 Tranomaro in 1991 >> |
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| Geographical division |
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| We will distinguish: |
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| 1 the volcanic solid mass of |
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| Androy, it is covered with |
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| thorny bush and meadows. |
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| 2 the gneissic zone of to |
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| Mandrarean Androy, fields |
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| plains and hills, rare zones |
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| of savanna on of red ground |
At the time |
| calcareous carapace. |
of the great |
| Altitude varies there from |
dryness in |
| 600 meters on the hills |
the south. |
| to 250 meters at the bottom. |
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| 3 the western slope of the high Anosyans |
| chains which tops are staged between |
 |
| 1500 and 2000 meters. It is a field of |
| meadows. |
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| Geological divisions. |
| 1 Crystalline schists. |
| Gneiss with diopside, syenitic eysies |
| gneisses, arteritic injections, gneiss at |
| cordierite, etc. |
| 2 Old eruptive rocks. |
| Pegmatites, Dissogénites, Esirians |
| granites , charnockites, kalambatreans |
| granites, late granites . |
| 3 Recent eruptive rocks. |
| (Volcanic solid mass of Androy) |
| a) A the base, a thick basaltic |
| subhorizontale series . |
| b) Basaltic dykes. On the road to Andranondambo |
| c) A thick higher subhorizontale rhyolitic series. |
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| d) Rhyolitic dykes . |
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| 4 Recent formations. |
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| If russet-red sands are excluded, the recent |
| formations have only a very weak development. |
| It is necessary to quote the alluvial plains of |
| Androtsy, Esira, Sangoria and Pisopiso. |
| A notable calcareous carapace covers most of the area. |
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| The anosyans granites are regarded as synorogenes, eocambrians |
| formed in the androyans series to which an age higher than 2400 MY |
| is allotted. |
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| The esirians granites present very variable crushings of intensity which |
| often give them a gneissic facies . |
| Sometimes, there is passage to orthogneisses. General foliation is sub meridian. |
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| The occurrences of the Andranondambo area were industrially exploited since 1993 and have been |
| almost abandoned few years later. This, because of difficulties to exploit sapphire direct in the |
| bedrock, usually corundum is not concentrated enough. Furthermore, the hardness of the |
| rock makes its exploitation very expensive. |
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|
 All of the pictures on this website have been shot by gggems.com |
| Text written by Alain Darbellay. |
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| © 1987 - 2021 GGGems, All rights reserved. |
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The story
