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991.
Phase relations of phlogopite with magnesite from 4 to 8 GPa 总被引:2,自引:2,他引:0
Andreas?EnggistEmail author Linglin?Chu Robert?W.?Luth 《Contributions to Mineralogy and Petrology》2012,163(3):467-481
To evaluate the stability of phlogopite in the presence of carbonate in the Earth’s mantle, we conducted a series of experiments
in the KMAS–H2O–CO2 system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl90-mag10; wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550°C. We bracketed the solidus between
1,200 and 1,250°C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200°C at a pressure of 7 GPa. Below the solidus,
phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite
and olivine appear. Phlogopite melts over a temperature range of ~150°C. The amount of garnet increases above solidus from
~10 to ~30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed
with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures ≥5 GPa. Relative to CO2-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a
subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of ~7.5 GPa. In a
cold (40 mWm−2) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist
with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths
could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate
at a depth of 180–200 km. 相似文献
992.
Nicole?E.?MooreEmail author Susan?M.?DeBari 《Contributions to Mineralogy and Petrology》2012,163(3):521-546
Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive
dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and
have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that
crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three
primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical
calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt
of Park Butte (49.3–50.3 wt% SiO2, Mg# 64–65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest
overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted
mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of
Lake Shannon (50.7–52.6 wt% SiO2, Mg# 58–62) and Sulphur Creek (51.2–54.6 wt% SiO2, Mg# 56–57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element
patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or
fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8–54.0 wt% SiO2, Mg# 68–70) and the HMA of Glacier Creek (58.3–58.7 wt% SiO2, Mg# 63–64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO2 suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite
unit, Cathedral Crag (52.2–52.6 wt% SiO2, Mg# 55–58), is an Mg-poor differentiate of the Type 3 endmember. The calc-alkaline lavas are least enriched in a subduction
component (lowest H2O, Sr/PN, and Ba/Nb), the LKOT-like lavas are intermediate (moderate Sr/PN and Ba/Nb), and the HMBA are most enriched (highest H2O, Sr/PN and Ba/Nb). The generation of the LKOT-like and calc-alkaline lavas can be successfully modeled by partial melting of a spinel
lherzolite with variability in composition of slab flux and/or mantle source depletion. The HMBA lavas can be successfully
modeled by partial melting of a garnet lherzolite with slab flux compositionally similar to the other lava types, or less
likely by partial melting of a spinel lherzolite with a distinctly different, HREE-depleted slab flux. 相似文献
993.
Matthieu?E.?GalvezEmail author Olivier?Beyssac Karim?Benzerara Nicolas?Menguy Sylvain?Bernard Simon?C.?Cox 《Contributions to Mineralogy and Petrology》2012,164(5):895-914
Understanding the mobility of chemical elements during fluid–rock interactions is critical to assess the geochemical evolution of a rock undergoing burial and metamorphism and, more generally, to constrain the geochemical budget of the subduction factory. In particular, determining the behavior and mobility of Ti in aqueous fluids constitutes a great challenge that is still under scrutiny. Here, we study plant fossils preserved in blueschist metasedimentary rocks from the Marybank Formation (New Zealand). Using scanning and transmission electron microscopies (SEM and TEM), we show that the carbonaceous material (CM) composing the fossils contains abundant nano-inclusions of Ti- and Fe-oxides. These nanocrystals are mainly anatase, rutile, and Fe–Ti oxides. The mineral composition observed within the fossils is significantly different from that detected in the surrounding rock matrix. We propose that Ti and Fe might have been mobilized by the alteration of a detrital Ti–Fe-rich protolith during an early diagenetic event under acidic and reducing conditions. Aqueous fluids rich in organic ligands released by the degradation of organic matter may have been involved. Moreover, using mass balance and petrological observations, we show that the contrasted mineralogy between the rock matrix and the fossil CM might be the consequence of the chemical isolation of fossil CM during the prograde path of the rock. Such an isolation results from the early formation of quartz and Fe-rich phyllosilicate layers enclosing the fossil as characterized by SEM and TEM investigations. Overall, this study shows that investigating minerals associated with CM down to the nanometer scale in metamorphic rocks can provide a precious record of early prograde geochemical conditions. 相似文献
994.
