Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Dzhekonda (Dzhekondinskii)

stripes

Occurrence number: 
136-01-024
Country: 
Russia
Region: 
Aldan
Location: 
Longitude: 125.92, Latitude: 58.4
Carbonatite: 
No

A nearly circular complex about 4.5 km in diameter, Dzhekonda cuts through lower Cambrian dolomites. Caldera subsidence has preserved a sequence, up to 650 m thick, of alkaline extrusive rocks in which are rare intercalations of silicic argillites. The extrusive rocks are situated in the central area of the complex with intrusives occurring as incomplete marginal zones and a central intrusion. The extrusive rocks occupy approximately 80% of the area of the complex and are represented predominantly by peralkaline trachytes and analcime porphyries, with tuffs and tuff breccias of the same rock types. Melanite syenites, represented by an arc-like body up to 200 m wide on the eastern and northern edges of the complex, are the earliest intrusive rocks. They have a trachytic and sometimes porphyritic texture and may be medium- or coarse-grained. They are composed of K- feldspar (75-88%), melanite (up to 12%) and alkali amphibole with smaller quantities of nepheline and albite; relicts of non- alkaline pyroxene and basic plagioclase are present. In the central part of the complex the extrusives are cut by a stock- like body of augite syenites which have a markedly trachytic character. Microcline is the dominant phase (60-80%) together with prismatic aegirine-augite, albite, biotite and amphiboles, as well as accessory titanite, apatite, magnetite, zircon, baddeleyite, rutile and fluorite. The youngest intrusive rocks are pyroxene syenites/diorites which form a broad, up to nearly one kilometre wide, horseshoe-shaped body extending around the complex on the western, southern and northern sides as well as small dykes which cut Cambrian dolomites to the north. They are composed of plagioclase (An30-32) and K-feldspar, the feldspars making 50-60% of the rocks. The plagioclase is often zoned from andesine cores to oligoclase rims (An20-25) with more basic phenocrysts in some porphyritic rocks (up to bytownite). The mafic minerals are pyroxene (0-6%) and hornblende (0-6%); accessories include zircon, apatite, titanite, melanite, lamprophyllite and corundum. Numerous dykes of solvsbergite, aplite and leucocratic granosyenites are developed amongst the extrusive rocks. Xenoliths of dolomite included in the alkaline rocks are totally altered to skarns.

References: 

MAKSIMOV, Ye.P. 1973. Mesozoic annular magmatic complexes in the Aldan Shield. International Geology Review, 15: 46-56.
OSOKIN, E.D., LAPIN, A.V., KAPUSTIN, Yu.L., POHVISNEVA, E.A. and ALTUHOV, E.N. 1974. Alkaline provinces of Asia. Siberia-Pacific group. In L.S. Borodin (ed) Principal provinces and formations of alkaline rocks. 91-166. Nauka, Moscow.

Map: 
Fig. 2_230. Dzhekonda (after Maksimov, 1973, Fig. 2).
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith