron metasomatism. Phengitic white mica rims and calcic garnet rims in orthogneisses and tourmalinites indicate high-pressure Alpine metamorphic overprint. The presence of REE-rich phosphate mineralisation and leuchtenbergite in the orthogneisses imply that high salinity fluids metasomatized the orthogneisses along the pre-existing shear zones after the Alpine metamorphic peak. Tourmaline grains in kyanite-bearing quartzites and schists may have originated from a micaschist that underwent a strong Mg-metasomatism during the formation of leucophyllites described from the area. ]]> Original paper
<![CDATA[ Provenance of detrital tourmalines from Proterozoic metasedimentary rocks in the Picuris Mountains, New Mexico, using Laser-Induced Breakdown Spectroscopy ]]> Farnsworth-Pinkerton S, McMillan NJ, Dutrow BL, Henry DJ; Vol. 63, issue 2, pages 193 - 198
Tourmaline is a useful mineral for determining provenance of sediments. Here, detrital tourmaline has been used to evaluate provenance for the Rinconada and Piedra Lumbre formations in the Copper Hill Anticline, Picuris Mountains, New Mexico, USA to assess the existence of the proposed Mesoproterozoic Picuris Orogeny. This orogeny has been proposed by other authors based on the presence of 1600-1475 Ma detrital zircons in the Piedra Lumbre Formation of the Hondo Group and Yavapai age (1780-1700 Ma) detrital zircons in units underlying the Piedra Lumbre Formation, including the Rinconada Formation.
Optically distinct detrital cores of tourmaline grains from the Rinconada and Piedra Lumbre formations were analyzed using Laser-Induced Breakdown Spectroscopy (LIBS) to establish likely lithologic sources. A total of 209 LIBS spectra of detrital grains were collected from the Rinconada Formation, 50 of which were tourmaline. Based on multivariate analysis of these 50 tourmalines, 24 are most likely from pelitic metamorphic rocks, four from calcareous metamorphic rocks, eight from Li-poor pegmatites and silicic igneous rocks, and 14 from hydrothermal rocks. In contrast, none of the 3274 LIBS spectra collected from the Piedra Lumbre Formation were from tourmaline.
Source regions for the Rinconada and Piedra Lumbre formations are interpreted to be different due to the presence of tourmaline in the Rinconada Formation and its absence in the Piedra Lumbre Formation. Based on detrital tourmaline data, evidence for a change in provenance supports the proposed Picuris Orogeny. ]]> Original paper
<![CDATA[ Provenance of Jurassic-Cretaceous siliciclastic rocks from the northern Siberian Craton: an integrated heavy mineral study ]]> Vereshchagin OS, Khudoley AK, Ershova VB, Prokopiev AV, Schneider GV; Vol. 63, issue 2, pages 199 - 213
The U-Pb ages of detrital zircons and the chemical compositions of detrital garnets and tourmalines from Jurassic-Cretaceous sedimentary rocks of the northern part of the Priverkhoyansk Foreland Basin, the central part of the Yenisey-Khatanga Depression, and the northern part of the Taimyr-Severnaya Zemlya Fold and Thrust Belt were used for a provenance study. Detrital zircons display two age populations, dominated by Late Paleozoic and Paleoproterozoic-Archean zircons, respectively. The first population was recognized in all samples, whereas the second is restricted to Cretaceous samples, suggesting that erosion of the Siberian Craton basement was the main source of clastic sediments only during the Cretaceous. The chemical compositions of the garnets also indicate several sources of detrital material, which changed with time. There are significant differences in the composition of Jurassic (grossular-almandine) and Cretaceous (mainly pyrope) garnets. The pyrope association is characteristic of the high-grade metamorphic rocks of the Siberian Craton, which correlates well with our zircon data. The chemical composition of tourmaline grains varies widely and does not show significant differences between samples of different ages, therefore could not be used to discriminate between different provenance areas in this study. ]]> Original paper