March 2015 LIP of the Month

The Yakutsk-Vilyui LIP of the Siberian Craton

Alexei V. Ivanov, Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia, aivanov@crust.irk.ru

Elena I. Demonterova, Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia, dem@crust.irk.ru

Vladimir E. Pavlov, Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia &³ Kazan Federal University, Kazan, Russia, pavlov-home@rambler.ru

Andrey V. Shatsillo, Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia, shatsillo@gmail.com

Boris B. Kochnev, A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia, KochnevBB@ipgg.sbras.ru

Introduction

The Siberian Craton is a structure composed of the Paleoarchean to Paleoproterozoic blocks, which were welded together during a Paleoproterozoic episode of magmatism and metamorphism that peaked at about 1.87 Ga (Gladkochub et al. 2006; Rojas-Agramonte et al. 2011). After that time, the Siberian Craton represented a single, large tectonic block, which was a constituent part of the supercontinents Nuna/Columbia (Paleoproterozoic), Rodinia (Mesoproterozoic) and Pangea (Paleozoic) and between the supercontinent cycles it acted as core of a separate continental block referred to as Siberian continent (Cocks and Torsvik, 2007; Li et al., 2008; Domeier and Torsvik, 2014).

In the Phanerozic, the Siberian Craton experienced large volume mafic magmatism at least twice, during Devonian (e.g., Kiselev et al., 2012) and Permian-Triassic (e.g., Ivanov et al., 2013). The Precambrian large igneous provinces on the Siberian Craton are inferred from mafic dyke records. Ernst (2007) argues that mafic/ultramafic dykes with average width of >10 m are indicators for being feeders of a flood basalt province. The Paleoproterozoic dykes are well known within the Siberian Craton (Gladkochub et al., 2010; Ernst et al. 2013; Ernst et al. 2014). Recent data indicates on a ~1 Ga mafic/ultramafic event within the Siberian craton (Ivanov et al., 2012; Savel’eva et al., in press).

The Permian-Triassic Siberian large igneous province is well studied (see http://www.largeigneousprovinces.org/04mar and Ivanov et al., 2013 for the latest review), though it remains enigmatic due to its anomalous size (~7×10⁶ km²) and volume (~4×10⁶ km³) even on the LIP scale (Bryan and Ernst, 2008; Ernst, 2014). The Precambrian large igneous provinces of the Siberian Craton, on contrary, are enigmatic due to poor preservation. The Devonian Yakutsk-Vilyui large igneous province (Y-V LIP) is eroded and its size is inferred from the dyke and sill distribution (Fig. 1). Here we summarize basic information about the Y-V LIP.

Chemistry

Major, trace element and Sr-Nd isotope data for few tens of samples was reported by Kiselev et al. (2012). Volcanic and intrusive rocks of the Y-V LIP are mainly low magnesium basalts of both the high- and low-Ti series. High-Ti basalts are predominant. Typical rock compositions are provided in the Table 1, whose primitive mantle (McDonough and Sun, 1995) normalized incompatible element spectra are shown in Fig. 2. Evolved rocks such as mugearites and benmoreites are also present. The limited compositional variability of the Y-V LIP could be an artefact of the insufficient sampling, however.

Geochronology

Geochronologic information is limited in literature. The published ages are mainly ⁴⁰Ar/³⁹Ar ages (Courtillot et al., 2010; Ricci et al., 2013; Kiselev et al., 2014) and only two U-Pb ages (Powerman et al., 2013).

The ⁴⁰Ar/³⁹Ar ages were obtained at three laboratories; namely at Berkeley Geochronology Center, Berkely, California, USA (Courtillot et al., 2010), at IDES geochronology laboratory, Université Paris-Sud, Orsay, France (Ricci et al., 2013) and at the Institute of the Earth’s Crust, Irkutsk, Russia (Kiselev et al., 2014). These laboratories used different standards and analytical (not always reported) protocols. Summary of the ⁴⁰Ar/³⁹Ar ages is provided in Table 2, where all ages are recalculated to the same age of 28.305 ± 0.036 Ma for the FC sanidine standard, which allows direct comparison to the U-Pb ages (Renne et al., 2010; 2011). All the ⁴⁰Ar/³⁹Ar ages were obtained on the samples from region within or close to the Vilyui rift. In addition we list one unpublished age obtained by the Irkutsk laboratory for a sample collected from a dyke from the northern part of the Y-V LIP (Fig. 1).

