GP43C-01 INVITED 13:40h
The Contributions of Leonid M. Parfenov to the Tectonics of Eastern Russia
Leonid M. Parfenov (1937-2002) was the leading force behind theinterpretation of northeast Russia in the context of plate tectonics. Originally interested in Precambrian geology, he conducted his early field work in southern Siberia in the 1960s. He was exposed to plate tectonics at Liverpool University in 1970 and published the first mobilistic reconstructions of the Precambrian in Russia in 1973. Starting in 1971, he began to systematically conduct field work and accumulate geologic data on what is now considered the accretionary collage of northeast Russia. With colleague Boris A. Natal'in, he published a series of papers on the tectonic evolution of eastern Russia starting in 1977, with a doctoral dissertation on "Comparative Tectonics and Evolution History of Mesozoides of Northeast Asia" in 1983. His work became known in the west with his publication in 1978 in the Journal of Physics of the Earth on "Geodynamics of the North-Eastern Asia in the Mesozoic and Cenozoic Time and the Nature of Volcanic Belt" in which the volcanic belts of eastern Russia were interpreted in the context of subduction zones. From the mid-1980s to his death, he concentrated on understanding the evolution of the fold belts of eastern Yakutia. Parfenov immediately became a proponent of terrane analysis as it evolved in the early 1980s and was the primary mover in developing the terrane map of northeast Russia in the late 1990s. In 1990, he developed joint programs with the University of Alaska Fairbanks and Michigan State University, and later with Stanford University and the U.S. Geological Survey, opening eastern Russia to western scientists. His life's work was synthesized in a monograph entitled "Tectonics, Geodynamics, and metallogenesis of the Territory of the Sakha Republic (Yakutia)" published in Russian in 2001 and currently being prepared in English translation. As a result of his efforts we now have a basic understanding of the plate tectonic evolution of northeast Russia as a region of Phanerozoic rifting, terrane development, and collision.
GP43C-02 13:55h
Tectonics of NE Russia: Pivotal issues and uncertainties
The main feature of the tectonic setup of NE Russia is the existence there of two contrasting tectonic grains: (1) Verkhoyansk-Chukotka orogenic belt (VCOB) with a markedly mosaic tectonic style and predominance of NW trends modified by the "Kolyma loop," and (2) Koryak-Kamchatka orogenic belt (KKOB), with its typical NE-trending linear features, conformable to the general tectonic grain of the Circum-Pacific foldbelts. Such sharp contrast in the tectonic grain can be explained as follows: (i) evolution of the VCOB was dominated by collisional processes, whereas, the KKOA provided the stage for accretionary ones; (ii) the VCOB incorporates terranes with continental crust (microcontinents); (iii) the paleostructures of the VCOB were separated from the Pacific by a convergent boundary, and their origin was not therefore related to the motions of Pacific plates-as was the case with the terranes of the KKOA. The time of inception of the convergent boundary between Eurasia and NW Pacific remains poorly constrained. Reliable reconstructions become feasible starting only from as late as the Late Jurassic. There are two different approaches on the origin and evolution of South Anyui suture (SAS): (1) Late Mesozoic rift; and (2) remnant after the closure of a Pacific re-entrant. The multiplicity of the viewpoints is due to the insufficient knowledge of the region and, primarily, to the lack of reliable data on (i) the structures of the different segments of the SAS and its northern and southern surroundings; (ii) age of the oceanic fragments; (iii) the tectonic position and geodynamic settings of the ophiolites; (iv) timing of the principal geologic events such as metamorphism, island-arc volcanism, granite emplacement, collision, etc.; (v) depositional environments and clastic sources of the Triassic -Early Cretaceous sediments. These white spots in our knowledge of the tectonic setup of the Chukotka Peninsula prevent us from adopting or rejecting the popular tectonic model viewing Chukotka as a microplate that split off Canada's Arctic margin to eventually dock onto the North Asian continent. In the KKOA, the pivotal issue is the original location of terranes, their travel paths, and the timing and mode of their accretion. This applies to the following terranes: (i) Ganychalan, including Early Paleozoic ophiolites that have no counterparts anywhere in NE Asia and that are likely fragments of oceanic lithosphere of the Pacific, Iapetus, or the Paleo-Asian Ocean; and (ii) the terranes carrying Late Paleozoic limestones and Tethyan faunas. Such units are common within the northern Circum-Pacific accretionary complexes (Cache Creek terrane in British Columbia, Akieshi terrane in Japan, etc.), and they are critical to paleotectonic reconstructions; and (iii) the numerous and diverse island arc terranes with both Tethyan and boreal faunas. It should be investigated which island arc terranes provided convergent boundaries to which plates, and by which Pacific plates these terranes were transported. Supported by the Russian Foundation for Basic Research (project 02-05-64217).
