Field and geochemical studies overviewed here reveal that the precursors of ultrahigh-temperature (UHT) metamorphic rocks of the Napier Complex in Enderby Land, East Antarctica, consist of mantle protolith (serpentinite and depleted peridotite), magmatic protolith (tonalite-trondhjemite-granodiorite (TTG) suite, basaltic to komatiitic rocks and anorthosite), and sedimentary protolith (MgO-, Ni-, Cr- and Co-rich sediments, impure quartzite, banded iron formation (BIF) and calc-silicate rock). This assemblage of protoliths, especially the komatiite-TTG association with minor anorthosite, is reminiscent of the Archaean greenstone-granite belts. The U-Pb SHRIMP or SIMS dating of zircons with oscillatory zoning and magmatic Th/U ratio from the TTG protoliths shows four age clusters such as ∼ 3.8, 3.3, 3.0 and 2.6 Gyr ago, suggesting the multi-stages of protolith formation. The modern analogy for the genesis of TTG suite suggests that the tectonic setting of the protolith formation and emplacement can be considered in the framework of the present-day intra-oceanic island-arc and related subduction regime. Subsequently, the Napier Complex was stabilized during the UHT metamorphism at ∼ 2.59-2.55 or ∼ 2.50-2.45 Gyr ago.
Recent geological and petrological investigations of the metamorphic rocks from Vietnam revealed the following new evidences to understand the tectonic evolution of Southeast Asia; 1) findings of ultrahigh-T (∼ 1000 °C) pelitic granulites, high- to ultrahigh-P (∼ 40 kbar) mafic metamorphic rocks and high-P/medium-T gneisses from the Kontum Massif, 2) eclogite and high-P granulite from the Song Ma suture zone, and 3) ultrahigh-T aluminous granulite from the Red River zone. These lines of evidence are strongly indicative of the highest- metamorphic conditions in each metamorphic terrane. Estimated P-T conditions and reaction textures from these rocks delineate a characteristic clockwise pressure-temperature-time (P-T-t) path for each other.. Based on the combination of P-T paths from these complexes, two-stages of metamorphic field gradient are identified. An earlier M0-stage of high-P/T gradient is recognized, based on the peak-P conditions from the Kontum Massif and Song Ma suture zone. A later M1-stage of low-P/T gradient is also identified by linking the peak metamorphic conditions from the Kontum Massif, the Song Ma suture zone and the Red River zone. The former metamorphic field gradient could represent an early continental collision event and the latter would indicate a peak metamorphic stage caused by very high-T magmatic intrusion (asthenosphere upwelling) as a heat source of ultrahigh-T metamorphism. A simultaneous collision metamorphism throughout Vietnam should have taken place during the continental collision between Indochina and South China cratons, which led to the formation of Trans Vietnam Orogenic Belt.
Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemically. Based on petrography, geochemistry and mineral compositions, metamorphic history and a reasonable tectonic model are proposed. Eclogites exposed in the Kaghan valley are classified into two groups. Group I eclogites appear as massive and Group II are lens-type. Group I eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, quartz, symplectite with rare epidote and phengite. Accessory minerals include abundant zircon, rutile, ilmenite, and rare apatite. Group II eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, phengite, quartz/coesite, epidote, and symplectite. In accessory minerals rutile and ilmenite are common while zircon and apatite are rare. Different types of protolith are proposed for these eclogites. Group I eclogites have higher FeO and TiO2 contents and trace element contents, and seem to be derived from gabbroic protolith. Group II eclogites have lower FeO and TiO2 and trace element contents and were derived from basalts. Pressure-temperature-time path was constructed for the Kaghan valley eclogites using various mineral assemblages along with textural relationship and inclusions study. At least three distinct metamorphic stages were identified. The first stage is the prograde garnet growth stage deduced from the inclusion paragenesis in garnet core. The second stage records the ultrahigh-pressure metamorphic stage deduced from the presence of coesite inclusions in omphacitic clinopyroxene. The third stage is the decompression stage and is deduced from the quartz-albite-amphibole symplectite portions. These petrological and geochemical results combined with isotopic ages reported elsewhere indicate that basalts and associated gabbroic dikes were emplaced at about 267 Ma when the Indian plate was moving northward and passing above an unknown hot spot. The closure of the Tethys and initiation of collision of the Indian plate with the Kohistan-Ladakh Island Arc is reported from 65-50 Ma. After that the leading-edge of the Indian plate underwent eclogite facies metamorphism at 49 Ma and when it reached to depths of about 100 km, the ultrahigh-pressure metamorphic event took place at 46 Ma.
