Magmatic Petrology

Dear researchers, Geoscience and the progress of technology can be put to the service of the environment for the improvement of human living conditions. In this context, the Laboratory of Geodynamics and Natural Resources (LGRN), Department of Geology, The Second Edition of Doctoral Days (2EJD), to be held on January 14 & 15, 2019 at the Faculty of Sciences Dhar El Mahraz, Sidi University Mohamed Ben Abdellah, Fez, Morocco. Research Ph.D. students will then have the opportunity to disseminate their research and share their experiences with other researchers. This edition will cover a wide range of topics in the fields of Geoscience and Natural Resources. Researchers who want to participate in the event Email: lgrn.doctoriales@gmail.com We look forward to meeting you at the Faculty of Sciences Dhar El Mahraz.

Tin-tungsten-associated granites occur widely in the Dawei region of the Southeast Asian tin belt. In this contribution, we present a detailed study of zircon U–Pb geochronology and whole-rock and zircon elemental
geochemistry for the Wagone and Hermyingyi granites in southern Myanmar, with the aim of determining their
petrogenesis, mineralization associations, and tectonic setting. These granitic rocks, which belong to the high-K
calc-alkaline series A2-type granites, are characterized by high concentrations of SiO2 (75.2–82.5%), Rb
(264–927 ppm), Th (18.4–58.3 ppm), U (10.4–18.3 ppm), and Y (33.5–212 ppm), but low contents of TFeO
(0.57–3.45%), CaO (0.23–0.86%), MgO (0.02–0.19%), MnO (0.01–0.38%), TiO2 (0.01–0.10%), P2O5
(0.003–0.012%), Ba (3–162 ppm), and Sr (4.3–34.4 ppm). Hydrothermal zircons from the mineralized Wagone pluton show an anomalous lack of zoning and vermicular, spongy internal structures, and they contain high concentrations of Ti, Y, U, and light REEs but low Th/U ratios (mostly < 0.1). These features suggest slow
crystallization from a U-enriched and Th-depleted residual magmatic fluid under relatively cool and reducing
conditions. LA-ICPMS U–Pb dating of magmatic and hydrothermal zircons from the two granites yielded concordant ages of 61–60 Ma, indicating an Early Paleogene magmatic-mineralization event. Geochemical and geochronological data suggest that these A-type granites have a crustal origin and were produced by partial melting of a felsic clay-rich source in a back-arc extensional setting. The magmas may have ascended relatively slowly in the crust and experienced crystal fractionation and upper crustal contamination, contributing to intensive Sn–W mineralization in the Dawei area.

A B S T R A C T The Meishan iron deposit contains 338 Mt of iron-ore reserves at 39% Fe and represents the largest magneti-te–apatite deposit in the Ningwu Basin of eastern China. Controversy has long existed about whether this deposit had a hydrothermal or iron-oxide melt origin. Iron mineralization is genetically related to plutons that are composed of gabbro-diorite, which were emplaced at 130 ± 1 Ma. These rocks have SiO 2 contents of 51.72–54.60 wt%, Na 2 O contents of 3.47–4.04 wt%, K 2 O contents of 2.02–2.69 wt%, and K 2 O/Na 2 O ratios of 0.51–0.73. These rocks are enriched in LILEs and LREEs and depleted in Nb, Ta, and Ti, which indicates that the magma originated through partial melting of an enriched lithospheric mantle source in a subduction environment. A pattern of decreasing initial Sr isotopic ratios and increasing εNd(t) values with time in Early Cretaceous magmatic rocks of the Ningwu Basin may indicate incorporation of increasing proportions of asthenospheric mantle material into the source magma, which is consistent with the processes of lithospheric thinning and asthenospheric upwelling in eastern China related to Mesozoic subduction of the Paleo-Pacific Plate. Two stages of magnetite are found in the gabbro-diorite: (1) early-crystallized magnetite as euhedral–subhedral crystals in larger clinopyroxene crystals, and (2) later-crystallized magnetite and accompanying ilmenite grains in the voids between plagioclase and clinopyroxene crystals. The formation of magnetite before clinopyroxene, combined with the results of Fe–Ti oxide geothermometry and analysis of magnetite V content, indicates that the oxygen fugacity of the source magma was greater than ΔFMQ +2.2 at an early stage (> 640 °C) but decreased to ΔFMQ −2.66 as abundant magnetite crystallized at a later stage (∼489 °C). The early crystallization of magnetite at a high oxygen fugacity does not support a Fenner evolution trend for the primitive magma and diminishes the likelihood of liquid immiscibility, which could have generated an iron-rich melt, and is thus inconsistent with an iron-oxide melt origin for the Meishan iron deposit. The δ 34 S values of pyrite (6.6–15.1‰) and anhydrite (15.6–16.9‰) in the deposit and the occurrence of evaporites under the volcanic rocks likely indicate that the iron ores and alteration rocks of the Meishan deposit were formed by the circulation of fluids of evaporitic origin driven by heat from the hypabyssal gabbro-diorite intrusives. In the late magmatic stage, oxygen fugacity decreased to a reducing range, triggering the reduction of sulfate to reduced sulfur and leading to local gold and pyrite mineralization.

