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Tectonic Blocks (tectonic + block)
Selected AbstractsThe Ohalo II prehistoric camp (19.5 Ky): New evidence for environmental and tectonic changes at the Sea of GalileeGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2002Shmuel Belitzky Combined archaeological data, shore surveys, and aerial photos of submerged sediments in the Sea of Galilee provide new insights into environmental and tectonic events, their dating, and their impact on the Ohalo II prehistoric camp (ca. 19,500 yr B.P.) and its surroundings. The Ohalo II waterlogged campsite contains excellently preserved brush hut remains and other in situ features, all embedded in late Pleistocene lacustrine strata. The findings indicate relatively short occupation of the site, not more than months or several years at a time. The high quality in situ preservation of delicate organic materials, as well as the short occupation period, suggests a quick and gentle burial by fine sediments. The evident fast submergence (water level rise of the Sea of Galilee) could have been the result of climatic fluctuations towards the end of the last glaciation and/or small-scale tectonic subsidence. The site is located on a tectonic block formed in the western fault belt of the Dead Sea Rift. We present new evidence of post-occupational folding of the late Pleistocene strata and recent tilting and faulting. A westward tectonic tilt may have caused the blockage of the old Jordan River outlet after A. D. 1106. Excellent preservation of the fault traces to the east of the site is attributed to the young age of the displacement on the fault. The last displacement apparently post-dates the blockage of the old Jordan River. © 2002 Wiley Periodicals, Inc. [source] Amphibolite and blueschist,greenschist facies metamorphism, Blue Mountain inlier, eastern JamaicaGEOLOGICAL JOURNAL, Issue 5 2008Richard N. Abbott Jr Abstract Cretaceous (possibly older) metamorphic rock occurs mainly in the Blue Mountain inlier in eastern Jamaica. Fault-bounded blocks reveal two styles of metamorphism, Westphalia Schist (upper amphibolite facies) and Mt. Hibernia Schist (blueschist (BS),greenschist (GS) facies). Both Westphalia Schist and Mt. Hibernia Schist preserve detailed records of retrograde P,T paths. The paths are independent, but consistent with different parts of the type-Sanbagawa metamorphic facies series in Japan. For each path, phase relationships and estimated P,T conditions support a two-stage P,T history involving residence at depth, followed by rapid uplift and cooling. Conditions of residence vary depending on the level in a tectonic block. For the critical mineral reaction (isograd) in Westphalia Schist, conditions were P ,7.5,kbars, T ,600°C (upper amphibolite facies). Retrograde conditions in Hibernia Schist were P,=,2.6,3.0,kbars, T,=,219,237°C for a(H2O),=,0.8,1.0 (GS facies). Mt. Hibernia Schist may represent a volume of rock that was separated and uplifted at an early time from an otherwise protracted P,T path of the sort that produced the Westphalia Schist. Reset K,Ar ages for hornblende and biotite indicate only that retrograde metamorphism of Westphalia Schist took place prior to 76.5,Ma (pre-Campanian). Uplift may have commenced with an Albian,Aptian (,112,Ma) orogenic event. Copyright © 2008 John Wiley & Sons, Ltd. [source] Prograde eclogites from the Tonaru epidote amphibolite mass in the Sambagawa Metamorphic Belt, central Shikoku, southwest JapanISLAND ARC, Issue 3 2005Yasuo Miyagi Abstract Prograde eclogites occur in the Tonaru epidote amphibolite mass in the Sambagawa Metamorphic Belt of central Shikoku. The Tonaru mass is considered to be a metamorphosed layered gabbro, and occurs as a large tectonic block (approximately 6.5 km × 1 km) in a high-grade portion of the Sambagawa schists. The Tonaru mass experienced high- P/low- T prograde metamorphism from the epidote-blueschist facies to the eclogite facies prior to its emplacement into the Sambagawa schists. The estimated P,T conditions are T = 300,450°C and P = 0.7,1.1 GPa for the epidote-blueschist facies, and the peak P,T conditions for the eclogite facies are T = 700,730°C and P , 1.5 GPa. Following the eclogite facies metamorphism, the Tonaru mass was retrograded to the epidote amphibolite facies. It subsequently underwent additional prograde Sambagawa metamorphism, together with the surrounding Sambagawa schists, until the conditions of the oligoclase,biotite zone were reached. The high- P/low- T prograde metamorphism of the eclogite facies in the Tonaru mass and other tectonic blocks show similar steep dP/dT geothermal gradients despite their diverse peak P,T conditions, suggesting that these tectonic blocks reached different depths in the subduction zone. The individual rocks in each metamorphic zone of the Sambagawa schists also recorded steep dP/dT geothermal gradients during the early stages of the Sambagawa prograde metamorphism, and these gradients are similar to those of the eclogite-bearing tectonic blocks. Therefore, the eclogite-bearing tectonic blocks reached greater depths in the subduction zone than the Sambagawa schists. All the tectonic blocks were ultimately emplaced into the hanging wall side of the later-subducted Sambagawa high-grade schists during their exhumation. [source] From the intra-desert ridges to the marine carbonate island chain: middle to late Permian (Upper Rotliegend,Lower Zechstein) of the Wolsztyn,Pogorzela high, west PolandGEOLOGICAL JOURNAL, Issue 2-3 2010Hubert Kiersnowski Abstract The tectonic Wolsztyn,Pogorzela palaeo-High (WPH) is the south-eastern termination of the Brandenburg,Wolsztyn High (western Poland), which during Late Permian times was an intra-basin ridge surrounded by Upper Rotliegend sedimentary basins within the Southern Permian Basin. The geological history and structural framework of the WPH are complex. The High belongs to the Variscan Externides, consisting at present of strongly folded, faulted and eroded Viséan to Namurian flysch deposits capped by a thick cover of Upper Carboniferous,Lower Permian volcanic rocks. This sedimentary-volcanic complex was strongly fragmented and vertically differentiated by tectonic movements