**3.2. Second stage: 120–105 Myr**

Jurassic—135–136 Myr; the formation of calc-alkaline complexes of rocks of andesite composition occurred at 120–105 Myr. One of the complexes is a fragment of the island arc which is preserved along the border of Mongol-Okhotsk orogenic belt on Russian territory (**Figure 2**) [7]. The formation of an intraplate volcano-plutonic complex of rhyolites-alkaline trachydacytes and their plutonic comagmatites occurred 101–99 Myr [3]. According to the geochronology data, the beginning of the fourth stage can be counted since 56 Myr till our time, practically. Impulsive outpouring of volcanites, predominantly of basic composition, occurs

The beginning of the magmatic activity of late Mesozoic is marked with the formation of trachyriolite volcanic complex. These are the rocks of Itikut complex located on Russian territory. It is represented by stratified volcanogenic-terrigenous formations and subvolcanic bodies [4, 16, 22]. Stratified formations perform rift-like depressions in the north–north eastern direction. The lower part of the cut is made with tuff terrigenous rocks. Belonging of the acid volcanites to the intraplate post-collisional formations is confirmed by petro-geochemical

According to the findings of macro- and micro-palaeoflora from the tuff-terrigenous part of the section of the cover part of the complex, the time interval might be stated as the end of Jurassic-Hauterivian [16]. The age of the volcanites of the Itikut complex is 135–136 Myr (40Ar/39Ar method) [37] by the geochronological data. According to these data, the time of the

**Figure 2.** Spatial position of the rocks of the volcano-plutonic Burunda complex, according to the data [7] and Mudanjianiang magmatic belt, according to data [31]. The rock of the Burinda volcano-plutonic complex—(1). Outline

of the northern flank Mudanjianiang belt—(2). Tectonic boundaries—(3).

Itikut complex rocks formation was accepted as the end of the Jurassic—135 Myr.

from this moment [2, 16].

36 Tectonics - Problems of Regional Settings

features of the rocks [4].

**3.1. First stage: late Jurassic to 135 Myr**

The most widely spread volcanic complexes are of andesite composition and were formed 120–105 Myr. Geochronological data on volcanites and plutonic comagmates of the complexes correspond to the 118–105 Myr interval [2, 5]. Considering the stage of the accumulation of tuff-terrigenous coagulation at the base of stratigraphic sections of these complexes and the presence of fossil biological remains of Aptian age in the sediments, the time interval of the rock forming of the complexes is stated as 120–105 Myr [5]. Three volcanic complexes of this age have been identified on Russian territory: Pojarka, Stanolir, and Burunda [5, 16]. Rocks of Burunda complex correspond to island-arc formations by the petrochemical and geochemical characteristics [7].

It can be stated that the island arc was formed in late Mesozoic along the northern margin of superterrane (on the border with the Mongolo-Okhotsk orogenic belt in modern coordinates). Nowadays, it represents a fragment of the island arc that lies at a significant depth (about 3000 km) of the coastal-marine sediments [5, 7] (**Figure 2**). Concerning this, highlighting of the Mudanjianiang belt is of interest in the region of the Burunda rock complex island-arc development (**Figure 1**).

Age data of the Mudanjianiang belt rocks are ambiguous, which is shown by the researchers [43]. But the authors state that these formations are the analog of Burunda volcano-plutonic island-arc complex. The age interval of formation for the magmatites of Burunda complex is stated by the precision (40Ar/39Ar, Rb-Sr) methods as 111–105 Myr [5].

The volcanic formations aged 118–105 Myr are widely developed within the Jiamusi terrain in China [2]. The authors subdivide the rocks into four formations here: Tuntianying—118–116Myr, Sanxianling—117–115 Myr, Huoshanyan—108 Myr, Jingouling—106 Myr. The affinity of these formations with the rocks of the volcanic complexes listed above that was studied in the territory of Bureya terrain (Russia) and is not only limited by age compatibility. This is confirmed by their petro- and geochemical affinity. The volcanites of the Jiamusi terrain are also moderately enriched in Sr., Zr, Hf, Ti, Y, REE and depleted in Ta and Nb according to [2].
