摘要:

Hydrothermal synthesis of Fe‐pum‐pellyites was conducted using high pressure cold‐seal apparatus and solid oxygen buffering techniques at temperatures between 250°C and 550°C and 2.0–9.1 kbar Pfluid. Fe‐pumpellyites were synthesized from partially crystalline gel mixtures of compositions: 4CaO ‐ 2.1Al2O3_1.5FeO ‐ 0.3MgO ‐ 6SiO2(II) and 3CaO ‐ 1.5 Al2O3‐ 2.7FeO ‐ 0.3MgO ‐ 6SiO2(III) in the presence of excess H2O at Pfluidof 5–9.1 Kbar, temperatures between 275°C and 325°C, and fO2defined by the QFM and HM buffers; for both of these compositions (II and III), the condensed synthetic run products included minor 7Å chlorite ± garnet ± Fe‐oxide. The cell dimensions and aggregate refractive index (a= 19.13(2)Å,b= 5.940(4)Å,c= 8.847(5)Å, ±= 97.37(6)±, andn= 1.702(2)) of the pum‐pellyite synthesized from the bulk composition II mix are compatible with those of natural pumpellyites containing similar total Fe contents. Attempts at synthesizing Fe‐pumpellyites from a Mg‐free bulk composition were not successful; these results are consistent with the total absence of natural Mg‐free pumpellyites.The higher temperature, higher oxygen fugacity assemblages of the equivalent bulk compositions (II and III) consist of epidote ± minor amounts of chlorite, garnet, quartz, hematite, and magnetite. The results of these synthesis experiments accord with the mineral parageneses observed in low‐grade metabasites which imply that Fe‐pumpellyites are replaced by epidote with increasing temperature and/or fO2and that Fe3+is preferentially partitioned into epidote with respect to coexisting pum‐pellyite. In addition, these synthesis experiments indicate that Fe‐bearing pumpellyites crystallize at and are stable to lower temperatures than more aluminous pu

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1983.tb00266.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The Gran Paradiso basement complex of the French and Italian Alps is composed of metasediments, termed the gneiss minuti, and metabasic rocks, both of which are intruded by a late Hercynian granite. The Bonneval gneiss, which crops out at the western edge of the complex, is composed of highly deformed metasediments, volcanics and volcaniclastic rocks. Eclogites, now highly altered, occur in the metabasic rocks. Kyanite and blue‐green amphibole are locally present in the gneiss minuti and aegirine plus riebeckite occur in the Bonneval gneiss. A moderately high pressure ‐ low temperature metamorphic event of probable Alpine age occurred in the basement complex. This metamorphic event differs from that in the overlying Sesia unit and ophiolites of the Schistes lustrés nappe in being at lower pressures (below the ab = jd100+ qz transition) and post‐dating the major (D2A) deformation. The origin of the metamorphism is discussed and interpreted as a probable consequence of the overlying nappe pile which was emplaced during the D2Aevent. Subsequent greenschist facies metamorphism in the basement complex is a consequence of thermal relaxation during

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1983.tb00267.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The structure, microstructure and petrology of a small area close to the village of Bard in Val d'Aosta (Italy) has been studied in detail. The area lies across the contact between the Gneiss Minuti (GM) and the Eclogitic Micaschist (EMS) Complexes of the Lower element of the Sesia portion of the Sesia‐Lanzo Zone (Western Alps). Both complexes have undergone high‐pressure metamorphism, but the metamorphic assemblages indicate a sudden increase in pressure in going across the contact from the GM to the EMS. Therefore, we interpret the contact as a thrust dividing the lower element of the Sesia into two sub‐elements. This interpretation is supported by structural evidence.The early Alpine (90‐70 Ma) metamorphic history is best preserved in the EMS and is one of increasing pressure associated with thrusting. The maximum P/T recorded in the EMS is>1500 MPa (>15kbar) and 550°C and in the GM is<1500‐1300 MPa (<15‐13 kbar) and 500‐550°C. We suggest that the rocks were probably in an active Benioff zone during this time.From then on the histories of the GM and EMS are the same. Deformation continued and the thrust and thrust slices were folded during decreasing pressure. We interpret the first postthrusting deformation in terms of uplift associated with continued shortening of the crust and underplating after the Benioff zone had become inactive and a new Benioff zone had developed further to the north‐west.A still later deformation and the Lepontine metamorphism (38 Ma) are related to continued uplift. Much of this deformation is characterized by structures indicative of vertical shortening and lateral spreading as the mountains rose above the general lev

