RECOGNITION OF A 600-KM-LONG LATE TRIASSIC RARE METAL (Li-Rb-Be-Nb-Ta) PEGMATITE BELT IN THE WESTERN KUNLUN OROGENIC BELT, WESTERN CHINA

The rising demand of strategic metals, especially lithium, necessitates discovery of new resources to meet the global supply chain. Recently, several pegmatite-hosted rare metal (Li-Rb-Be-Nb-Ta) deposits have been discovered in the Western Kunlun orogenic belt, making it a new world-class rare metal resource (estimated ~7 Mt Li2O and 0.16 Mt BeO). Understanding the metallogenesis of this belt is critical to further evaluate the rare metal potential. In this study, columbite-tantalite (coltan) and monazite from rare metal pegmatites and zircon from potential parental granites were collected from five representative rare metal pegmatite deposits in the western, middle, and eastern parts of the Western Kunlun orogenic belt for U-Pb geochronology. The results indicate that despite the distances of the sampling localities in different parts of the Western Kunlun orogenic belt, the ages of pegmatite-hosted rare metal mineralization fall in a narrow range of ca. 208–204 Ma. These rare metal pegmatites are temporally and spatially related to adjacent postorogenic granites emplaced following the closure of the Paleo-Tethys Ocean. The compositional characteristics of K-feldspar, biotite, and muscovite of the granites and pegmatites, along with regional mineralogical and textural zonation of the pegmatites, suggest that the rare metal pegmatites were derived from the volumetrically much more important, highly fractionated granitic intrusions. We propose that, in combination with the data from previous studies, the 218–204 Ma interval represents a newly recognized rare metal metallogenic period linked with granitic intrusions in the Western Kunlun orogenic belt, revealing a 600-km-long late Triassic rare metal pegmatite belt composed of multiple ore fields formed in a similar metallogenic setting. These results emphasize the importance of identifying fertile, Late Triassic to Early Jurassic granitic intrusions for rare metal pegmatite exploration. Furthermore, combined with recent studies on the Songpan-Ganzi rare metal pegmatite belt along the eastern segment of the Paleo-Tethys, this study further highlights the great potential of rare metal resources in this global tectonic zone.

New Evidence of the Brizziite, Sodium Antimonate from the Central Paratethys Sea Strata in Poland

Brizziite, a rare sodium antimonate (NaSb5+O3), and fluorcalcioroméite ((Ca,Na)2Sb5+2O6F), have been identified in two boreholes (Pasternik and Włosienica) which are situated 50 km apart. Both wells are located west of Krakow, Poland, and were drilled in the Miocene strata of the Paratethys Sea (a remnant of the Tethys Ocean). The Sb minerals are scattered in a solidified light blue silica gel within marls and layered clays. They occur most often as anhedral grains up to 20 μm in size. The presence of these phases was confirmed by Raman spectroscopy (RS) and X-ray diffraction (XRD). The brizziite from this study represents a secondary mineral after the alteration of roméite within a supergene zone, or crystallization from Sb-rich solutions derived by the leaching of the weathered primary roméite. Hence, the calcium and fluorine admixtures in their composition, determined by EPMA, indicate intergrowths of brizziite and roméite on the micro- to crypto-scale. The presence of the antimony in the study area is related to rejuvenated Old-Paleozoic polymetallic ore-mineralization occurring in the basement of the Krakow-Silesia Monocline. The phenomenon of the repeatability of brizziite in Pasternik and Włosienica, distant by several tens of kilometers, can be explained by the following three steps: (i) the penetration of the chloride ions from the drying up seawaters of the Paratethys Sea into the Miocene groundwater system, (ii) the mobilization of Sb5+ in the form of chloride complexes, and, finally, (iii) the transportation of the Sb-bearing solutions within the marly and clay sediments.

The dire straits of Paratethys: Gateways to the anoxic giant of Eurasia

A complex interplay of palaeoclimatic, eustatic and tectonic processes led to fragmentation and dissipation of the vast Tethys Ocean in Eocene-Oligocene times. The resulting Paratethys Sea occupied the northern Tethys region on Eurasia, grouping water masses of various subbasins, separated from each other and from the open ocean through narrow and shallow gateways and land bridges. Changes in marine gateway configuration and intra-basinal connectivity affected the regional hydrology, shifting most Paratethyan basins to extreme carbon-sink anoxic environments, anomalohaline evaporitic or brackish conditions or even endorheic lakes. Paratethys gateway restriction triggered the onset of a long-lasting (∼20 Myr) giant anoxic sea, characterised by stratified water masses and anoxic bottom water conditions, resulting in thick hydrocarbon source rocks. Here, we review the geological evolution of the “dire straits” of Paratethys that played a crucial role in the Eocene-Oligocene connectivity history of the Central Eurasian seas and we show that the main anoxic phases (Kuma and Maikop) correspond to restricted connectivity with the global ocean and a period of CO2 depletion in the atmosphere. Paratethys represents one of the largest carbon sinks of Earth's history and may thus have played a prominent role in global climate change.