Websterite and garnet orthopyroxenite and clinopyroxenite dykes crosscutting harzburgite occur in the hanging wall of a Cretaceous eclogitized continental fragment of the Upper Austroalpine Unit in the Eastern Alps. The dyke textures reflect pressure-temperature changes from the mantle, subduction channel and an accretionary wedge. A clinopyroxenite dyke, dated at 252 ± 2 Ma on zircon by U\ \Pb SIMS, provided ε Hf (t) zircon values of 16-8 (av. 11 from 18 spots) suggesting a depleted mantle source. The rock modal mineral composition and the mineral and whole-rock chemistry revealed that the pyroxenite dykes' petrogenesis is most likely related to sub-crustal cumulate-type melt derivates, less evolved for websterites and highly evolved for clino-and orthopyroxenites. The porphyroclastic clinopyroxene1 (10-13 mol% CaTs), orthopyroxene1, spinel1 and amphibole1 are inferred remnants after magmatic phases. They contain Ti-spinel and ilmenite exsolutions which indicate cooling of the dykes in harzburgite in a Spl stability field (D0-1 stage). Garnet exsolutions in Cpx1, Opx1 and Amp1, and Cpx exsolutions in Amp1 document continuous cooling and/or pressure increase (D0-2 stage). The Grt coronas around Spl1, Opx1, Cpx1 and Amp1, and the granoblastic matrix of Prp-Grs-rich Grt (or Cr-Spl in websterites), low-Al Cpx, low-Al Opx, Fe-enriched olivine, zoisite, kyanite, rutile and pargasite record a subduction channel compression (D1 stage). While the formation of Cpx-Grt or Amp-Grt symplectites replacing the Cpx1 and Amp1 rims suggests the HP-HT decompression (D2-1 exhumation stage). The Grt (or Cr-Spl) replacement by Spl, and Opx1, Cpx1 and Prg replacement by Ol-Spl, Opx-Spl or Prg-Spl symplectites document continuous HT decompression (D2-2 exhumation stage). The MP/MT-LT conditions were estimated from tremolite, Grs-rich Grt, Sr-epidote, clinozoisite, Cl-apatite, titanite, Ce-allanite, chlorite, serpentine and talc assemblage (D3 stage). Anticlockwise P-T path was reconstructed for the D0 to D1 stages followed by almost isothermal exhumation (D2) and emplacement in the Cretaceous accretionary wedge (D3). The pseudosection P-T calculation from a clinopyroxenite dyke yielded 850-825 °C and 25-28 kbar (D1). The whole-rock and mineral trace element data of relic Cpx1 and Amp1, Grt(1-3), Ep-Zo, and younger zircon ages due to Pb-loss, reflect the impact of metamorphic fluids during the D1 to D3 evolutionary stages.