Maciej J. Bojanowski Bogus?aw Bagiński Euan Clarkson Ray Macdonald Leszek Marynowski 《Contributions to Mineralogy and Petrology》2012,164(2):245-259
Zircon occurs in voids and cracks in phosphatic coprolites enclosed in siderite concretions in Mississippian shales near Edinburgh, Scotland. The zircon formed during hydrothermal alteration of early-diagenetic concretions and occurs as spherical aggregates of prismatic crystals, sometimes radiating. Vitrinite reflectance measurements indicate temperatures of ~270°C for the zircon-bearing concretions and the host shales. Molecular parameter values based on dibenzothiophene and phenanthrene distribution and occurrence of di- and tetra-hydro-products of polycyclic aromatic compounds suggest that the rocks experienced relatively high-temperature aqueous conditions related to hydrothermal fluids, perhaps associated with neighboring mafic intrusions. The zircon was dissolved from the concretions, transported in fluids, and reprecipitated in voids. This is the first record of the precipitation of authigenic zircon in sedimentary rock as a new phase, not as outgrowths. 相似文献
995.
Karl?Hans?Wedepohl Klaus?SimonEmail author 《Contributions to Mineralogy and Petrology》2012,164(4):693-696
During the Variscan orogeny in Central Europe, partial melting in the lower continental crust formed granitic magmas, which intruded into the upper crust and left compounds of Ca (plus Eu2+), Mg, etc. in the lower crust. From the late Paleozoic decomposition of the tonalitic upper crust, sedimentary graywackes were produced reflecting the composition of this crust. The repeated reworking of the sedimentary cover caused the formation of sands. Sandstones as their products of consolidation contain increasing fractions of quartz and decreasing feldspar from Carboniferous and Triassic to Cretaceous age. A distinct negative Eu anomaly characterizes the majority of these rocks. The latter is imprinted by the Variscan magmatism. Quartz as used for numerous Medieval wood ash glasses is marked for its Central European origin by a distinct negative Eu anomaly in contrast to many soda glasses produced outside Germany mostly with a small or none Eu anomaly. 相似文献
996.
During the last two decades, there has been growing interest in the integration of existing ideas and data to produce new
synthetic models and hypotheses leading to discovery and advancement in estuarine and coastal science. This essay offers an
integrated definition of what is meant by synthesis research and discusses its importance for exploiting the rapid expansion
of information availability and for addressing increasingly complex environmental problems. Approaches and methods that have
been used in published synthetic coastal research are explored and a list of essential steps is developed to provide a foundation
for conducting synthetic research. Five categories of methods used widely in coastal synthesis studies are identified: (1)
comparative cross-system analysis, (2) analysis of time series data, (3) balance of cross-boundary fluxes, (4) system-specific
simulation modeling, and (5) general systems simulation modeling. In addition, diverse examples are used to illustrate how
these methods have been applied in previous studies. We discuss the urgent need for developing curricula for classroom and
experiential teaching of synthesis in coastal science to undergraduate and graduate students, and we consider the societal
importance of synthetic research to support coastal resource management and policy development. Finally, we briefly discuss
the crucial challenges for future growth and development of synthetic approaches to estuarine and coastal research. 相似文献
997.
W. Siebel C. K. Shang E. Thern M. Dani?ík J. Rohrmüller 《International Journal of Earth Sciences》2012,101(8):2105-2123
Correct interpretation of zircon ages from high-grade metamorphic terrains poses a major challenge because of the differential response of the U–Pb system to metamorphism, and many aspects like pressure–temperature conditions, metamorphic mineral transformations and textural properties of the zircon crystals have to be explored. A large (c. 450?km2) coherent migmatite complex was recently discovered in the Bohemian Massif, Central European Variscides. Rocks from this complex are characterized by granulite- and amphibolite-facies mineral assemblages and, based on compositional and isotopic trends, are identified as the remnants of a magma body derived from mixing between tonalite and supracrustal rocks. Zircon crystals from the migmatites are exclusively large (200–400?μm) and yield 207Pb/206Pb evaporation ages between 342–328?Ma and single-grain zircon fractions analysed by U–Pb ID-TIMS method plot along the concordia curve between 342 and 325?Ma. High-resolution U–Pb SHRIMP analyses substantiate the existence of a resolvable age variability and yield older 206Pb/238U ages (342–330?Ma, weighted mean age?=?333.6?±?3.1?Ma) for inner zone domains without relict cores and younger 206Pb/238U ages (333–320?Ma, weighted mean age?=?326.0?±?2.8?Ma) for rim domains. Pre-metamorphic cores were identified only in one sample (206Pb/238U ages at 375.0?±?3.9, 420.3?±?4.4 and 426.2?±?4.4?Ma). Most zircon ages bracket the time span between granulite-facies metamorphism in the Bohemian Massif (~345?Ma) and the late-Variscan anatectic overprint (Bavarian phase, ~325?Ma). It is argued that pre-existing zircon was variously affected by these metamorphic events and that primary magmatic growth zones were replaced by secondary textures as a result of diffusion reaction processes and replacement of zircon by dissolution and recrystallization followed by new zircon rim growth. Collectively, the results show that the zircons equilibrated during high-grade metamorphism and record partial loss of radiogenic Pb during post-peak granulite events and new growth under subsequent anatectic conditions. 相似文献
998.
Bernard?HenryEmail author Kalin?Naydenov Dimo?Dimov Diana?Jordanova Neli?Jordanova 《International Journal of Earth Sciences》2012,101(3):747-759
The Kapitan-Dimitrievo pluton was emplaced within the 15 km wide Maritsa shear zone during the Late Cretaceous. It has well-known
U–Pb zircon age (78.54 ± 0.13 Ma) and appears as a late-syntectonic intrusion that marked the last ductile deformation in
the Maritsa shear zone. Magnetite is believed to be the main carrier of the magnetic fabric in this pluton, and crystallized
mainly late, after the main rock-forming minerals. Two fabrics are recorded, a visible syn-magmatic fabric (due to magma flow)
and magnetic late-magmatic fabric (related to regional stresses). Although different, both are mainly related to the shearing
along this shear zone. These results constrain in age the dextral strike-slip controlled emplacement and evolution of the
Late Cretaceous plutons from Central Bulgaria. 相似文献
999.
Jaroslava Hajná Ji?í ?ák Václav Kachlík Martin Chadima 《International Journal of Earth Sciences》2012,101(7):1855-1873
The Teplá–Barrandian unit (TBU) has long been considered as a simply bivergent supracrustal ‘median massif’ above the Saxothuringian subduction zone in the Variscan orogenic belt. This contribution reveals a much more complex style of the Variscan tectonometamorphic overprint and resulting architecture of the Neoproterozoic basement of the TBU. For the first time, we describe the crustal-scale NE–SW-trending dextral transpressional Krakovec shear zone (KSZ) that intersects the TBU and thrusts its higher grade northwestern portion severely reworked by Variscan deformation over a southeastern very low grade portion with well-preserved Cadomian structures and only brittle Variscan deformation. The age of movements along the KSZ is inferred as Late Devonian (~380–370?Ma). On the basis of structural, microstructural, and anisotropy of magnetic susceptibility data from the KSZ, we propose a new synthetic model for the deformation partitioning in the Teplá–Barrandian upper crust in response to the Late Devonian to early Carboniferous subduction and underthrusting of the Saxothuringan lithosphere. We conclude that the Saxothuringian/Teplá–Barrandian convergence was nearly frontal during ~380–346?Ma and was partitioned into pure shear dominated domains that accommodated orogen-perpendicular shortening alternating with orogen-parallel high-strain domains that accommodated dextral transpression or bilateral extrusion. The synconvergent shortening of the TBU was terminated by a rapid gravity-driven collapse of the thickened lithosphere at ~346–337?Ma followed by, or partly simultaneous with, dextral strike-slip along the Baltica margin-parallel zones, driven by the westward movement of Gondwana from approximately 345?Ma onwards. 相似文献
1000.
Paleo- and Neoproterozoic magmatic and tectonometamorphic evolution of the Isla Cristalina de Rivera (Nico Pérez Terrane, Uruguay) 总被引:1,自引:0,他引:1
Pedro Oyhant?abal Martin Wagner-Eimer Klaus Wemmer Bernhard Schulz Robert Frei Siegfried Siegesmund 《International Journal of Earth Sciences》2012,101(7):1745-1762
The Isla Cristalina de Rivera crystalline complex in northeastern Uruguay underwent a multistage magmatic and metamorphic evolution. Based on SHRIMP U–Pb zircon, Th–U–Pb monazite (CHIME-EPMA method) and K–Ar age data from key units several events can be recognized: (1) multistage magmatism at 2,171–2,114?Ma, recorded on zircon of the granulitic orthogneisses and their 2,093–2,077?Ma overgrowths; (2) a distinct amphibolite facies metamorphism at ~1,980?Ma, recorded by monazite; (3) greenschist facies reworking and shearing at ca. 606?Ma (monazite and K–Ar on muscovite) along the Rivera Shear Zone, and finally (4) intrusion of the post-tectonic Sobresaliente and Las Flores granites at around 585?Ma. Lithological similarities, geographic proximity and coeval magmatic and metamorphic events indicate a similar tectonometamorphic evolution for the Isla Cristalina de Rivera, the Valentines Block in Uruguay and the Santa María Chico Granulitic Complex in southern Brazil, since at least 2.1?Ga. 相似文献