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Y. Majigsuren, A. Kitakaze and S. Jargalan
I. Western Khubsugul II. Eastern Khubsugul III. Tesiin gol IV. Khanui gol V. Orkhon-Selenge VI. Ugii nuur VII. Tariat-Chuluut VIII. Southern Khangai IX. Dolina-Ozer X. Baruun khuurai XI.Dzabkhan. XII.Gobi Altai XIII. North Gobi XIV. Mandal Gobi XV. Undurshil XVI. Dariganga XVII. Khalkhiin gol
XVII
XIV
VIIXI
XIII
VIII
IX
X
XII XV
XVI
II
III IVV
VI
I
XVIIUlaanbaatar
Mandal Gobi
XI
Tariat
Shavariin tsaram
Tariat sumTerkhiin tsagaan nuur
1PZ
D1tr
1dz
N-Q
PZ
N-Q
PZ 1
Q
D1tr
1PZ
1PZ
D1tr
1dz
N-Q
PZ
N-Q
PZ 1
Q
D1tr
1PZ
Quaternary sediments
Olivine basalt
Volcanic conus
Late Paleozoic gabbro, gabbrodiorite, diorite & granite
Lower Paleazoic rhyolite porphyry, andezite porphyre, their tuff,
Lower Devonian Tariat formation -conglomerate, sandstone, siltstone
tuff conglomerate, tuff sandstone, tuff siltstone.
Lower Paleozoic Dzag series - sedimentary metamorphic rock
Legend
Quaternary sediments
D 1
Dolerite
tr
N-Q
Pyrope, sanidine, olivine bearing
Lower Devonian Tariat formationconglomerate & sandstone
pyroclastic rocks
Olivine basalt
D1 trD1tr
D
Mandalgobi
K1
EK
P
E NP
Mandalgobi
P
1
11
1
1
Volcanic conus
Paleiogenic basalt
biotite granite, granodiorite
Neoproterozoic limestone
Early Permian amphybole
Cretaceous sedimentry rock
Pyroxene Sanidine
OlivinePyrope
Mandalgobi-basalt. Macrocrystals of biotite in melanocratic fine phenocrysts groundmass.
Shavariin -Tsaram lherzolite. Altered garnet, brown spinel and
clinopyroxene in the groundmass.
Mandalgobi basalt. Contact of garnet dark glassy volcanic showing some
macroxenocrysts and fine phenocrysts
Shavariin Tsaram basalts. The macrocrystals include orthopyroxenes of enstatite, garnet, plagioclase and
xenolyths of host rock.
Mandalgobi basalts. Ground mass of limburgite basalt, showing feldspar microlites, or glassy groundmass. The macrocrystals
include pyroxene, olivine and apatite.
Euhedral phenocrysts of magnesium –rich olivine and more iron rich olivine occur on the rims of the phenocrysts and the groundmass. Chemical composition of olivine varies from Fo68.5 to Fo99.6. Olivines in Shavariin-Tsaram basalt
(Fo69-Fo99.6) show higher Fo content comparing to Mandalgobi basalt
(Fo69.5-Fo90.7).
Pyroxenes are mostly in groundmass in Shavariin-Tsaram basalt, and in phenocryst and groundmass in Mandalgobi basalt. Pyroxenes are mostly diopside, and some of them are enstatite in composition. No compositional difference observed between pyroxene in Shavariin-Tsaram basalt and Mandalgobi basalt.
Diopside Hedenbergite
Enstatite Ferrosilite
Plagioclases are in phenocryst and groundmass. Plagioclace varies in composition
Ab
An
Or
Cr2O3 TiO2
CaO
Xenocrysts of red to dark red colored garnet (pyrope) occur only in Shavariin Tsaram basalt. Pyrope is very low TiO2 and Cr2O3. Cr2O3 below levels typical of diamondiferous kimberlite or lamproite. CaO levels too high for the given Cr2O3 values for diamondiferous source.
0
2
4
6
8
10
12
14
16
40 5 0 60 70 80
P h on ol i te
T ep h r i p h on ol i t eT r ach y te
&T r a ch y da ci te
F oid i te
P h onot eph r i te
T eph r i te&
B a sa n i te
P ic r oba sa l t
B a s a l t B a sa l t i ca n desi t e
A n desi te
D a ci t e
T r ach yba sa l t
R h y ol i te
U l tr aba sic B a sic I n term ediate A cidSiO2 wt%
Tas Diagram
Shavar Tsaram basalt is picritic basalt in composition, while Mandalgobi basalt is basaltic andesite.
Geochemistry of basaltic rock shows that they are high potassium calc alkaline and composition. SiO2 content varies from 48.8 to 50.7-wt%, while it ranges from 44.2 to 45.8 wt% in Mandalgobi basalt.
0
2
4
6
K 2O
H igh K ca lc-a lk a l ine
M edium K ca lc-a lk a lin e
44 48 52 56 60 64
Major element variation diagrams for the Shavariin–Tsaram and Mandalgobi basalts. Basalts Shavariin-Tsaram having lower TiO2, Fe2O3, MgO, CaO and higher Al2O3 and Na2O than Mandalgobi basalts.
On MORB normalized trace element spider diagram show basaltic rocks of two areas show similar characteristics. Rocks are enriched in LILE and almost similar to similar with MORB value in HFSE
100
10
1.0
0.1Sr Rb Ba Nb Zr Y Cr