During the late Permian in Mongolia, inertia-driven transtensive reactivation of primordial fracture zones gave rise to the development of a sequence of related, but isolated, fault-bounded ...sub-basins; some of these became the locus of substantial peat accumulation that evolved into economically important coal deposits. The present study focuses on late Permian coal measures in two widely separated areas: Area 1: located in central Mongolia, developed along the southern margin of the Mongol-Transbaikalian Seaway. The late Permian coal sequence forms a c. 420 m thick middle part of a Permo-Triassic succession which spans c. 2,600 m. The V-shaped, fault-bounded NE oriented sub-basin evolved under transtensive conditions. The thick infill records a transition from shallow marine and humid coal forming depositional environments during the late Permian to relatively arid desolate terrestrial conditions during early Triassic times, considered here to mark the dramatic drainage of the Mongol-Transbaikalian Seaway across the Permo-Triassic boundary. Area 2: situated in southern Mongolia, is a NE oriented elongate sub-basin, bounded by two wrench faults, which formed under transtensive conditions. Thickness of the late Permian coal-bearing strata is c. 650 m. The sedimentary strata record a transition from a humid coal-bearing environment to predominantly marine conditions. Both study areas are located proximal to two controversial suture zones. However, the zones do not show the presumed shortening, major thrusting, regional metamorphism and given the complete absence of tuffs within the studied Permo-Triassic successions it could be argued that the sutures are not only cryptic but non-existent.
Mongolia is exceptionally rich in coal and copper-gold resources - with world-class deposits like Tavan Tolgoi, Oyu Tolgoi and Erdenet. Thus, the mining industry has a crucial importance for the ...national economy, yet most of the country remain very underexplored. Within today's global tectonics, an acceptable understanding of metal enrichments - including leaching, the internal hydrostatic-hydraulic pumping system, and surface emplacement mechanisms - has remained unresolved. However, a broader view of the structural situation in the Mongolia-China region shows a close link between orientation of elongate sedimentary basins, important mineral belts, and the fundamental orthogonal fracture/fault system. In the east the tectonic trend is dominantly northeast, while it is northwest in western areas. The main east Mongolian graphite deposits have northeast structural trends like numerous regional Cu and Au belts. A new theory of the earth, Global Wrench Tectonics, offers an exciting approach to better understanding the various facets of Earth's geological history and its surface resources. Earth’s degassing, dynamo-tectonic consequences, inertia-driven crustal wrench tectonics, as well as surface products such as water, hydrocarbons and ore deposits are given a coherent system explanation. Many hydrocarbons are products from the interior of our slowly degassing Earth, with massive hydrocarbon fields such as Songliao and the Yamal megaproject producing from the basement. Crustal thinning in the Songliao region is about the same as in southeast Mongolia, suggesting that they may have had similar degassing and crustal evolution histories. As such, it is not unlikely that the underexplored Mesozoic basins of southeast Mongolia - particularly at the deepest levels and/or in the adjacent crystalline basement - may have important hydrocarbon potential.
A palaeomagnetic study of the 100 to 90 m.y. old alkaline igneous rocks of the French Pyrenees has in part revealed large between-site scatter caused by highly variable declination. ...Magnetomineralogical evidence suggests that the original titano-magnetite has undergone variable low-temperature oxidation through martitization and maghemitization processes, suggesting that the rocks have been remagnetized. When viewed in the context of the Upper Cretaceous-Lower Tertiary inclination pattern based on Portuguese palaeomagnetic data, it is concluded that the rocks most likely acquired their present magnetization during early Campanian-Maastrichtian time, i.e. 20-30 m.y. after their original cooling. On the other hand, this magnetization postdates a major phase of late Cretaceous compressive deformation. Subsequent strike-slip movement along the Pyrenean zone in the Lower Tertiary led to variable rotation of cover units along the orogenic belt, producing the inconsistent palaeomagnetic declination picture presently observed. It is concluded that the geological history of the alkaline rocks of the French Pyrenees, from the magmatic stage to the subsequent events of remagnetization and tectonic deformation, is strongly associated with the Alpine-age rotational instability of Iberia. The principal kinematic history of the Peninsula comprised ca. 40° counterclockwise rotation (relative to Europe) during Cenomanian- Turonian time (100-90 m.y. ago) followed by ca. 70° clockwise rotation in the early Campanian (ca. 75 m.y. ago).PUBLICATION ABSTRACT
The Dingle Group, a continental Upper Silurian redbed succession in SW Ireland, has yielded a multicomponent palaeomagnetic record. The oldest magnetization retrieved, the B component, with in situ ...mean direction of D/I = 191/+9; K = 40; α95 = 3.6°; N = 41, post-dates the local late Silurian-mid-Devonian (Acadian) tectonic deformation and is in very good agreement with the prevailing remanences in other Caledonian rocks of western Ireland. An overprinted ‘A’ component with in situ mean direction D/I = 194/-16; K = 53; α95 = 3.1°; N = 41, is about as prevalent as the B component and was probably acquired in late Palaeozoic (Kiaman) times. By comparison with other published data, including a positive fold test for corresponding magnetization of Upper Silurian redbeds in Clare Island, it is concluded that the flat-lying B field (relative to Britain and Ireland) was in existence at least from the late Silurian to late Middle Carboniferous, i.e. covering a minimum time span of 100 M. yr.