GP43C-03 INVITED 14:10h
The Seismicity and Crustal Structure of Continental Eastern Russia
Regional networks were established under the Former Soviet Union to monitor seismic activity and evaluate seismic hazards. In eastern Russia, these networks were deployed starting in the early 1960s. The networks generally operated analog short-period instruments, with some base stations having long-period sensors. Approximately 50,000 events have been located on the continental part of eastern Russia. These earthquakes define the boundaries between three major (Pacific, North America, Eurasia), and several minor (Bering, Okhotsk, Amur, Primoria) plates. The zones of seismic activity are diffuse and indicate that deformation between these plates is distributed over a large number of faults. Major strike-slip faults can be identified both by linear trends in the larger seismicity and in satellite imagery; examples include the Ulakhan fault system, between North America and Okhotsk, the Ketanda fault system between Okhotsk and Eurasia, and a system of faults in southern Yakutia and the Stanovoi Range between Eurasia and Amur. Regional arrivals at Russian seismic stations were used to determine crustal P- and S-wave velocities. A grid search method conducted along a moving window through eastern Russia to find best-fit velocities for minimizing travel-time residuals yields a model that is consistent with the tectonic setting (cratons, rift zones). Preliminary ground-truth experiments in the Magadan district show a good fit between the determined best-fit velocities and those from industrial explosions, as do those from previous Russian seismic surveys. Earthquake relocations using these best-fit velocities, and combining data from between networks, reveal linear trends and clusters which can be associated with active faults. Considerable contamination of the Russian seismicity catalog by industrial explosions has also occurred.
GP43C-04 14:25h
Phanerozoic Tectonic Evolution of the Chukotka-Arctic Alaska Block: Problems of the Rotational Model
Correlation of tectonostratigraphic units across the Bering Strait suggests that the northern Chukotka including most of the East Siberian Shelf as well as the Brooks Range, Colville Basin, Beaufort Shelf, and Seward Peninsula on the North American side represent a large continental block. The core of this block consists of the Neoproterozoic Bennett-Barrovia block (BBB) that is overlain by the Ordovician-Devonian Novosibirsk carbonate platform. The basement of the block is exposed in the Chukotka Peninsula where orthogneiss yielded Late Proterozoic (650 to 550 Ma) U-Pb ages. These dates are comparable with the age of 699 Ma reported for granites in the Wrangel island. Granites of the same age intrude metasedimentary and metavolcanic rocks in the Hammond subterrane in northern Alaska. In the western part of the BBB, geophysical data imply a presence of a crystalline Precambrian basement at shallow depth beneath the Novosibirsk Archipelago. Weak deformation and consistency of facies of Ordovician-Devonian shelf and lagoon carbonates indicate that the BBB evolved as a rigid structure. A similarity of the Ordovician fossils with Siberia allows an inference about a close location of these two continental entities. The BBB forms a backbone of the Chukotka-Alaska block. Since the early Paleozoic, it started to grow at the expense of subduction-accretion. Ordovician and Silurian oceanic and island arc rocks mark the northern boundary of the BBB. This subduction boundary stopped its development after the late Silurian-early Devonian collision of the BBB and the North America craton. Subduction along the southern boundary of the BBB is recorded by a Devonian-early Carboniferous magmatic arc (granites yielding 360-398 Ma) and an extensional (backarc) basin. Perhaps, this subduction was terminated by a middle Carboniferous collision. The Triassic extension along the same boundary caused formation of the South Anyui ocean and a wide passive continental margin exposed in the northern Chukotka. The early Cretaceous closure of the ocean was followed by longitudinal shortening of the Chukotka-Arctic Alaska block as it is evident from orogen-parallel strike-slip faults and oroclinal bending of structural trends. The Bering Sea orocline accounts for almost double shortening of the original length of