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1.
Pinto Viter Magalhães Massonne Hans-Joachim Wildner Wilson Hartmann Léo Afraneo Debruyne David Theye Thomas 《Mineralogy and Petrology》2019,113(6):765-782
Mineralogy and Petrology - Mafic-ultramafic intrusions within continental flood basalt terrains are frequently associated with Cu-Ni-PGE mineralization. This study aims to constrain the... 相似文献
2.
Olivier Vidal Thomas Theye Christian Chopin 《Contributions to Mineralogy and Petrology》1994,118(3):256-270
The reaction chloritoid (ctd)=almandine (alm)+diaspore+H2O (CAD) has been reversed using Fe3+-free synthetic chloritoid and almandine, under fO2 conditions of the solid oxygen buffer Fe/FeO (CADWI), and using partially oxidized synthetic minerals under fO2 conditions of the solid oxygen buffer Ni/NiO (CADNNO). Experiments have been conducted between 550 and 700°C, 25 and 45 kbar. The equilibrium pressure and temperature conditions are strongly dependent on the fO2 conditions (CADNNO lies some-what 50°C higher than CADWI). This can be explained by a decrease in aH2O for experiments conducted on the Fe/FeO buffer, and a decrease in actd and aalm (through incorporation of ferric iron preferentially in chloritoid) for experiments conducted on the Ni/NiO buffer. The H2O activity has been calculated using the MRK equation of state, and the values obtained checked against the shift of the equilibrium diaspore=corundum+H2O bracketed on the Fe/FeO buffer and under unbuffered fO2 conditions. For fO2 buffered by the assemblage Fe/FeO, aH2O increases with pressure from about 0.85 at 600°C, 12 kbar to about 0.9 at 605°C, 25 kbar and 1 above 28 kbar. For fO2 buffered by the assemblage Ni/NiO, aH2O=1. The aH2O decrease from Ni/NiO to Fe/FeO is, however, too small to be entirely responsible for the temperature shift between CADNNO and CADWI. In consequence, the amount of ferric iron in almandine and chloritoid growing in the CADNNO experiments must be significant and change along the CADNNO, precluding calculation of the thermodynamic properties of chloritoid from this reaction. Our experimental data obtained on the Fe/FeO buffer are combined, using a thermodynamic analysis, with Ganguly's (1969) reversal of the reaction chloritoid=almandine+corundum +H2O (CAC) on the same oxygen buffer. Experimental brackets are mutually consistent and allow extraction of the thermodynamic parameters H
o
f,ctd and S
octd. Our thermodynamic data are compared with others, generally calculated using Ganguly's bracketing of CACNNO. The agreement between the different data sets is relatively good at low pressure, but becomes rapidly very poor toward high pressure conditions. Using our thermodynamic data for chloritoid and KD=(Fe3+/Al)ctd/(Fe3+/Al)alm estimated from natural assemblages, we have calculated the composition of chloritoid and almandine growing from CADNNO and CACNNO. The Fe3+ content in chloritoid and almandine increases with pressure, from less than 0.038 per FeAl2SiO5(OH)2 formula unit at 10 kbar to at least 0.2 per formula unit above 30 kbar. This implies that chloritoid and almandine do contain Fe3+ in most natural assemblages. The reliability of our results compared to natural systems and thermodynamic data for Mg-chloritoid is tested by comparing the equilibrium conditions for the reaction chloritoid+quartz=garnet (gt)+kyanite+H2O (CQGK), calculated for intermediate Fe–Mg chloritoid and garnet compositions, from the system FASH and from the system MASH. For 0.65<(XFe)gt<0.8, CQKG calculated from FASH and MASH overlap for KD=(Mg/Fe)ctd/(Mg/Fe)gt=2. This is in good agreement with the KD values reported from chloritoid+garnet+quartz+kyanite natural assemblages. 相似文献
3.