This report concerns the Fe3+ solubility in cristobalite coexisting with hematite obtained from heating experiments in air at 990-1460 °C in the SiO2-Fe2O3 system. The ferric iron substitutes for the tetrahedral silicon in cristobalite and Si4+ also substitutes for the octahedral Fe3+ in hematite. Combining the chemical and P-T data of the quartz in the high-pressure eclogite from Sanbagawa belt, central Shikoku, Japan with the present experimental data, we found the content of ferric iron in quartz increases with increasing pressure and temperature:
lnXFe = (−1092 − 5.254T + 7.75P)/T,
where XFe, T and P are the number of Fe atoms in quartz per formula unit based on a 2-oxygen atom normalization (cationic mole fraction of Fe), temperature in Kelvin and pressure in kbar, respectively. This new geothermometer is applied to the ultrahigh-temperature metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica, resulting that the metamorphic temperatures are estimated as about 994-1095 °C for pressures 5-15 kbar.
This study documents contrasting style of melt-solid interaction during different stages of evolution from two samples of UHT aluminous granulites from the central part of the Proterozoic Eastern Ghats Belt, India. While the early phase melt (M1-melt) has largely been lost from the granulitic restite, the secondary melt (M2-melt) remained in-situ in both the rocks. The M1-melt is granitic in composition and was produced during the prograde heating stage when the rocks were evolving along an anticlockwise P-T path and could be documented from the sparse occurrence of quartz-plagioclase-perthite leucosome layers in the migmatitic aluminous granulites. The M2-melt, on the other hand was produced during retrograde decompressive stage, incipient in nature, and evidenced by the presence of undeformed symplectites consisting of cordierite-K-feldspar-quartz. Estimated melt chemistry shows peraluminous and ultrapotassic character. Such incipient melting possibly took place in presence of CO2-rich fluid during the post-peak decompressive stage and its possible interaction with the solid phases furnishes nature of crustal reworking during the post-Grenvillian age evolution of the lower crust.
We report fluid inclusion data on ultrahigh-temperature (UHT) granulites from Kumiloothu in the northern Madurai Block situated along the Palghat-Cauvery Shear Zone system in southern India. Three categories of fluid inclusions have been observed: primary inclusions in garnet comprising the dominant category, secondary inclusions in garnet, and rare primary inclusions in rutile and apatite enclosed within garnet. The melting temperatures of all the categories of inclusions lie in the narrow range of −57.0 to −56.6 °C, close to the triple point of pure CO2. Most of the fluid inclusions homogenize into the liquid phase between a temperature range of +11.3 to +30.3 °C, corresponding to low-CO2 densities of 0.59-0.85 g/cm3. Slightly higher density of 0.95 g/cm3 was obtained from a primary inclusion in rutile that homogenized at −3.6 °C. The fluid densities, when computed into isochores, indicate lower pressures (∼ 6.6 kbar at 1000 °C) than the peak P-T conditions (T >1000 °C at ∼ 8 kbar) estimated for this region. The results of this study, together with the primary nature of the inclusions trapped in high-grade minerals, indicates density reversal of peak metamorphic fluid, a common feature for many UHT granulites along the Gondwana suture zone as well as other UHT terranes showing clockwise P-T history.
We report here the metamorphic P-T path for granulite-facies metapelites from the eastern part of the Trivandrum Granulite Block (TGB), southern India, and compare with the paths from the western part of the block as well as from other granulite blocks and shear zones in this region for understanding of exhumation history of the southern granulite terrane. The peak temperature condition of the eastern part (900-1000 °C) is almost consistent with that from the western part, suggesting regional ultrahigh-temperature (UHT) metamorphism throughout the TGB. However, there is a slight difference in peak pressure conditions between the eastern part (12 kbar) and the western part (10 kbar) estimated from different Zn content within spinel in equilibrium with quartz. Such P ∼ 12 kbar high-pressure event is consistent with that obtained from granulite-facies rocks further north in the Palghat-Cauvery Shear Zone system (PCSZ) and Madurai Granulite Block (MGB). The results therefore suggest that the TGB, MGB, and PCSZ underwent similar prograde high-pressure metamorphism followed by peak UHT event along a clockwise P-T trajectory, related to the collisional orogeny during the assembly of the Gondwana Supercontinent.