the Chukotka-Arctic Alaska block between the Chukotka and Seaward peninsulas. This shortening caused thickening of the crust and its extensional collapse that led to exhumation of metamorphic complexes. The reviewed tectonic structure and history impose constrains on geometry of the Chukotka-Arctic Alaska block. In many tectonic models, its counterclockwise rotation because of the opening of the Canada Basin and the following collision with the mainland of Asia is considered as the primary mechanism of the Cretaceous orogeny. However, the present day length of the BBB stretching from the Alaska-Canada border in the east to the Novosibirsk Archipelago in the west contradicts to this simple scenario. The original length of the BBB must be longer if the Cretaceous longitudinal shortening is restored. To overcome the space problem it is suggested that in the late Mesozoic the BBB moved right laterally along the North American margin and that the opening of the Canada Basin is a consequence of this giant strike-slip motion.
GP43C-05 14:40h
Paleomagnetic Paleolatitudes for Northeast Russia: an Update
It is now generally accepted that Northeast Russia east of the Verkhoyansk fold and thrust belt is made up of multiple tectonic terranes. It also seems that these terranes can be divided into three main groups, the Kolyma-Omolon Superterrane (KOS) in the interior, the western extension of the Chukotka-Alaska Superterrane to the north and the "outboard" terranes to the south and east. The outboard terranes are separated from the other terrane groups by the Late Cretaceous Okhotsk-Chukotka volcanic belt. To date there are no reliable paleomagnetic data from within the Chukotka part of the northern superterrane, so reconstructions are based on models of the opening of the Arctic Ocean. The latest compilation of paleomagnetic data show large but systematic changes in paleolatitude with time for both the KOS and the outboard terranes. For the KOS, comparisons of the paleolatitudes with those for the Siberian craton shows that they could have been in their current relative positions in Devonian time, been displaced by as much as 40o southward by Permo-Triassic time, then moved rapidly northward during the Jurassic to regain their original relative latitude with respect to the craton. The record for the outboard terranes is much shorter, but supports the idea that they were carried by the plates of the Pacific and collided with the KOS in Cretaceous and later times. The paleomagnetic data from both the KOS and the outboard terranes hint at the possibility that there was a small southward paleolatitude change in Late Cretaceous-Early Tertiary time, perhaps indicating that the South Anuyi Ocean, which separated Chukotka from the KOS, closed before the Arctic ocean had finished opening.
GP43C-06 14:55h
Comparison of Stratigraphic and Structural Evolution of Verkhoyansk and Cordillera Miogeoclines
Many Precambrian plate restorations place one of the rifted margins of the Siberian craton against one of the rifted margins of Laurentia. Inherent in the proposed restorations is the implication that the conjugate margins share a similar geodynamic history of rifting and thermal subsidence until interrupted by other tectonic processes. We compare the stratigraphic and structural history of Verkhoyansk miogeocline of the rifted southeastern margin of the Siberian craton with that of the Cordilleran miogeocline of the rifted southwestern margin of the North American craton to test predictions of the Precambrian plate restoration of Sears and Price (2003). We report on the results of joint expeditions down the Belaya River of Siberia and to the Death Valley and White-Inyo region of southeastern California. We find many points of lithostratigraphic and structural similarity between correlative platformal and miogeoclinal units ranging in age from Mesoproterozoic to Carboniferous. Collections of clastic rocks from both regions are being processed for detrital zircon analysis to verify putative lithostratigraphic matches. Our preliminary observations are consistent with the proposaal of Sears and Price (2003) that the margins rifted apart during latest Precambrian and thermally subsided as passive conjugate margins during early Paleozoic. Both margins experienced significant tectonic interruptions during late Devonian to Carboniferous time.