In the low-grade, high-pressure (400°C, 10 kbar) metamorphic Phyllite-Quartzite Unit of Western Crete, widespread occurrences of aragonite marbles have been discovered recently. A sedimentary precursor is proved by relic structures (bedding, fossils). Partial or complete transformation of aragonite into calcite is ubiquitous. Compositional and microstructural features reflect the metamorphic history: (1) The high-pressure stage is documented by aragonite that is chemically characterized by incorporation of variable amounts of Sr and the lack of Mg. The most Sr-rich aragonite has about 9 wt% SrO (X
Sr
arag
=0.09). A compositional zoning observed in some aragonite crystals may be due to the prograde divariant calcitearagonite transformation in the system CaCO3-SrCO3. Because the parent rocks probably were Sr-poor calcite limestones, one can speculate that strontium has been supplied from an external source under high-pressure conditions. (2) During uplift, calcite replacing aragonite did not equilibrate with unreplaced aragonite. Disequilibrium is indicated by highly variable compositions of calcite crystals that show topotactic relations to the host aragonite. The calcite compositions range from that of the host aragonite (Sr-rich and Mg-free) to Mg-bearing and Sr-poor. (3) Calcite that recrystallized during retrogression is generally Sr-poor (mean value ofX
Sr<0.005), Mg-bearing (X
Mg0.010), and chemically homogeneous. Because practically no Sr remains in the calcite, an interaction with a fluid phase is indicated. In fine-grained calcite marbles rich in solid organic matter, microstructural features indicative of former aragonite may be present. (4) The last stage of retrogression is documented by the appearance of radiating aragonite in veins and nodules. This aragonite, which shows neither deformation nor retrogression, was probably formed metastably in a near-surface environment. 相似文献
4.
Eclogites from the Chinese continental scientific drilling borehole, their petrology and different P-T evolutions 总被引：1，自引：0，他引：1
Abstract Four phengite‐bearing eclogites, taken from different depths of the Chinese continental scientific drilling (CCSD) borehole in the Sulu ultrahigh pressure terrane, eastern China, were studied with the electron microprobe. The compositional zonations of garnet and omphacite are moderate, whereas phengite compositions generally vary significantly in a single sample from core to rim by decrease of the Si content. Various geothermobarometric methods were applied to constrain the P‐T conditions of these eclogites on the basis of the compositional variability of the above minerals. The constrained P‐T path for sample B218 is characterized by pressure decrease from ca 3.0 GPa (ca 600°C) to 1.3 GPa (ca 550°C). Eclogite B310 yielded P‐T conditions of 3.0 GPa and 750°C. The path for eclogite B1008 starts at about 650°C and 3.6–3.9 GPa (stage I) followed by a pressure decrease to 2.8–3.0 GPa and a significant temperature rise (stages II and IIIa, 750–810°C). Afterwards, this rock cooled down to 620–660°C at still high pressures (2.5–2.7 GPa, stage IIIb). Retrograde conditions were about 670°C and 1.3 GPa (stage IV). Eclogite B1039 yielded a P‐T path starting at ca 600°C and 3.3–3.9 GPa (stage I). A pressure decrease to about 3.0 GPa (stage II, 590–610°C) and then a moderate isobaric temperature increase to ca 630°C (stage III) followed. Stage IV is characterized by temperatures of 650°C at pressures close to 1.3 GPa. During and after this stage (hydrous) fluids partially rich in potassium penetrated the rocks causing minor changes. Relatively high oxygen fugacities led to andradite and magnetite among the newly formed minerals. We think that the above findings can be best explained by mass flow in a subduction channel. Thus, we conclude that the assembly of UHP rocks of the CCSD site, eclogites, quartzofeldspathic rocks, and peridotites, cannot represent a crustal section that was already coherent at UHP conditions as it is the common belief currently. The coherency was attained after significant exhumation of these UHP rocks. 相似文献
5.
Manfred R. Brix Bernhard Stckhert Eberhard Seidel Thomas Theye Stuart N. Thomson Martina Küster 《Tectonophysics》2002,349(1-4)
A fossil partial annealing zone of fission tracks in zircon is described from high pressure–low temperature (HP–LT) rocks of the Phyllite–Quartzite Unit (PQ) on the island of Crete, Greece. Correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data, and with new experimental annealing results, allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples.The zircon fission track (FT) ages of samples from the PQ across Crete range from original detrital signature through reduced to completely reset. The annealing is the result of a single heating period related to the HP–LT metamorphism with near-peak temperatures lasting for only a few million years some time between 24±1 and 20±1 Ma. In eastern Crete, where rocks have experienced temperatures of 300±50 °C and pressures of 0.8±0.3 GPa, zircon FT ages range from 414±24 to 145±10 Ma. Ages above 300 Ma occur mostly near the east coast of the island in rocks which have not been heated to above ca. 280 °C and probably represent a pre-Variscan source. Track lengths are already indicative of a substantial annealing at this temperature. Most of the zircon FT ages from eastern Crete scatter within error around the stratigraphic age. Samples with apparent zircon FT ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca. 320 °C. Towards the west, a sudden decrease to very young ages ranging from 17±2 to 18±1 Ma reflects a complete resetting at ca. 350 °C. Short tracks, however, are still observed. Throughout the central and western part of the island, ages are consistently below 22 Ma. Thermobarometric data for this area indicate maximum temperatures of 400±50 °C and pressures of 1±0.3 GPa. Only samples from western Crete, which have been exposed to 400±50 °C, show exclusively long tracks. Consequently, the high temperature limit of the zircon partial annealing zone (ZPAZ) appears to be between 350 and 400 °C.A significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0.5 GPa and at different temperatures, which fit the curves previously obtained by other authors at ambient pressure. 相似文献
6.
