Within the summit areas of the Rogacz Massif, located east of Wojcieszów, there are numerous rock outcrops. These formations have a very interesting geological history. They constitute a fragment of the volcanic complex, which is a building element of the Kaczawskie Mountains and Foothills. This formation is called the trachyte complex from Lubrza. Within it, as the name suggests, there are trachytes, which are neutral volcanic rocks. The term “neutral” is used for rocks containing 53 to 65% silica (SiO2). The second component of the trachyte complex in Lubrza consists of volcaniclastic rocks, which are sedimentary rocks composed of fragments of volcanic rocks. These rocks underwent metamorphic transformations under the influence of high temperatures from lava. The zone of these changes is called a contact aureole. The rocks of the trachyte complex in Lubrza are the result of submarine volcanism associated with the rifting of the oceanic crust. Such underwater rifting, from which lava is extruded, is referred to as a rift zone. Geochemical studies have indicated that the source of the magma was the Earth’s mantle. According to the theory of plate tectonics, which explains the formation and breakup of continents and oceans, diverging plates at a rift zone gave rise to the Rheic Ocean. All of this took place at the Cambrian-Ordovician boundary.
On the southern slope of Rogacz, slightly below the summit, predominantly volcaniclastic rocks with well-defined lamination are found. These rocks exhibit alternating bands (laminae) of dark and light layers. Some of them, with cream and dark gray hues, have a thickness ranging from 1 to 4 mm. However, the prevailing rocks have thicker laminae, ranging from 0.5 to approximately 2 cm. They exhibit various colours, with black layers most commonly occurring alongside laminae of gray-green or gray-red hues. The red colour is associated with the oxidation of ore minerals. The black laminae come in two types. The first type is primarily composed of chlorite, while the second type consists mainly of sericite. The light laminae are composed of grains of albite and carbonate. In addition to the light laminae, there are also several millimetre-sized lenses found in many places, mainly composed of albite, carbonates, as well as epidote and amphibole. The primary rocks were deposited in a marine environment and subsequently underwent metamorphic processes, including contact metamorphism.
In addition to laminated rocks, in the upper part of the profile, there are dark green, aphanitic rocks within which one can distinguish clasts (fragments) of lava. There is also a variety of dark gray rock here, speckled with pink spots – these are very small (about 0.3 mm) garnets.
The described rocks extend over a length of approximately 50 metres. Their height reaches up to 20 metres.
The name “trachyte complex of Lubrza” is closely associated with the nearby Lubrza hill. It is precisely there that a model example of such rocks has been described. Therefore, this name is used for all locations where such rocks are found. In geology, names for formations are often derived based on the location where a stratotype is present, which is the most typical and representative example of a particular geological unit.