U-Pb dated samples are from the southern part of the Y-V LIP (Fig. 1). One of the two ages was obtained by the chemical abrasion TIMS (CA-TIMS) method with its ultimate precision. In total, nine grains were analyzed by this method among which six grains have shown inheritance of radiogenic lead, which is quite common for zircons from mafic intrusions, and were rejected from calculations. The weighted ²⁰⁶Pb/²³⁸U age on the three youngest grains is 377.72 ± 0.25 Ma (where error includes all analytical uncertainties but do not include errors from decay constants).

Another U-Pb age was obtained by the SHRIMP method. In total, eight grains were analyzed. Powerman et al. (2013) excluded from calculation of the age two youngest grains and suggested the ²⁰⁶Pb/²³⁸U age of 371.0 ± 3.3 Ma. However, large MSWD of 4.1 does not allow considering six grains used for the calculation as belonging to the same statistical distribution. If we assume that similar to the previous case the oldest U-Pb ages are due to inheritance and calculate the age only for the two youngest grains we obtain the mean ²⁰⁶Pb/²³⁸U age of 361.7 ± 2.2 Ma (Table 3).

In summary, available ⁴⁰Ar/³⁹Ar and U-Pb ages suggest long duration of the Y-V LIP.

Temporal relation to kimberlites

It has been shown that the Nyurba kimberltes were emplaced between the two pulses of mafic magmatism (Kiselev et al., 2014). Available U-Pb SHRIMP ages on perovskites from the Daldyn-Alakit kimberlites (Kinny et al., 1997) are plotted on the probability age histogram in Fig. 3. It seems that there is a tendency for kimberlites to erupt during quiescence of the mafic magmatism. Though, more precise dating of both the kimberlites and mafic intrusions is required.

Geodynamic setting

Fig. 4 shows paleogeographic reconstruction (Domeier and Torsvik, 2014) in Devonian (390 Ma) time, when the Siberian continent was bounded to the paleo-South by a subduction system involving recycling of the Rheic Ocean and to the paleo-North and to the paleo-West by spreading systems of the Mongolia-Okhotsk Ocean. However, further to the paleo-North and to the paleo-West there were other subduction systems and thus, in a broader sense, the Siberian continent was surrounded by the Devonian subduction systems from every side. Distances from the reconstructed paleo-arcs to the margins of the Y-V LIP varied from about 1 to 2 thousand km. In the late Devonian, the Siberian continent was characterized by another volcanic activity, named the Altai-Sayan Province (Vorontsov and Sandimirov, 2010; Vorontsov et al., 2013) located closer to the continental boundary (Fig. 1).

Models

Emplacement of diamond-bearing kimberlites after mafic volcanism requires the lithospheric mantle to be thick during and after the mafic Y-V LIP magmatism. Thickness of the lithospheric mantle of the Siberian Craton in the Devonian was estimated from PT data on the kimberlite-entrained mantle xenoliths to be 190-230 km depending on location (Griffin et al., 1999). Such thick lithosphere would prevent melting of a dry lower mantle plume right underneath the Y-V LIP (Ivanov, in press). There are three potential models, which can explain the Y-V LIP:

(1) Kiselev et al. (2012) note radial distribution of dykes and rifts and assume that they can be traced to the same plume centre located outside the Siberian Craton (Fig. 1, Fig. 4). According to that model, mafic melts laterally propagated for hundreds and thousands kilometers from an area of thin lithosphere into area of the thick cratonic lithosphere (Fig. 5) (Ernst, 2014).

(2) Ivanov (in press; http://www.mantleplumes.org/DLABook/Ivanov_Accepted.pdf) argues that melting occurred underneath cratonic lithosphere and was associated with deep (transition zone) dehydration of subducted slabs, similarly to a model suggested for the Permian-Triassic Siberian large igneous province (Ivanov and Litasov, 2014; see also a model of subduction associated asthenospheric flow of Wang et al., in press; http://www.mantleplumes.org/SupercontinentAssemblyLIPs.html).

(3) Another, not yet considered in literature for that particular large igneous province, model associates the Y-V LIP magmatism to the melting of fusible metasomatically modified by previous geologic processes lithospheric mantle (e.g., Puffer, 2001).

References