Detrital blue amphibole was found for the first time in two samples of the Famennian section of the South Harz-Selke Graywacke and the Tanne Graywacke (Middle Visean) of the Harz Mountains. Microprobe analyses reveal that the blue amphiboles represent glaucophane with Fe3+/(Fe3++AlVI)=0.22 molar ratio. The minimum pressure required for the formation of glaucophane of this composition is estimated to be approximately 8 kbar. The source area of the detrital glaucophane is assumed to be located between the Northern Phyllite Zone and the Mid-German Crystalline Rise, in areas which have been downfaulted (?subducted) during the Variscan orogeny. The age of blueschist-facies metamorphism in the source area must be of pre-Upper Devonian age. This metamorphic event is significantly older than the Lower Carboniferous high-pressure/low-temperature metamorphism documented in parts of the northern Phyllite zone. Hence, the convergent tectonics connected with blueschist-facies metamorphism is not restricted to the Lower Carboniferous, but can be traced back at least to the early Upper Devonian. These data are in accordance with a southerly directed underplating (?subduction) at the northern margin of the Saxothuringian zone active during at least from early Upper Devonian to Lower Carboniferous. 相似文献
7.
Evidence for oceanic subduction at the NE Gondwana margin during Permo-Triassic times 总被引：4，自引：0，他引：4
Blueschist was recently recognized within the Lhasa terrane, which is one of the NE Gondwana blocks. In this rock, the Mn and Mg contents of garnet enclosing aegirine-rich clinopyroxene, rutile and quartz decrease and increase, respectively, from core to rim. Amphibole changes from glaucophane through Na–Ca amphibole to Ca amphibole. The Si contents of phengite are high in the centre but low along the rim. The P – T path, starting above 2.5 GPa–450 °C and showing subsequently first a temperature increase to 500 °C and then a pressure release via blueschist conditions to 0.6 GPa, was reconstructed using a P – T pseudosection calculated for the P – T range 0.4–2.8 GPa and 250–650 °C. This path points to deep subduction of a cold oceanic crust probably beneath the NE Gondwana margin during Permo-Triassic times. This finding contributes to a better understanding of the pre-Cenozoic history of major terranes of NE Gondwana. 相似文献
8.
Within the Namche Barwa area, SE Tibet, the Indus–Yarlung suture zone separates the Lhasa terrain in the north from the Himalayan unit including the Tethyan (sedimentary and volcanic rocks), Dongjiu (greenschist to lower amphibolite facies), Namche Barwa (granulite facies), Pei (amphibolite facies) and Laiguo (greenschist facies) sequences in the south. Two fault systems were distinguished in the Namche Barwa area. The former includes a top-down-to-the-north normal fault in the north and two top-to-the-south thrust zones in the south named as Upper and Lower Thrusts, respectively. The Namche Barwa and Pei sequences were exhumed southwards from beneath the Dongjiu sequence by these faults. Thus, the fault system is regarded as a southward extrusion structure. Subsequently, the exposed Dongjiu, Namche Barwa, Pei and Laiguo sequences were displaced northwards onto the Lhasa terrain by the top-to-the-north fault system, thus, marking it as northward indentation structure. Monazite TIMS U–Pb dating demonstrates that the normal fault and the Lower Thrust from the southward extrusion system were probably active at ~ 6 Ma and ~ 10 Ma, respectively. Zircon U–Pb SHRIMP and phlogopite K–Ar ages further suggest that the Upper Thrust was active between 6.2 ± 0.2 Ma and 5.5 ± 0.2 Ma. The northward indentation structures within the core portion of the eastern Himalayan syntaxis were perhaps active between 3.0 Ma and 1.5 Ma, as inferred by published zircon U–Pb SHRIMP and hornblende Ar–Ar ages. The monazite from upper portions of the Pei sequence dated by U–Pb TIMS indicates that the precursor sediments of this sequence were derived from Proterozoic source regions. Nd isotopic data further suggest that all the metamorphic rocks within eastern Himalaya (εNd = ? 13 to ? 19) correlate closely with those from the Greater Himalayan Sequences, whereas the western Himalayan syntaxis is mainly comprised of Lesser Himalayan Sequences. The two indented corners of the Himalaya are, thus, different. 相似文献
9.
Petrogenesis of early cretaceous carbonatite and ultramafic lamprophyres in a diatreme in the Batain Nappes,Eastern Oman continental margin 总被引：1，自引：0，他引：1
S. Nasir S. Al-Khirbash H. Rollinson A. Al-Harthy A. Al-Sayigh A. Al-Lazki T. Theye H.-J. Massonne E. Belousova 《Contributions to Mineralogy and Petrology》2011,161(1):47-74
Allochthonous carbonatite and ultramafic lamprophyre occur in a diatreme at the beach of the Asseelah village, northeastern
Oman. The diatreme consists of heterogeneous deposits dominated by ‘diatreme facies’ pyroclastic rocks. These include aillikite
and carbonatite, which intrude late Jurassic to early Cretaceous cherts and shales of the Wahra Formation within the Batain
nappes. Both rock types are dominated by carbonate, altered olivine, Ti–Al–phlogopite and Cr–Al–spinel and contain varying
amounts of apatite and rutile. The carbonatite occur as fine-grained heterolithic breccias with abundant rounded carbonatite
xenoliths, glimmerite and crustal xenoliths. The aillikite consists of pelletal lapilli tuff with abundant fine-grained carbonatite
autoliths and crustal xenoliths, which resemble those in the carbonatite breccia. The aillikite and carbonatite are characterized
by low SiO2 (11–24 wt%), MgO (9.5–12.4 wt%) and K2O (<0.3 wt%), but high CaO (18–22 wt%), Al2O3 (4.75–7.04 wt%), Fe2O3tot (8.7–13.8 wt%) and loss-on-ignition (24–30 wt%). Higher CaO, Fe2O3total, Al2O3, MnO, TiO2, P2O5 and lower SiO2 and MgO content distinguish carbonatite from the aillikite. The associated carbonatite xenoliths and autoliths have intermediate
composition between the aillikite and carbonatite. Mg number is variable and ranges between 58 and 66 in the carbonatite,
66 and 72 in the aillikite and between 48 to 64 in the carbonatite autoliths and xenoliths. The Asseelah aillikite, carbonatite,
carbonatite xenoliths and autoliths overlap in most of their mineral parageneses, mineral composition and major and trace
element chemistry and have variable but overlapping Sr, Nd and Pb isotopic composition, implying that these rocks are related
to a common type of parental magma with variable isotopic characteristics. The Asseelah aillikite, carbonatite and carbonatites
xenoliths are LREE-enriched and significantly depleted in HREE. They exhibit similar smooth, subparallel REE pattern and steep
slopes with (La/Sm)
n
of 6–10 and relative depletion in heavy rare earth elements (Lu = 3–10 chondrite). Initial 87Sr/86Sr ratios vary from 0.70409 to 0.70787, whereas initial 143Nd/144Nd ratios vary between 0.512603 and 0.512716 (εNd
i
between 2.8 and 3.6). 206Pb/204Pb
i
ratios vary between 18.4 and 18.76, 207Pb/204Pb
i
ratios vary between 15.34 and 15.63, whereas 208Pb/204Pb
i
varies between 38.42 and 39.05. Zircons grains extracted from the carbonatite have a mean age of 137 ± 1 Ma (95% confidence,
MSWD = 0.49). This age correlates with large-scale tectonic events recorded in the early Indian Ocean at 140–160 Ma. Geochemical
and isotopic signatures displayed by the Asseelah rocks can be accounted for by vein-plus-wall-rock model of Foley (1992) wherein veins are represented by phlogopite, carbonate and apatite and depleted peridotite constitutes the wall-rock. The
carbonatite and aillikite magmatism is probably a distal effect of the breaking up of Gondwana, during and/or after the rift-to-drift
transition that led to the opening of the Indian Ocean. 相似文献
10.
Federico Rossetti Mohsen Nasrabady Gianluca Vignaroli Thomas Theye Axel Gerdes Mohammad Hossein Razavi Hosein Moin Vaziri 《地学学报》2010,22(1):26-34
The ophiolitic mélange of the Sabzevar Range (northern Iran) is a remnant of the Mesozoic oceanic basins on the northern margin of the Neotethys that were consumed during the Arabia–Eurasia convergence history. Occurrence of km-scale, dismembered mafic HP granulitic slices is reported in this study. Granulites record an episode of amphibole-dehydratation melting and felsic (tonalite/throndhjemite) melt segregation at c. 1.1 GPa and 800 °C. In situ U(-Th)–Pb geochronology of zircon and titanite grains hosted in melt segregations points to an Early Cretaceous (Albian) age for the metamorphic climax. Results of this study (i) impose reconsideration of the current palaeotectonic models of the Neothetyan convergent margin during the Early Cretaceous and (ii) argue that punctuated events of subduction of short-lived back-arc oceanic basins accompanied the long-lasting history of the Neotethyan subduction in the region. 相似文献