and subsequently eroded, resulting in the deposition of coarse clastics surrounding uplifted tectonic blocks. During late Rotliegend time, arid climatic conditions significantly influenced occurrences of specific facies assemblages: alluvial, fluvial, aeolian and playa. Sedimentological study helped to recognize the interplay of tectonic and palaeoclimatic factors and to understand the phenomenon of aeolian sandstones interbedded with coarse deposits of alluvial cones close to fault scarps. Subsequent tectonic and possible thermal subsidence of the studied area was synchronous with inundation by the Zechstein Sea. The rapid inundation process allowed for the preservation of an almost perfectly protected Uppermost Rotliegend landscape. Based on 3D seismic data from the base Zechstein reflector, a reconstruction of Rotliegend palaeogeomorphology was carried out, which shows examples of tectonic rejuvenation of particular tectonic blocks within the WPH area before inundation by the Zechstein Sea. The inundation led to the deposition of the marine Kupferschiefer Shale followed by the Zechstein Limestone. In the deeper parts of the basin the latter is developed in thin basinal facies: in shallow parts (e.g. uplifted tectonic blocks forming in some cases islands), carbonate buildups were formed. The remarkable thickness of those buildups (bryozoan reefs) is interpreted as due to stable tectonic subsidence together with a rise of sea level. A detailed study of carbonate buildups has showed that their internal structure reflects changes in shallow marine environments and even emersion events, caused by sea-level oscillations and tectonic movements of the reef substrate. Copyright © 2010 John Wiley & Sons, Ltd. [source] Regional GPS data confirm high strain accumulation prior to the 2000 June 4 Mw= 7.8 earthquake at southeast SumatraGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001G. W. Michel Summary Site velocities derived from repeated measurements in a regional GPS network in Southeast Asia help to constrain the motion of tectonic blocks as well as slip rates along major faults in the area. Using 3-D forward dislocation modelling, the influence of seismic elastic loading and unloading on the measured site motions are approximated. Results suggest that the northwestern Sunda arc is fully coupled seismogenically, whereas its eastern part along Java shows localized deformation. Higher horizontal velocity gradients than expected from the modelling of a fully coupled plate interface west of Manila in the Philippines suggest that deformation may be localized there. Assuming that geodetically derived convergence represents long-term rates, accumulated geodetic moments are compared to those derived using seismic data from 1977 to 2000 (Harvard CMT catalogue). If areas displaying localized deformation are dominated by creep processes, the largest difference between accumulated and seismically released deformation is located where the 2000 June 4 Mw = 7.8 Sumatra earthquake occurred. [source] Prograde eclogites from the Tonaru epidote amphibolite mass in the Sambagawa Metamorphic Belt, central Shikoku, southwest JapanISLAND ARC, Issue 3 2005Yasuo Miyagi Abstract Prograde eclogites occur in the Tonaru epidote amphibolite mass in the Sambagawa Metamorphic Belt of central Shikoku. The Tonaru mass is considered to be a metamorphosed layered gabbro, and occurs as a large tectonic block (approximately 6.5 km × 1 km) in a high-grade portion of the Sambagawa schists. The Tonaru mass experienced high- P/low- T prograde metamorphism from the epidote-blueschist facies to the eclogite facies prior to its emplacement into the Sambagawa schists. The estimated P,T conditions are T = 300,450°C and P = 0.7,1.1 GPa for the epidote-blueschist facies, and the peak P,T conditions for the eclogite facies are T = 700,730°C and P , 1.5 GPa. Following the eclogite facies metamorphism, the Tonaru mass was retrograded to the epidote amphibolite facies. It subsequently underwent additional prograde Sambagawa metamorphism, together with the surrounding Sambagawa schists, until the conditions of the oligoclase,biotite zone were reached. The high- P/low- T prograde metamorphism of the eclogite facies in the Tonaru mass and other tectonic blocks show similar steep dP/dT geothermal gradients despite their diverse peak P,T conditions, suggesting that these tectonic blocks reached different depths in the subduction zone. The individual rocks in each metamorphic zone of the Sambagawa schists also recorded steep dP/dT geothermal gradients during the early stages of the Sambagawa prograde metamorphism, and these gradients are similar to those of the eclogite-bearing tectonic blocks. Therefore, the eclogite-bearing tectonic blocks reached greater depths in the subduction zone than the Sambagawa schists. All the tectonic blocks were ultimately emplaced into the hanging wall side of the later-subducted Sambagawa high-grade schists during their exhumation. [source] Structural position of the Seba eclogite unit in the Sambagawa Belt: Supporting evidence for an eclogite nappeISLAND ARC, Issue 2 2002Article first published online: 4 JUL 200, Mutsuki Aoya Abstract Eclogite-bearing units in the Sambagawa Metamorphic Belt have long been considered tectonic blocks that have disparate tectonic and metamorphic histories that are distinct from each other and from the major non-eclogitic Sambagawa schists. However, recent studies have shown that eclogite facies metamorphism of the Seba eclogite unit is related to the subduction event that caused the metamorphism of the non-eclogitic Sambagawa schist. New structural data further show that the Seba eclogite unit, which appears to be isolated from the other eclogite units, is in fact in structural continuity with them, occupying the highest structural levels in the Sambagawa Belt. This suggests that eclogitic metamorphism of the other eclogite units is also related to the Sambagawa subduction event. It is, therefore, possible that all eclogite units in the Sambagawa Belt constitute a single coherent unit, the eclogite nappe, members of which underwent the same eclogitic metamorphism related to the Sambagawa subduction event. [source] | ||||||||||