GP43C-07 15:10h
Siberian Arctic Continental Margin: Constraints and Uncertainties of Plate Tectonic Models
Siberian Arctic Continental Margin (SACM) reveals a complicated tectonic history resulted from three major events: (1) Mesozoic collisions of various allochtonous blocks with Paleo-Siberian continental margin, (2) Opening of Canada Basin, and (3) Opening of Eurasia Basin. Despite considerable progress was achieved in the past 15 years owing to CDP seismic reflection surveys and satellite observations, some major points of SACM's structure and history are still poorly understood. According to the most accepted model, opening of the Canada Basin led to separation and counterclockwise rotation of North Alaskan-Chukchi Microplate until it collided with Siberian/Omolon margin along South Anyui Suture. However, the time and geometry of the opening are not properly constrained yet. Uniform rotation of North Alaskan-Chukchi Microplate by 66 deg. causes a significant overlap in the East Siberian Sea that cannot be explained by later extension of the SACM. Accepted age of the basin opening is 130-80 Ma, however, geological data show that South Anyui Suture was already completely closed by Aptian. In contrast, Cretaceous flood basalts suggest even later opening of the Canada Basin, which may have begun around 125 Ma. Chukchi Borderland, when remained at its present position, prevents closure of the Amerasia Basin. We suggest it was conjugated to what now the northeastern margin of East Siberian Sea is. Then it was detached from the SACM and moved to the present-day position during spreading episodes within the Arctic basins. However, the time of this event is unconstrained yet. Late Cretaceous-Cenozoic extension of the SACM was related to opening of the Eurasia Basin, and, probably, North Atlantic and Labrador Sea. It led to significant modification of SACM's initial architecture and created several profound rift systems. Extension of northern Laptev Shelf totals at least 190 km, which is about 47 % of the total divergence within adjacent Eurasia Basin. The northern East Siberian and Chukchi seas and Chukchi Borderland are the best candidates to account for some 200 km of the "missing extension". Using all available data we have revised structure and geological history of the SACM and speculated its relationships to the Canadian Arctic Margin in a "pre-Canada Basin" Arctic.
GP43C-08 15:25h
How Many and What Kinds of Plate Boundaries? Neotectonics North of the Active Arc, Kamchatka, Russian Far East
The Ozernoi Peninsula on Kamchatka exhibits neotectonic evidence comparable to many subduction zones, although this peninsula is north of the Kuril-Kamchatka subduction zone as identified by active volcanism and intense seismicity. This evidence includes active thrust faulting (Ozernoi tsunamigenic earthquake of 1969), Holocene marine terraces (uplift rates of ca. 1 mm/yr), tsunami history (recurrence of tsunamigenic earthquakes about 200 yr), uplifted Quaternary marine terraces (uplift rates of at least 0.1 - 0.3 mm/yr), and Quaternary arc volcanism (albeit of an unusual chemistry). Karaginsky Island shares some of these same characteristics, though its neotectonics is not yet investigated in detail. We have also calculated convergence rates of about 15 mm/yr for the Ozernoi-Komandorskiy Basin juncture based on a fault-plane solution consistent with tsunamigenesis for the 1969 Ozernoi earthquake, extrapolated back for 2000 years, based on tsunami recurrence. Such a result, coupled with patterns of historic seismicity and Quaternary and Holocene marine terraces, suggests that Kamchatka may belong to an Okhotsk plate, perhaps as far north as Karaginsky Island, interacting with a Bering plate.