Geochemical features of Meso-Neoproterozoic dolerite sills on the South-East margin of the Siberian Craton
EGU General Assembly 2020: Sharing Geoscience Online
Aleksandr D. Savelev ([email protected]); Andrei K. Khudoley ([email protected]);
1 INTRODUCTION 3 PETROGRAPHY Sergey V. Malyshev ([email protected]);
Meso-Neoproterozoic dolerite sills and dykes of the south-east margin of the Siberian Craton are A B commonly known as linked to the Sette-Daban LIP- related event. There are several U-Pb and Sm-Nd isochron 5 RESULTS isotopic dates for the rocks of the Ulakhanbam complex, giving a range of values from 930 to 1000 10 Ma. Although there is an overlap of several dates within error, sills become younger westward from DM 974-1005 Ma in the east part of the study area to C D 932-946 Ma in its west part. Due to wide range of 6 ages they likely represent at least 2 different magmatic events, although long event is possible εNd(t) as well. To resolve this issue, new accurate dates 4 are needed. 2 Photos of thin sections in transmitted light. Textural features of dolerites. (A) gabbroophitic, (B) GEOLOGY poikilophitic, (C) doleritic, (D) micropegmatitic. 0 2 900 950 Ma 1000 1050 In the result of the studying petrographic thin Values of ε (t) sections all the samples are classied as ne to Nd Arctic Ocean medium grained dolerites and quartz dolerites (grain size 0.2 to 2 mm). 1
GEOCHEMISTRY
4 Nb/Y ΔNb = -0.03 0.1 ΔNb = -0.06 Sakhara ΔNb = -0.0002 comendite Allakh-Yun’ East pantellerite Sea of 1 Allakh-Yun’ West Sakhara Iceland array Siberian Craton Yudoma Allakh-Yun’ East Okhotsk Allakh-Yun’ West Yudoma rhyolite phonolite 0.01 trachyte 1 10 0,1 Zr/Y rhyodacite Zr/Ti dacite trachy- andesite Nb/Y and Zr/Y variation in basalt from the neovolcanic andesite zones of Iceland and from normal segments of mid-ocean basanite ridges (N-MORB). The parallel lines mark the limits of 138° E alkali- nephelenite 0,01 andesite/ basalt the Iceland data (Fitton et al., 1997) basalt sub-alkaline Belaya basalt 30 2.5 0,01 0,1 1 10 100 UCC Sakhara Allakh-Yun’ East A N-MORB B 25 Allakh-Yun’ West Yudoma 2.0 Crustal Amga Nb/Y - contamination 20 - Diagram of Winchester (Winchester & Floyd, 1977) . 1.5 E-MORB - 15 -
(Th/Yb) PM HIMU 1.0 10 -
EMI, EMII (Nb/Th) PM - LCC 0.5 LCC Field of mantle-derived melts Sakhara 5 - - Allakh-Yun’ Enriched mantle sources UCC 1 0 0 settlement of 100 0 5 10 15 20 0 5 10 15 Ust’ - Maya A (Nb/Yb) PM (Th/Yb) PM 2 Mantle sources of the mac intrusions of Sette-Daban 3 event. Diagram A showing variations in (Nb/Yb)PM 60° N A B and (Th/Yb)PM ; Diagram B showing variations in Maya (Th/Yb)PM and (Nb/Th)PM ; Upper Continental Crust 10 (UCC) and Lower Continental Crust (LCC) Aldan Yudoma compositions are from Taylor and McLennan (1985), and enrichedmantle (EMI, EMII) and HIMU (high μ, 4 Sakhara OIB 238 204 Allakh-Yun’ East where μ= U/ Pb)mantle values are from Condie E-MORB Allakh-Yun’ West (2001). N-MORB 0 45 90 km Yudoma
