| TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL) |
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| 作者姓名： | E.Schill\ E.Appel\ P.Gautam\ [WT ”BX] |
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| 作者单位： | 1.Institut für Geologie und Pal ontologie，Universitet Tübingen，Sigwartstrasse 10，72076 Tübingen，Germany;2.Central Department of Geology，Tribhuvan University，Kirtipur，Kathmandu，Nepal |
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| 摘 要： | TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL)1 AppelE ,M櫣ｌｌｅｒＲ ,WidderRW .PalaeomagneticresultsfromtheTibetanSedimentarySeriesoftheManangarea (northcentralnepal) J].GeophysJInt ,1991,10 4:2 5 5～ 2 6 6 .
2 AppelE ,PatzeltA ,ChoukerC .SecondarypalaeoremanenceofTethyansedimentsfromtheZanskarRange (NWHimalaya)J].GeophysJInt,1995 ,12 2 :2 2 7～ 2 42 .
3 B…
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TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL) |
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| E.Schill,et al.TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL)[J].Earth Science Frontiers,2000(Z1). |
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| Authors: | ESchill |
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| Abstract: | In Mesozoic carbonates of the Tethyan Himalayas two characteristic remanent magnetisations(ChRM\-1 and ChRM\-2)were identified by their unblocking spectra.The ChRM\-1 is carried by pyrrhotite(unblocking spectra:270～340℃),acquired as a secondary thermoremanent magnetisation (TRM) during exhumation and cooling.The ChRM\-2 is carried by magnetite (unblocking spectra:430～580℃).A primary origin is indicated by calcite twin geothermometry and remanences consistent with the expected direction.Along an E—W profile of 10km length the ratio of remanence intensity of pyrrhotite to magnetite ( R PYR/MAG )changes systematically (from 0 38 to 1 00,Fig.1).It is known that pyrrhotite is formed in marly carbonates during low\|grade metamorphism (Rochette 1987).This occurs at the expense of magnetite.Thus the ratio R PYR/MAG is related to metamorphic temperatures and can be used as a geothermometer for temperatures≤300℃ in low\|grade metamorphic carbonates where other methods are rare.Stable remanence directions were used to estimate the amount of block rotation around vertical and horizontal axes(i.e.Klootwijk et al.1985,Appel et al.1991 & 1995).In the Shiar area the pyrrhotite remanence directions follow a small\|circle distribution with a best fit parallel to the N—S direction(Fig.2). |
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| Keywords: | palaeomagnetism Tethyan Himalayas block rotation geoghermormetry |
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