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1983.tb00268.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The oligoclase‐biotite zone of the Bessi area, central Shikoku is characterized by sodic plagioclase (XCa= 0.10–0.28)‐bearing assemblages in pelitic schists, and represents the highest‐grade zone of the Sanbagawa metamorphic terrain. Mineral assemblages in pelitic schists of this zone, all with quartz, sodic plagioclase, muscovite and clinozoisite (or zoisite), are garnet + biotite + chlorite + paragonite, garnet + biotite + hornblende + chlorite, and partial assemblages of these two types. Correlations between mineral compositions, mineral assemblages and mineral stability data assuming PH2O = Psolidsuggests that metamorphic conditions of this zone are about 610 ± 25°C and 10 ± 1 kbar.Based upon a comparative study of mineralogy and chemistry of pelitic schists in the oligoclase‐biotite zone of the Sanbagawa terrain with those in the New Caledonia omphacite zone as an example of a typical high‐pressure type of metamorphic belt and with those in a generalized‘upper staurolite zone’as an example of a medium‐pressure type of metamorphic belt, progressive assemblages within these three zones can be related

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1983.tb00269.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The rocks of the Scourian Complex have been intensively studied, but there is still no consensus as to the conditions of the granulite‐facies metamorphism preserved in these rocks. Recent estimates of these conditions fall into two groups, one at 820‐920°C andca.11 kbar and the second atca.1000°C and>12 kbar. Investigation of a variety of rocks shows that the recorded conditions vary with grain‐size, with higher‐grade conditions recorded by the cores of coarser (ca.10 mm) crystals, and lower‐grade conditions recorded by the rims of coarser grains and by finer grains. This observation suggests that re‐equilibration during recovery of these rocks to the surface has been important which may account for the discrepancy in estimated P‐T conditions. Revised estimates of the equilibration conditions of the Scourian Complex of T>1000°C and P>8.5 kbar are presented. The conditions suggested for the peak of metamorphism mean that the role of anatexis in the genesis of these rocks must be considered and the nature of the fluid phase thoroug

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1983.tb00270.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

In the Boi Massif of Western Timor the Mutis Complex, which is equivalent to the Lolotoi Complex of East Timor, is composed of two lithostratigraphical components: various basement schists and gneisses; and the dismembered remnants of an ophiolite. Cordierite‐bearing pelitic schists and gneisses carry an early mineral assemblage of biotite + garnet + plagioclase + Al‐silicate, but contain no prograde muscovite; sillimanite occurs in a textural mode which suggests that it replaced and pseudomorphed kyanite at an early stage and some specimens of pelitic schist contain tiny kyanite relics in plagioclase. Textural relations between, and mineral chemistries of, ferro‐magnesian phases in these pelitic chists and gneisses suggest that two discontinuous reactions and additional continuous compositional changes have been overstepped, possibly with concomitant anatexis, as a result of decrease in Ploadduring high temperature metamorphism. The simplified reactions are: garnet and/or biotite + sillimanite + quartz + cordierite + hercynite + ilmenite + excess components. P‐T conditions during the development of the early mineral assemblage in the pelitic gneisses are estimated to have been P + 10 kbar and T>750°C, based upon the plagioclase‐garnet‐Al‐silicate‐quartz geobarometer and the garnet‐biotite geothermometer. P‐T conditions during the subsequent development of cordierite‐bearing mineral assemblages in the pelitic gneisses are estimated to have been P + 5 kbar and T + 700°C with XH2O745°C and subsequent development of cordierite under conditions in the range P = 3‐4 kbar and T = 600‐700°C. The tectonic implications of these P‐T estimates are discussed and it is concluded that the P‐T path followed by these rocks was caused by decompression during rifting and synmetamorphic ophiolite emplacement resulting from processes during the initiation and development of a convergent plate junction located in Southeast Asia dur

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1983.tb00271.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY