Topic
Oldest dated rocks
About: Oldest dated rocks is a research topic. Over the lifetime, 4 publications have been published within this topic receiving 53 citations.
Papers
TL;DR: In this article, a detailed geochemical, isotopic, and geochronological study was carried out on felsic volcanic rocks from the southern part of the North Baikal volcanoplutonic belt.
Abstract: Detailed geochemical, isotopic, and geochronological studies were carried out on felsic volcanic rocks from the southern part of the North Baikal volcanoplutonic belt. U-Pb zircon dating showed that the rocks previously ascribed to a single stratigraphic unit (Khibelen Formation of the Akitkan Group or the Khibelen Complex) have significant age differences. The Khibelen Formation was found out to include both the oldest dated rocks (1877.7 ± 3.8 Ma) of the North Baikal belt and the younger volcanic rocks (1849 ± 11 Ma). Two other dated volcanic rocks have intermediate ages (1875 ± 14 and 1870.7 ± 4.2 Ma). It was established that the volcanic rocks from various areas in the southern part of the North Baikal belt not only have different ages but also differ in geochemical and isotopic signatures. In particular, the felsic volcanic rocks from various sites show the following variations in trace-element composition: from 220–280 to 650–717 ppm Zr, from 8–12 to 54–64 ppm Nb, and from 924–986 to 1576–2398 Ba. The ɛNd obtained for felsic volcanic rocks and comagmatic granitoids from various areas in the southern part of the North Baikal belt vary, respectively, from −1.7 to −2.8 and from −8.0 to −9.2. Based on geochemical and isotopic signatures, the felsic volcanic rocks in various areas of the southern part of the North Baikal volcanoplutonic belt were formed via the melting of a Mesoarchean crustal source of tonalite composition with contribution of variable amounts of juvenile mantle material at different magma generation conditions. Isotopic data indicate that the contribution of juvenile mantle material to their sources varied from ∼33–40 to 77–86%. The maximal calculated temperatures of the parent melts for felsic volcanic rocks were 908–951°C, and the lowest temperatures were 800–833°C. The geochemical signatures of dacites with an age of 1877.7 ± 3.8 Ma such as high Th (46–51 ppm) and La (148–178 ppm) contents indicate that these rocks, along with Mesoarchean granitoid and juvenile mantle material, contain an upper crustal component with high Th and LREE contents. Extremely low Y and Yb contents in these dacites implies their formation at pressures of ∼ 12–15 kbar in equilibrium with garnet-bearing residue. These rocks were presumably formed in the collisional-thickened crust at the earliest stages of its collapse, possibly during syncollisional collapse, with additional hear input to the lower crust. Other felsic rocks are geochemical analogues of A-type granites and were formed during the subsequent stages of collapse (post-collisional collapse).
35 citations
TL;DR: In this article, the authors reviewed the evolution of southwestern Sweden and provided a background for the dating of the Varberg charnockite, and showed that the alleged Gothian and western Pregothian regions pass continuously into each other.
Abstract: The Precambrian evolution of south-western Sweden is reviewed concisely to provide a background for the dating of the Varberg charnockite. It is shown that the alleged Gothian and western Pregothian regions pass continuously into each other. In the west, the oldest dated rocks have ages around 1700 Ma. An older (Svecokarelian?) basement may be present in the eastern parts of the region. Basic magmatism, metamorphism and the relationship between orogenic and anorogenic events are discussed.
18 citations
1 Jan 1976
TL;DR: The Vizcaino Peninsula, Baja California Sur, includes the largest continuous exposure of pre-Cenozoic rocks in the Continental Borderland of Peninsular California as mentioned in this paper.
Abstract: The rocks of the Vizcaino Peninsula, Baja California Sur, include the largest continuous exposure of pre-Cenozoic rocks in the Continental Borderland of Peninsular California. The oldest dated rocks are the upper Triassic volcanic-volcaniclastic sequence at Puerto San Hipolito. Several tectonic belts expose mafic-ultramafic rocks, apparently from the oceanic crust and at least Early Jurassic in age. In mid-Jurassic time the peninsula was intruded by tonalite plutons. These had been uplifted and erosionally exposed by Late Jurassic time, as tonalite debris appears locally in the Late Jurassic Eugenia Formation. In Early Cretaceous time the Eugenia Formation was extensively intruded by andesite porphyry dikes. The Eugenia, together with the dikes, is unconformably overlain by more than 10,000 metres of Valle Formation, largely sandstone and shale with major lenses of conglomerate in its middle portion. The Valle Formation varies in age from Upper Albian to very Late Cretaceous and is overlain comformably by earliest Paleocene. Diatomaceous and volcanic Miocene, arenaceous Pliocene, and thin, largely continental Pleistocene formations complete the stratigraphic sequence. Much of the faulting and folding in the Peninsula is of post-Miocene age.
13 citations
TL;DR: The recorded geological history of Malaya begins with a Cambrian to Silurian orthoquartz-ite-carbonate fades, largely predating geosynclinal conditions which were apparently initiated in the latter half of the Ordovician period as discussed by the authors.
Abstract: Malaya occupies two tectonic contexts. It constitutes part of an orogenic belt extending northward through west Thailand, east Burma, and southwest China and southward into Indonesia. This belt was cratonized by Late Triassic orogeny and plutonism so that, subsequently, Malaya formed part of the stable Sunda Shield. The recorded geological history of Malaya begins with a Cambrian to Silurian orthoquartz-ite-carbonate fades, largely predating geosynclinal conditions which were apparently initiated in the latter half of the Ordovician period. Throughout its existence the geosyncline comprised a eugeosynclinal zone located in the eastern and axial parts of the country and a miogeosynclinal zone situated in western Malaya. The earliest known component of the geosynclinal succession is an Ordovician to Lower Devonian euxinic facies in the miogeosyncline. This facies passes up into flysch of Middle Devonian to Early Carboniferous age. In the eugeosyncline, the oldest dated rocks are Lower Devonian shales, chert...
5 citations
Performance Metrics
| Year | Papers |
|---|---|
| 2008 | 1 |
| 1980 | 1 |
| 1976 | 1 |
| 1972 | 1 |