Thorianite (ThO2) was found in the phlogopite-bearing spinel-garnet peridotite (Plešovice peridotite) occurring as decimeter-size lenticular body in the Gföhl granulite that forms the metamorphic core of the Variscan orogenic belt. Thorianite occurs as a member of multiphase solid inclusions, consisting of phlogopite + carbonates + apatite + graphite + rutile + monazite + thorianite, in chromian spinel. U-Th-Pb ages of the thorianite give a good concentration at 333.8 ± 4.5 Ma, which overlaps the U-Pb ages of zircon extracted from the host Gföhl granulite, probably reflecting the Variscan high-pressure high-temperature metamorphism during the continent-continent collision.
The metamorphic rocks exposed in the Sefuri and Tenzan areas, northwestern Kyushu, are composed mainly of mafic rocks with trace amounts of pelitic, ultramafic and calc-silicate rocks and crystalline limestone occurring as lenses or blocks. These rocks underwent regional metamorphism prior to the Cretaceous intrusive rocks. The metamorphic rocks in the Tenzan area, south of the Sefuri area, underwent amphibolite-facies metamorphism and estimated metamorphic P-T conditions of these rocks reach up to 700 °C and 4.0 kbar. On the other hand, the metamorphic conditions in the Sefuri area have been reported to be up to 850 °C and 5.5 kbar. The metamorphic P-T-t path of northwestern Kyushu is interpreted as a clockwise trajectory. These P-T conditions and lithological features suggest that the metamorphic rocks of northwestern Kyushu can be correlated with those of the Higo metamorphic terrane, which is thought to be a candidate of the eastern extension of collision zone between the North China and the South China cratons during Late Permian to the Triassic periods.
The following are errata for the letter entitled “Elastic wave velocities and Raman shift of MORB glass at high pressures” by Yoshio KONO, Hiroaki OHFUJI, Yuji HIGO, Akihiro YAMADA, Toru INOUE, Tetsuo IRIFUNE and Ken-ichi FUNAKOSHI (Vol. 103, no. 2, 126-130, 2008).
Page 127, column 1, line 8: Higo et al. (2007) should read Higo et al. (2008). Page 130, column 1, line 10: (2007) should read (2008). line 13: ‘in press’ should read 166, 167-174.
The following is an erratum for the original article entitled “K-Ar ages of high-magnesian andesite lavas from northern Kyushu, Japan” by Masaya MIYOSHI, Takashi NASU, Toshihiko TAJIMA, Michio KIDO, Yasushi MORI, Toshiaki HASENAKA, Hidetoshi SHIBUYA and Keisuke NAGAO (Vol. 103, no. 3, 183-191, 2008).
Page 187: Part of Table 2 was printed incorrectly. The following PDF shows the correct version.
The following are errata for the original article entitled “Critical cooling rates for glass formation in levitated Mg2SiO4-MgSiO3 chondrule melts” by Ken NAGASHIMA, Yoshinobu MORIUCHI, Katsuo TSUKAMOTO, Kyoko K. TANAKA and Hidekazu KOBATAKE (Vol. 103, no. 3, 204-208, 2008).
Page 208, in the References section, column 1 Line 10: “Kitamura, N., M., Sato, T., Hamai, M., Mogi, I., Awaji, S., Watanabe, K. and Motokawa, M. (2001) Journal of Non-Crystalline Solids, 293-295, 624-629.” should read “Kitamura, N., Makihara, M., Sato, T., Hamai, M., Mogi, I., Awaji, S., Watanabe, K. and Motokawa, M. (2001) Glass spheres produced by magnetic levitation method. Journal of Non-Crystalline Solids, 293-295, 624-629.”
Line 19: “Mukherjee, S., Zhou, Z., Johnson, W.L. and Rhim, W. Journal of Non-Crystalline Solids, 337, 21-28.” should read “Mukherjee, S., Zhou, Z., Johnson, W.L. and Rhim, W. (2004) Thermophysical properties of Ni-Nb and Ni-Nb-Sn bulk metallic glass-forming melts by containerless electrostatic levitation processing. Journal of Non-Crystalline Solids, 337, 21-28.”