Petrologic monitoring of Kīlauea Volcano from January 1983 to October 2013 has yielded an extensive record of glass, phenocryst, melt inclusion, and bulk‐lava chemistry from well‐quenched lava. When correlated with 30+ years of geophysical and geologic monitoring, petrologic details testify to physical maturation of summit‐ to‐rift magma plumbing associated with sporadic intrusion and prolonged magmatic overpressurization. Changes through time in bulk‐lava major‐ and trace‐element compositions, along with glass thermometry, record shifts in the dynamic balance of fractionation, mixing, and assimilation processes inherent to magma storage and transport during near‐continuous recharge and eruption. Phenocryst composition, morphology, and texture, along with the sulfur content of melt inclusions, constrain coupled changes in eruption behavior and geochemistry to processes occurring in the shallow magmatic system. For the first 17 years of eruption, magma was steadily tapped from a summit reservoir at 1–4 km depth and circulating between 1180 and 1200°C. Furthermore, magma cooled another 30°C while flowing through the 18 km long rift conduit, before erupting olivine‐spinel‐phyric lava at temperatures of 1150–1170°C in a pattern linked with edifice deformation, vent formation, eruptive vigor, and presumably the flux of magma into and out of the summit reservoir. During 2000–2001, a fundamental change in steady state eruption petrology to that of relatively low‐temperature, low‐MgO, olivine(‐spinel)‐clinopyroxene‐plagioclase‐phryic lava points to a physical transformation of the shallow volcano plumbing uprift of the vent. Preeruptive comagmatic mixing between hotter and cooler magma is documented by resorption, overgrowth, and compositional zonation in a mixed population of phenocrysts grown at higher and lower temperatures. Large variations of sulfur (50 to >1000 ppm) in melt inclusions within individual phenocrysts and among phenocrysts in most samples provide an unequivocal glimpse of rapid crystal growth amid sulfur degassing at <30 MPa in a turbulent preeruptive environment. We speculate that, during the last decade, one or more shallow open‐system reservoirs developed along the conduit between the summit and Pu'u 'Ō'ō and now serve to buffer the magmatic throughput associated with ongoing recharge and eruption. Lava with identical trace‐element signatures erupted simultaneously at the summit and at Pu'u 'Ō'ō from 2008 to 2013 confirms magmatic continuity between the vents. Complementary changes in compositions of matrix glasses, phenocrysts, and melt inclusions of summit tephra are mirrored by similar changes in contempo-raneous rift lava at eruption temperatures 20–35°C lower than those at the summit. Petrologic parameters measured at opposite ends of the shallow magmatic plumbing system are both correlated with summit deformation, demonstrating that effects of summit magma chamber pressurization are translated throughout interconnected magma pathways in the shallow edifice.

This paper presents crystal chemistry and U-Pb isotopic data for titanite (or sphene, CaTiSiO 5) from Precambrian granitoid plutons of distinct tectonic settings within the Eastern Brazilian shield. Despite the fact that most titanite ages are related to partial lead-loss, resetting or crystallization during metamorphic events, chemistry data reflect the magmatic history of the plutons, specially the Ti 4+ /Al+Fe 3+ ratio. It is demonstrated that for plutons of different crystallization ages (Archean, Paleoproterozoic and Neoproterozoic) the measured Ti 4+ /Al+Fe 3+ ratios of titanite grains are characteristic of the source region from which the magma was extracted, and the ratios remain unchanged during subsequent metamorphic events. Higher Ti 4+ /Al+Fe 3+ values (> 9) are found in predominantly mantle-derived granitoid plutons whilst crust-derived granitoid rocks have lower ratios. Therefore, titanite crystal chemistry may be used to discriminate magma sources of granitoid rocks regardless their age and metamorphic history.

Based on the REE and other trace elements abundances and Nd, Pb isotopic ratios we distinguish three phases on the development of the Triassic magmatism: 1. Lower Triassic volcanism in a continental rifting environment. Volcanic rocks are significantly enriched, compare to MORB, on LREE and other trace elements typical for the continental crust. The negative value of εNd (-1,9)and Pb isotopic ratios indicate an enriched mantle magma source, close to EMI geochemical reservoir. 2. Middle Triassic volcanic and plutonic rocks formed in the continental extension conditions. Volcanic rocks are less enriched, compare to low Triassic volcanic rocks, on LREE and other trace elements typical for the continental crust. The low values of εNd and Pb isotopic ratios indicate a less enriched mantle magma source, but clearly different from the MORB. Middle Triassic plutonic massifs, mainly granitoides, are of the type A, A2. 3. Middle Triassic – Lower Jurassic volcanic rocks of the volcanic-sedimentary series formed in the spreading conditions, probably in a BAB. These rocks have the geochemical signatures close to MORB , but some high values of the trace elements typical for the continental crust may indicate probably the BABB's. The εNd and Pb isotopic ratios values are close to MORB.

Inclusions of calcite within large euhedral apatite crystals from the pyroxenite-carbonatite-syenite complex of Sevattur, Tamil Nadu, south India, were identified to represent inclusions of a primary carbonatitic melt (calcite I) from which the apatites have crystallized. The apatites themselves are embedded into a younger batch of calcite-carbonatitic melt (calcite II). Using the synchrotron XRF microprobe at beamline L at HASYLAB/DESY (Hamburg), the concentrations of the trace elements Ba, Sr, Y, Zr, Th, La, Ce, Nd, Sm, Gd, Dy, and Er were determined both in melt inclusions as well as in host apatites and younger carbonatite matrix. Unexpected high REE concentrations were found not only in apatite but also in calcite, especially of the younger matrix phase, in agreement with the whole rock geochemistry. The data reveal an equilibrium distribution between melt inclusions and host apatite that allows the calculation of partition coefficients D = C i Ap / C i Cc=melt for elements of interest. Assuming 9% crystallization of the melt, which can be calculated from the whole rock analyses, the composition of the primary carbonatite melt prior to apatite crystallization can be determined. This composition is, with the exception of only few elements, nearly equal to that of the younger matrix carbonatite melt (calcite II), and thus gives evidence for the existence of different pulses of carbonatite melt during crystallization and consolidation of the carbonatite body. The results allow new insights into the processes of trace element and REE distribution between the two major igneous components of carbonatites and thus into the question of carbonatitic fractionation processes. The data reveal that mere apatite crystallization and fractionation does not lead to enriched REE compositions during carbonatite evolution but lowers their concentrations in the residual melts. But alternatively, if segregated apatite is collected and incorporated by a new melt batch, the overall REE of this melt will be increased.

