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