Diagenesis of Palaeozoic-Mesozoic Tethys Ocean Carbonate succession- Oman Mountains

This paper studies the uppermost unit of Kharus Formation (Cambrian) and the Autochthonous Akhdar Group (Permian-Triassic), which unconformably covers the pre-Permian strata. The petrographic and geochemical as well as field observations indicate that the succession underwent different stages of dolomitization that produced rocks inheriting the original host rock textures and structures (fabric-preserving dolomitization) and rocks with complete obliteration of the pre-existing textures (fabric-destroying dolomitization). Dolomites that retain the original fabric of the limestone are indicators of the host rock mineralogy, i.e., whether it was made up of high Mg-calcite or aragonitic allochems and indicate early dolomitization. The top part of the Kharus Formation consists of pervasively dolomitized units, whereas dolomites belonging to the Autochthonous Akhdar Group display variable degrees of structural and textural preservation. The evidence suggests very early dolomitization in a relatively short time interval for the Permian-Triassic carbonates. The preserved depositional features in the Permian-Triassic carbonates indicate deposition in shallow marine environments with variable energy levels. Seven facies are inferred: stromatolites, mudstones, wackestones, intraformational breccias, grainstones, packstones and grain/packstones. Petrographic as well as field observations exclude evidence of evaporites within Palaeozoic-Mesozoic rocks. Five paragenetic phases are determined to explain the type of dolomitization and to indicate the type and severity of diagenesis that affected the Palaeozoic-Mesozoic Tethys Ocean carbonates from the Oman Mountains.

A new genus of prosopid crabs (Decapoda: Brachyura: Dromiacea) from the Upper Jurassic of southern Germany

A new monotypic genus and species of brachyurans, Petersbuchia thauckei n. gen. n. sp., is described from southern Germany. The holotype, an incompletely preserved carapace, was collected from a thick-bedded spongiolithic limestone of the Upper Jurassic Treuchtlingen Formation (early late Kimmeridgian, Acanthicum Zone). Petersbuchia adds to the diversification hotspot of early true crabs within the sponge-microbial magnafacies along the northern shelve of the Tethys Ocean in general and to the brachyuran fauna of the Treuchtlingen Formation in special.

Devonian to Triassic tectonic evolution and basin transition in the East Kunlun−Qaidam area, northern Tibetan Plateau: Constraints from stratigraphy and detrital zircon U−Pb geochronology

The late Paleozoic to Triassic was an important interval for the East Kunlun−Qaidam area, northern Tibet, as it witnessed prolonged subduction of the South Kunlun Ocean, a major branch of the Paleo-Tethys Ocean whose closure led to the formation of Pangea. However, the geologic history of this stage is poorly constrained due to the paucity of tectonothermal signatures preserved during a magmatic lull. This article presents a set of new provenance data incorporating stratigraphic correlation, sandstone petrology, and zircon U−Pb dating to depict changes in provenance that record multiple stages of topographic and tectonic transition in the East Kunlun−Qaidam area over time in response to the evolution of the South Kunlun Ocean. Devonian intra-arc rifting is recorded by bimodal volcanism and rapid alluvial-lacustrine sedimentation in the North Qaidam Ultra High/High Pressure Belt, whose sources include the Olongbuluke Terrane and southern North Qaidam Ultra High/High Pressure Belt. Southward transgression submerged the East Kunlun−Qaidam area during the Carboniferous prior to the rapid uplift of the Kunlun arc, which changed the provenance during the Early Permian. This shift in provenance for the western Olongbuluke Terrane and thick carbonate deposition throughout the North Qaidam Ultra High/High Pressure Belt in the late Early Carboniferous indicate that the North Qaidam Ultra High/High Pressure Belt should have been inundated, terminating an ∼95 m.y. erosion history. The closure of the South Kunlun Ocean in the late Triassic generated a retroarc foreland along the Zongwulong Tectonic Belt, which is represented by the development of a deep-water, northward-tapering flysch deposystem that was supplied by the widely elevated Kunlun−Qaidam−Olongbuluke Terrane highland. This new scenario allows us to evaluate current models concerning the assembly of northern Tibet and the tectonic evolution of the Paleo-Tethys Ocean.

Origin of the Multiple-Sourced Cherts in Maokou Carbonates in Sichuan Basin, South China

Cherts have been thought to originate from biosilicification, terrestrial inputs and hydrothermal activity. The study of cherts is helpful in understanding the paleo-ocean environment and tectonic–sedimentary processes. Large amounts of cherts occur widely in the Maokou Formation in the Sichuan Basin, which may be largely connected to the Permian Chert Event (PCE). However, the source of silica and the formation process of cherts remain debated. Here, we analyze the petrographic and geochemical features of the cherts from the Guadalupian Maokou Formation (~268–259 Ma) in six sections in the Sichuan Basin. Two main types of cherts, nodular and bedded, are recognized in the Maokou Formation. The formation of nodular cherts was mainly affected by hydrothermal fluids, whereas the bedded cherts are mainly of biogenetic origin. The Emeishan large igneous province (ELIP) caused the activation of deep faults, accompanied by intense hydrothermal activities. Correspondingly, the cherts of significant hydrothermal origin developed near the active deep faults. The intensified hydrothermal activities may provide extra silica supplies and flourish the silica-secreting organisms by the associated volcanogenic upwellings that facilitated the enrichment of cherts. The study of Maokou cherts can help to record the volcanic- and silicon-related biological activities in the eastern Paleo-Tethys Ocean and can provide significant implications for chert enrichment in analogous settings.