Abstract The Meishan iron deposit contains 338 Mt of iron-ore reserves at 39% Fe and represents the largest magnetite–apatite deposit in the Ningwu Basin of eastern China. Controversy has long existed about whether this deposit had a hydrothermal or iron-oxide melt origin. Iron mineralization is genetically related to plutons that are composed of gabbro-diorite, which were emplaced at 130 ± 1 Ma. These rocks have SiO2 contents of 51.72–54.60 wt%, Na2O contents of 3.47–4.04 wt%, K2O contents of 2.02–2.69 wt%, and K2O/Na2O ratios of 0.51–0.73. These rocks are enriched in LILEs and LREEs and depleted in Nb, Ta, and Ti, which indicates that the magma originated through partial melting of an enriched lithospheric mantle source in a subduction environment. A pattern of decreasing initial Sr isotopic ratios and increasing eNd(t) values with time in Early Cretaceous magmatic rocks of the Ningwu Basin may indicate incorporation of increasing proportions of asthenospheric mantle material into the source magma, which is consistent with the processes of lithospheric thinning and asthenospheric upwelling in eastern China related to Mesozoic subduction of the Paleo-Pacific Plate. Two stages of magnetite are found in the gabbro-diorite: (1) early-crystallized magnetite as euhedral–subhedral crystals in larger clinopyroxene crystals, and (2) later-crystallized magnetite and accompanying ilmenite grains in the voids between plagioclase and clinopyroxene crystals. The formation of magnetite before clinopyroxene, combined with the results of Fe–Ti oxide geothermometry and analysis of magnetite V content, indicates that the oxygen fugacity of the source magma was greater than ΔFMQ +2.2 at an early stage (&gt;640 °C) but decreased to ΔFMQ −2.66 as abundant magnetite crystallized at a later stage (∼489 °C). The early crystallization of magnetite at a high oxygen fugacity does not support a Fenner evolution trend for the primitive magma and diminishes the likelihood of liquid immiscibility, which could have generated an iron-rich melt, and is thus inconsistent with an iron-oxide melt origin for the Meishan iron deposit. The δ34S values of pyrite (6.6–15.1‰) and anhydrite (15.6–16.9‰) in the deposit and the occurrence of evaporites under the volcanic rocks likely indicate that the iron ores and alteration rocks of the Meishan deposit were formed by the circulation of fluids of evaporitic origin driven by heat from the hypabyssal gabbro-diorite intrusives. In the late magmatic stage, oxygen fugacity decreased to a reducing range, triggering the reduction of sulfate to reduced sulfur and leading to local gold and pyrite mineralization.

Abstract Tin-tungsten-associated granites occur widely in the Dawei region of the Southeast Asian tin belt. In this contribution, we present a detailed study of zircon U–Pb geochronology and whole-rock and zircon elemental geochemistry for the Wagone and Hermyingyi granites in southern Myanmar, with the aim of determining their petrogenesis, mineralization associations, and tectonic setting. These granitic rocks, which belong to the high-K calc-alkaline series A 2 -type granites, are characterized by high concentrations of SiO 2 (75.2–82.5%), Rb (264–927 ppm), Th (18.4–58.3 ppm), U (10.4–18.3 ppm), and Y (33.5–212 ppm), but low contents of TFeO (0.57–3.45%), CaO (0.23–0.86%), MgO (0.02–0.19%), MnO (0.01–0.38%), TiO 2 (0.01–0.10%), P 2 O 5 (0.003–0.012%), Ba (3–162 ppm), and Sr (4.3–34.4 ppm). Hydrothermal zircons from the mineralized Wagone pluton show an anomalous lack of zoning and vermicular, spongy internal structures, and they contain high concentrations of Ti, Y, U, and light REEs but low Th/U ratios (mostly