Decay Process of Serpentinite: The Case of the San Giovanni Baptistery (Florence, Italy) Pavement

Serpentinite is a low-grade metamorphic rock derived from the transformation of ultramafic rocks. Mainly because of its aesthetic characteristics it has been widely used as a building and ornamental stone. “Verde di Prato” is the most common local name used in Tuscany to refer to this type of rock, historically quarried in this area and used for many centuries in a large number of monuments of this region. In this paper, we report the results of a study carried out on the serpentinite from the pavement of the Florence baptistery, to properly characterize it from a physical point of view, describe the rock conservation state, and understand the phenomena responsible for its decay. The studied rock displays numerous forms of decay including fractures, loss of material, erosion, discolouration and efflorescence. X-ray diffractometer analyses of the efflorescence revealed the presence of numerous salts whose formation can be imputed to multiple, possibly concomitant, causes such as the high relative humidity and the variation of inside temperature, the presence of concrete and/or cementitious mortars in the subsoil, atmospheric pollution and the burial ground existing close the baptistery.

Spatial distribution prediction of pre-Sinian volcanic and metamorphic rocks in Xinhenan-Sandaoqiao area, Northern Tarim Basin

The main type of oil and gas reservoir in the Xinhenan-Sandaoqiao area is buried hills. The distribution pattern and scale of reservoirs are obviously controlled by pre-Sinian basement strata. However, the lithologic combination and spatial distribution pattern of pre-Sinian basement in this area are still unclear. In this paper, the spatial distribution of pre-Sinian basement volcanic and metamorphic rocks is studied by using the method of multifactor comprehensive analysis. Firstly, the lithology and lithologic combination of igneous and metamorphic rocks are determined according to cores and thin sections. Guided by the seismic reflection characteristics of different lithologic combinations, different lithologic combinations are identified on the profile by combining the seismic reflection characteristics of single well and multiwell. Secondly, using cluster analysis technology, three seismic attributes sensitive to lithology are selected from 10 attributes, crossplots of three seismic attribute values are constructed, and the distribution range of attribute values corresponding to different lithologic combinations is defined for plane lithologic identification. Finally, the plane lithology distribution of the surface layer of pre-Sinian basement is described by combining plane and profile. Six distribution types were identified: deep metamorphic bedrock area in Kuqu depression, dynamic mixed metamorphic rock and intermediate-acidic intrusive rock area, metamorphic bedrock in thrust napple slopes area, thermal contact metamorphic rock area, intermediate-acidic intrusive rock area, dynamic metamorphic rock area and gneiss area in faulted uplift core.

Study on the Geohazard Distribution Laws and Hazard-Causing Mechanism in Menghai County of Yunnan Province

study area is located at the southwest border of Yunnan Province and the southward extended part of Nushan Mountain, with complex and fragile geo-environmental conditions. Deep geological survey and mathematical analytical investigation on the geohazard distribution and hazard-causing mechanisms in this area were carried out in this study. The results revealed that: (1) The development of geohazards was affected differently by different slope shapes, slope structures and elevations; (2) Most of the geohazards were developed in medium shallow cut ridge-like medium-height mountainous geomorphological region and shallow cut steamed bun-like low and medium-height mountainous geomorphological region, and they were relatively concentrated on tectonic zones like fault zones; (3) The slopes formed by loose earth piling up on the surface of Indo-Chinese magmatic rock and Lancang Group metamorphic rock formations were most prone to slope instability and even landslide. The deep study on the geohazard distribution and hazard-causing mechanisms can provide geoscientific basis and reference for the prevention and mitigation work of geohazards under similar geo-environmental conditions.

Semiquantitative Characterizations And Controlling Factors of Microscopic Pore Characteristics of The Metamorphic Rock Reservoir In The Central Paleo-Uplift Belt, Songliao Basin

Currently, metamorphic rock is a common target for oil and gas exploration, and reservoirs are the key factors restricting hydrocarbon exploration and development in metamorphic rocks. The deep metamorphic rock gas reservoir in the central paleo-uplift of the northern Songliao Basin has good exploration and development potential. In this study, we use a combination of qualitative descriptions and quantitative analysis to comprehensively analyze the pore characteristics of the reservoir and explore the factors controlling the pore characteristics of the metamorphic rock reservoir in the central paleo-uplift belt of the Songliao Basin. The metamorphic rock reservoir in the central paleo-uplift belt contains three types of lithologies: chlorite schist, mylonite, and mica schist, each with different protoliths and metamorphic histories. The reservoir space can be divided into 4 pore types, and the reservoir space of each lithology is quite different. The results of high-pressure mercury intrusion and nitrogen adsorption indicate that the pore size distributions of the schist and mylonite differ. Compared with the schist, the mylonite has less reservoir space, stronger homogeneity, larger pore size, smaller specific surface area, more natural gas reservoir space and stronger natural gas adsorption capacity. This paper also studies the formation process of the reservoir and divides it into four stages. Finally, this article discusses in detail the factors controlling the microscopic pore characteristics of metamorphic rock reservoirs in the central paleo-uplift belt; the metamorphic rock protolith is the most important controlling factor.

On the article “Weathered potassic volcanic rocks as protoliths of the hematitic phyllites of the southern Serra do Espinhaço (MinasGerais)”: a discussion

Chaves and Knauer (2020) have presented three new whole-rock chemical analyses of phyllitic hematite, a unique metamorphic rock of the southern Serra do Espinhaço. Based on their three samples and a selection of other three samples from the literature, Chaves and Knauer have proposed that the geochemical uniqueness of the rock – i.e., high contents of K2O, Al2O3 and Fe2O3, and depletion in SiO2 – would represent a weathered, feldspathoid-rich alkaline basalt. This contribution is a discussion of their new data, the trace-element contents of which are at odds with those of a potassic, mantle-derived volcanic protolith for the hematitic phyllite. Its Nb/Th ratios of ~3 and chondrite-normalised La/Yb ratios of ~9–17, for instance, are typical of the continental crust. We also point out aspects that escaped the attention of Chaves and Knauer (2020), one of which is the ubiquitous occurrence of tourmaline in the hematitic phyllite.