The Foyers Sandstone, a constituent of the Old Red Sandstone of northern Scotland, located on the eastern flank of the Great Glen Fault, has yielded a multicomponent palaeomagnetic structure. The ...principal magnetization (called the B component), with in situ mean direction D, I = 185°, +8°; α95 = 2.7°, post-dates the local ‘mid’-Devonian (Acadian) tectonic event, but this direction corresponds well with characteristic directions displayed by Devonian and Lower Carboniferous rocks of Scotland. The most significant overprinted component, the A2 magnetization, with in situ mean direction D, I = 194°, -27°; α95 = 4.1°, has a more patchy occurrence than the B remanence, the strongest development of A2 being observed at sites that are situated close to the Great Glen Fault zone. The A2 direction is consistent with a Hercynian age. A third magnetization, the Al component, of suggested Lower Tertiary age, has been found at one of the sites close to the fault zone. The A2 and B remanences support previously proposed declination discordances in corresponding magnetizations across the Great Glen Fault. It is concluded that the Foyers Sandstone developed its multicomponent magnetization through repeated tectonic events on the Great Glen Fault in Acadian, Hercynian and Alpine times respectively.
Results of palaeomagnetic and rock magnetic studies are reported mainly for quartz porphyry collected at 18 sites from an Ordovician igneous-sedimentary succession at Tourmakeady and Glensaul in Co. ...Mayo, Eire. Both magnetite and haematite are shown to be prominent magnetic constituents. The magnetite is usually in the form of large multidomain grains; these are held responsible for a soft remanence component (called the B-magnetization) with D, I= 000, +75; α95= 3.7°, i.e. practically identical to the direction of the present axial geocentric dipole field in the area. Hence, it is inferred that the B-magnetization, which is dominant at most sites, is of recent origin. Haematite, which has a more patchy occurrence, apparently formed through high-temperature oxidation of magnetite. Haematite is the main carrier of the palaeomagnetically significant component, the A-magnetization, which gave well-grouped in situ directions (29 samples from 10 sites) with a mean value of D, I= 182°, +6°, corresponding to a north pole at 31° N, 169° E; dp, dm = 2.1°, 4.2°. Correction for folding along the Glensaul-Tourmakeady arc shows that the A-magnetization is of post-folding age. An earlier suggestion that the rocks represent a Lower Ordovician extrusive suite is discussed and discounted. It is inferred that the quartz porphyries constitute syntectonic intrusions having formed during the Taconic orogeny. These rocks as well as their characteristic magnetization are therefore regarded as late Ordovician in age. It is concluded that a c. 50° relative clockwise shift between the mid-Ordovician and late Ordovician-Silurian geomagnetic field axes, previously demonstrated for Scotland, has now been recognized also in Ireland.
We appreciate this opportunity to clarify our position on a few central issues of this debate. By our rejection of a number of Palaeozoic palaeomagnetic data from Scotland (Storetvedt et al. 1990), ...Torsvik et al. accuse us of disregarding all classical field tests. We have never disregarded any classical field test, but would argue that such tests have sometimes been misapplied. Also, we obviously have not rejected all earlier British ‘Siluro‐Devonian’data, including Scottish results (e.g. table 3, Storetvedt et al. 1990).
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