1 9 Yukanda Chagda Gt-lherzolite A 2 anticline 3 anticline B La Ce Pr Nd Sm Eu Gd Tb Dy Ho Y Er Tm Yb Lu 2000 2000 Є1-2 ps+in 1% Є2um R mls Vjud 8 3 R3kn1 R3kn1 R3gr β’ R3 Є um 1000 Vjud Є2cs 2 R3kn1 R3gr 1000 Є2cs 0 0 1000 7 A 1000 R sl 1000 R3mls R3dz R3dl 3 β’ R R kn Є ps+in Vjud R sl R kn R kn β’ PZ 3 3 2 1-2 3 3 1 3 2 2 B 6 Map and geologocal Gt-Sp lherzolite Lithology 5 5% and sills positions cross-section legend: (Gt:Sp=50:50) 100 Phanerozoic rocks Sm/Yb 4 1%
Group Western Eastern Erathem
Formation plate plate Riphean and Vendian rocks 10% Thickness, m - 3 Main faults 5% 10% A B Subordinate faults 2 (A - map; B - cross-section) 10 Sp lherzolite 600 β’ PZ β’ R Dykes on cross-section 2 3 1 1%
Dalynda 5% A B Geological cross-section line 40% 10% 932±46 along the Allakh Yun' river 1 The main areas 0 of study of sills: 0 2 4 6 8 10 1 550 1 - Sakhara Rb K Ba Th U Ta Nb La Ce Pb Pr Sr P Nd Zr Hf Sm Eu Ti Gd Tb Dy Y Ho Er Tm Yb Lu 2 - Allakh-Yun' West (Yukanda)
Dzhoron 9 3 - Allakh-Yun' East (Chagda) Sakhara 4 - Yudoma Elements spidergrammes normalized (A) - to chondrite, 8 Allakh-Yun’ East (B) - to the primitive mantle (Sun & McDonough, 1989). Allakh-Yun’ West Yudoma Composite stratigraphic 7 B 1500 °C, 750 section legend:
Neoproterozoic CO = 0.5% 6 2 1450 °C
Ui Unсоnformity border FeO* 1500 °C
Malosakhara 20 kb
Dolerite sill Sakhara 5 1550 °C Sm/Yb 2 Allakh-Yun’ East Limestone 4 Allakh-Yun’ West 550 Dolomite Yudoma 15 kb
Kandyk 3 Sandstone Tholeiiticseries
Late Riphean Siltstone 2 Thin-layered
1 siltstone 10 kb Ti/50 1 Mudstone 900 Calc-alcaline series U-Pb age 1005±5 0 Kandyk (baddeleyite) 0 2 4 6 8 946±37 981±46 Sm-Nd age 942±18 1005±5 974±7 942±18 (isochron) Na2O + K2O MgO La/Sm A plot of Sm/Yb vs. La/Sm. (A) The shown melt curve 300 of spinel lherzolite and garnet lherzolite are calculated Gren Geological setting of OIB using non-modal batch melting equations of (Shaw, the study objects MORB 1970). Numbers along melting curves are the degree of 400 Mesoproterozoic and the composite Salar A B partial melting. (B) Depths and temperature conditions Maya stratigraphic IAB of melt formation (according to Savatenkov) 250 section of the Late El’dikan Riphean deposits in 50*Sm V 200 Vil’ Maya-Kyllakh zone 6 CONCLUSIONS
Combined with previous geological, petrological Ti and geochemical studies on the Sette-Daban event dolerites, the following conclusions can be drawn. (1) The Sette-Daban event is represented by a single C complex of rocks that has been formed over 50 million years, starting from 1 Ga. The complex isn't homogeneous, therefore, at different stages of its Zr development, it is represented by rocks of different chemical composition, reecting one riftogenic Diagrams for rocks of Sette-Daban event. geodynamic setting. (A) Discrimination diagram Na2O+K2O-FeO*-MgO (2) Geochemical characteristics disprove the plume (Kuno, 1968) (B) – Sm*50-Ti/50-V diagram origin of the complex; it is more likely to form as a (Vermeesch, 2006). Legend: OIB - oceanic islands result of stretching. basalt; IAB - island-arc basalt; MORB - mid-ocean The studies were supported by the Russian Science Mac sill on the point AS17-22 (Sakhara river, 2017) ridges basalt. (C) – Ti vs Zr diagram (Pearce,1982) Foundation project № 19-77-10048.