БАЙКАЛЬСКИЙ РИФТ: ПЛИОЦЕН (МИОЦЕН) – ЧЕТВЕРТИЧНЫЙ ЭПИЗОД ИЛИ ПРОДУКТ ДЛИТЕЛЬНОГО РАЗВИТИЯ С ПОЗДНЕГО МЕЛА ПОД ВОЗДЕЙСТВИЕМ РАЗЛИЧНЫХ ТЕКТОНИЧЕСКИХ ФАКТОРОВ. ОБЗОР ПРЕДСТАВЛЕНИЙ

The article reviews three typical concepts concerning the age of the Baikal rift (BR) which development is still underway: 5 Ma (the BR development start in the Late Pliocene), 30 Ma (Miocene or Oligocene), and 60–70 Ma (the Late Cretaceous). Under the concept of the young BR age (Pliocene–Quaternary) [Artyushkov, 1993; Nikolaev et al., 1985; Buslov, 2012], according to E.V. Artyushkov, BR is not a rift, but a graben due to the fact that the pre‐Pliocene structure of BR does not contain any elements that would be indicative of tensile stresses. However, field studies reported in [Lamakin, 1968; Ufimtsev, 1993; Zonenshain et al., 1995; Mats, 1993, 2012; Mats et al., 2001] have revealed that extension structures, such as tilted blocks and listric faults, are abundant in the Baikal basin (BB), and thus do not supportE.V. Artyushkov’s argumentation. The opinion that BR is young is shared by M.M. Buslov [2012]; he refers to studies of  Central Asia and states that only the Pliocene‐Quaternary structure of BB is a rift, while the oldest Cenozoic structures (Upper Cretaceous – Miocene) are just fragments of the large Cenozoic Predbaikalsky submontane trough (PBT) which are not related to the rift. However, the coeval Cenozoic lithological compositions, thicknesses of sediment layers and types of tectonic structures in PBT and BB have nothing in common. Across the area separating PBT and BB, there are no sediments or structures to justify a concept that BR and PBT may be viewed as composing a single region with uniform structures and formations. The idea of the Pliocene‐Quaternary age of BR should be rejected as it contradicts with the latest geological and geophysical data. Seismic profiling in BB has revealed the syn‐rift sedimentary bed which thickness exceeds 7.5 km. Results of drilling through the 600‐metre sedimentary sequence of Lake Baikal suggest the age of 8.4 Ma [Horiuchi et al., 2004], but M.M. Buslov believes that it took only about 5 Ma to form the entire syn‐rift sequence ofLake Baikal. In [Bazarov, 1986; Rasskazov et al., 2014; Mashchuk, Akulov, 2012; Hutchinson et al., 1993; Zonenshain et al., 1995; Kaz’min et al., 1995], the BR age is determined as the Miocene (Oligocene‐Miocene) according to the age of the Tankhoisuite (Miocene or Oligocene‐Miocene) and the correlation between the lower seismostratigraphic complex (SSC‐1) and the Tankhoi suite [Hutchinson et al., 1993; Zonenshain et al., 1995]. The Tankhoi suite lies directly on the crystalline basement of the rift and is believed to mark the start of the Baikal syn‐rift profile. However, this concept does not take into account the main specific feature of the profile, i.e. a developing rift. As shown in Fig. 6, the most ancient elements in the syn‐rift profile are inside the deep part of the rift. At the day surface, the basement is overlaid by the younger elements of the sedimentary wedge due to the ‘expansion non‐conformity effect’ (as termed in [Khain, Mikhailov, 1985]). In our opinion, it is incorrect to correlate SSC‐1 and the Tankhoi suires – the representative seismic profile (Fig. 5) shows that SSC‐1 falls out of the profile before reaching the day surface and leans against the rising slope of the basement, while SSC‐2 correlates with the Tankhoi suite. Besides, correlating SSC‐1 with the Tankhoi suite is contradicting to the data of structural studies reported in [San’kov et al., 1997; Delvaux et al., 1997]. SSC‐1 originated before the time when the Lake Baikal region was impacted by the Indo‐Eurasian collision and formed under the influence of pure expansion when tensile stresses were oriented from NW to SE across the strike of the rift along the SE 145–150° azimuth [Zonenshain et al., 1995]. By the time of the SSC‐2 formation, the stress vector turned counterclockwise towards the NE‐SW direction at an acute angle to the rift strike. The Baikal rift structure was changed as the single‐sided basin was replaced by the SW‐NE stretching dual‐sided graben; it included SSC‐2 and was bordered by listric faults [Zonenshain et al., 1995]. Results of the structural studies conducted on the Lake Baikal shores [San’kov et al., 1997; Delvaux et al., 1997; Parfeevets, San’kov, 2006] suggest that during the Tankhoi period, the rift developed in conditions of transpression and transtension under the influence of stresses oriented subparallel to the strike of the rift and related to the Indo‐ Eurasian collision. This means that SSC‐2 (but not SSC‐1) correlates with the Tankhoi suite, and the age of the Tankhoi suite is not indicative of the BR age, and the concept of the Miocene (Oligocene‐Miocene) age of BR is thus discarded. The concept of the Late Cretaceous‐Paleogenic age of BR [Logachev, 1974, 2003; Mats, 1987, 1993, 2012; Mats et al., 2001; Mats, Perepelova, 2011] is most fully supported by the available geological and geophysical data. This age is evidenced by the Paleogenic (Eocene) palinspectra detected in core samples from deep wells drilled in the Selenga river delta, Southern Baikal basin [Faizulina, Kozlova, 1966]. Besides, the Paleocene‐Eocene pre‐Tankhoi sediments are discovered at the Khamar‐Daban shore of the Southern Baikal basin (the Polovinka river valley) [Mats, 2013]. The sediments of the BB weathering crust [Mats, 2013] correlate with the paleontologically dated Paleogenic sediments of PBT [Pavlov et al., 1976; Popova, 1981]. The BR ancient age is also confirmed by studies reported in [Nikolaev, 1989; Galazii et al., 1999; Kontorovich et al., 2007; Jolivet et al., 2009]. Our review of the BR age concepts gives grounds to conclude that the Pliocene‐Quaternary and Oligocene‐Miocene (“Tankhoi”) ages of BR should be discarded as not supported by the geological and geophysical data collected in the recent studies. Based on the comprehensive studies of the Baikal rift and taking into account an extension of the BR evolution by 60 to 70 Ma, we propose a new concept of the BR development and introduce a three‐stage model (Fig. 7) (as a replacement of the well‐known two‐stage model [Logachev, 2003]) and an impactogenic model as a supplement to the passive and active rifting models [Mats, 2012; Mats, Perepelova, 2011]. In our model, the first stage of the BR development is the Late Cretaceous‐Early Oligocene (70–30 Ma): in conditions of the general extension of the lithosphere, BR forms as a slot‐type (the term proposed by E.E. Milanovsky) rift and develops, as shown by the passive rifting model, at the background of the original peneplain until the time when the Baikal region is impacted by stresses resulting from the Indo‐Eurasian collision; the rift structure is a single‐sided basin that comprises the seismically transparent seismostratigraphic complex (SSC‐1); it is bordered at NW by the zone of listric faults. The second stage is the Late Oligocene‐Early Pliocene (30–5 Ma): BR develops under the impact of stresses resulting from the Indo‐Eurasian collision; the dual‐sided graben is formed; it comprises SSC‐2 that is stratified and deformed. The third stage is the Late Pliocene – Quarter (5 Ma till present): BR develops under the impact of stresses generated by local deep sources, as shown by the active rifting model [Logachev, Zorin, 1987; Zorin et al., 2003]; another single‐sided graben is formed; it is bordered by listric faults from the NW and comprises SSC‐3 that is stratified but not deformed.Рассмотрены представления о возрасте Байкальского рифта (БР) и модели его развития. В литературе обсуждаются три варианта возраста БР – он формируется с позднего плиоцена (5 млн лет), с миоцена или олигоцена (30 млн лет), с позднего мела (60–70 млн лет). Его развитие продолжается в современную эпоху. Утверждения о молодом – плиоцен‐четвертичном – возрасте БР изложены в работах [Artyushkov, 1993; Nikolaev et al., 1985; Buslov, 2012; и др.]. Е.В. Артюшков считал, что в доплиоценовой Байкальской структуре отсутствуют элементы, свидетельствующие о напряжениях растяжения, и она не рифт, а грабен. Однако структуры растяжения (наклонные блоки, листрические разломы) широко распространены в Байкальской впадине (БВ) по всему ее разрезу [Lamakin, 1968; Ufimtsev, 1993; Zonenshain et al., 1995; Mats, 1993, 2012; Mats et al., 2001], и, таким образом, аргументация Е.В. Артюшкова оказалась несостоятельной. Оживил взгляды о молодом БР М.М. Буслов [Buslov, 2012], который, ссылаясь на исследования в Центральной Азии, считает рифтовой только плиоцен‐четвертичную структуру БВ. Древнейшие кайнозойские структуры (верхний мел – миоцен) являются, по М.М. Буслову, фрагментами крупного кайнозойского Предбайкальского предгорного прогиба (ППП) и не имеют отношения к рифту. Однако литолого‐формационный состав, мощность отложений и характер тектонических структур одновозрастных кайнозойских образований Предбайкальского прогиба и Байкальской впадины не имеют ничего общего. На разделяющих их пространствах отсутствуют какие‐либо отложения и структуры, которые позволили бы соединять в одну структурно‐формационную область БР и ППП. Все попытки соединить их в единое образование ничем не обоснованы, и утверждения о плиоцен-четвертичном возрасте БР должны быть отвергнуты как противоречащие новейшим геолого‐геофизическим данным и не учитывающие то, что сейсмическим профилированием в БВ установлена синрифтовая осадочная толща мощностью более 7.5 км. Этому также противоречит установленный бурением возраст в 8.4 млн лет 600‐метровой части разреза осадочной толщи Байкала [Horiuchi et al., 2004], тогда как по построениям М.М. Буслова на формирование всей синрифтовой толщи Байкала требуется всего лишь около 5 млн лет. Наиболее распространено мнение о миоценовом (олигоцен‐миоценовом) возрасте БР [Bazarov, 1986; Rasskazov et al., 2014; Mashchuk, Akulov, 2012; Hutchinson et al., 1993; Zonenshain et al., 1995; Kaz’min et al., 1995; и мн. др.]. Оно основано на признании танхойской свиты (миоцен или олигоцен‐миоцен) в качестве начинающей байкальский синрифтовый разрез, так как она залегает непосредственно на кристаллическом фундаменте рифта, а также на корреляции нижнего сейсмостратиграфического комплекса (ССК‐1) с танхойской свитой [Hutchinson et al., 1993; Zonenshain et al., 1995]. Но эти утверждения не учитывают основную закономерность строения разреза развивающегося рифта. Она заключается в том, что наиболее древние элементы синрифтового разреза скрыты в глубинной части рифта, а на дневной поверхности фундамент перекрывают более молодые элементы разреза (эффект несогласия растяжения [Khain, Mikhailov, 1985]). Корреляция ССК‐1 с танхойской свитой ошибочна – на представительном сейсмическом профиле видно (рис. 5), как ССК‐1, не доходя до дневной поверхности, выпадает из разреза, прислоняясь к подымающемуся склону фундамента, и с танхойской свитой коррелирует ССК‐2. Корреляции ССК‐1 с танхойской свитой противоречат также данные структурных исследований [San’kov et al., 1997; Delvaux et al., 1997]. ССК‐1 формировался до проникновения в Байкальский регион влияния Индо‐Евроазиатского столкновения, под воздействием чистого раздвига при ориентировке растягивающих напряжений с СЗ на ЮВ вкрест простирания рифта по азимуту ЮВ 145–150 [Zonenshain et al., 1995]. Ко времени формирования ССК‐2 вектор напряжений развернулся против часовой стрелки в направлении СВ‐ЮЗ под острым углом субпараллельно к простиранию рифта. Изменилась структура Байкальского рифта – одностороннюю впадину сменил двухсторонний грабен, простирающийся к ЮЗ‐СВ, выполненный ССК‐2 и ограниченный листрическими сбросами [Zonenshain et al., 1995]. Структурными исследованиями на суше, окружающей Байкал, установлено, что в танхойское время рифт развивался в обстановке транспрессии и транстензии, под воздействием напряжений, ориентированных субпараллельно простиранию рифта и связанных с Индо‐Евроазиатской коллизией [San’kov et al., 1997; Delvaux et al., 1997; Parfeevets, San'kov, 2006]. Таким образом, с танхойской свитой, по данным структурных исследований, коррелируется не ССК‐1, а ССК‐2, возраст танхойской свиты не является показателем возраста БР, и представление о его миоценовом (олигоцен‐миоценовом) возрасте должно быть отвергнуто. Наиболее полно имеющимся геолого‐геофизическим данным соответствует вывод о позднемеловом-палеогеновом возрасте БР [Logachev, 1974, 2003; Mats, 1987, 1993, 2012; Mats et al., 2001; Mats, Perepelova, 2011]. Это утверждение базируется на обнаружении в керне глубоких скважин, пробуренных в дельте р. Селенги (Южнобайкальская впадина), палеогеновых (эоцен) палиноспектров [Faizulina, Kozlova, 1966]. Кроме того, на хамар‐дабанском побережье Южного Байкала (р. Половинка) обнаружены палеоцен‐эоценовые дотанхойские отложения [Mats, 2013]. Отложения формации коры выветривания БВ коррелируются [Mats, 2013] с палеонтологически датированными палеогеновыми отложениями Предбайкальского прогиба [Pavlov et al., 1976; Popova, 1981]. Древний возраст БВ подтвержден также в работах [Nikolaev, 1998; Galazii et al., 1999; Kontorovich et al., 2007; Jolivet et al., 2009]. Обзор обсуждаемых представлений о возрасте БР приводит к заключению о необходимости исключить из рассмотрения заявления о его плиоцен‐четвертичном и олигоцен‐миоценовом («танхойском») возрасте как не отвечающие современным геолого‐геофизическим данным. Удлинение возраста БР до 60–70 млн лет и его комплексное изучение позволили сформулировать новый взгляд на Байкальский рифтогенез и предложить вместо известной двухэтапной модели его формирования [Logachev, 2003] трехэтапную (рис. 6), а также дополнить пассивную и активную модели рифтогенеза третьей – импактогенной [Mats, 2012; Mats, Perepelova, 2011]. На первом этапе – поздний мел – ранний олигоцен (70–30 млн лет) – БР формировался в условиях общего рассеянного растяжения литосферы в виде щелевого (по Е.Е. Милановскому) рифта, по пассивной модели, на фоне исходного пенеплена и до проникновения в Байкальский регион напряжений, продуцируемых Индо‐Евроазиатским столкновением. Структура рифта была образована в виде односторонней впадины, ограниченной с северо‐запада зоной листрических сбросов и выполненной сейсмически прозрачным сейсмострати-графическим комплексом – ССК‐1. На втором этапе – поздний олигоцен – ранний плиоцен (30–5 млн лет) – БР развивался под воздействием напряжений, продуцируемых Индо‐Евроазиатским столкновением. Был образован двухсторонний грабен, выполненный слоистым деформированным ССК‐2. На третьем этапе – поздний плиоцен – квартер (5 млн лет тому назад – современность) – рифт развивался под воздействием местных глубинных источников напряжений, по активной модели [Logachev, Zorin, 1987; Zorin et al., 2003]. Вновь сформировался односторонний грабен, ограниченный с северо‐запада листрическими разломами, выполненный слоистым недеформированным комплексом (ССК‐3)

One-Dimensional Electron Liquid in an Antiferromagnetic Environment: Spin Gap from Magnetic Correlations

We study a one-dimensional electron liquid coupled by a weak spin-exchange interaction to an antiferromagnetic spin-S ladder with n legs. A perturbative renormalization group analysis in the semiclassical limit reveals the opening of a spin gap, driven by the local magnetic correlations on the ladder. The effect, which we argue is present for any gapful ladder or gapless ladder with $nS\gg 1$, is enhanced by the repulsive interaction among the conduction electrons but is insensitive to the sign of the spin exchange interaction with the ladder. Possible implications for the striped phases of the cuprates are discussed.Comment: 5 pages, 1 figure, to appear in Phys. Rev. Let

Mean field approach to antiferromagnetic domains in the doped Hubbard model

We present a restricted path integral approach to the 2D and 3D repulsive Hubbard model. In this approach the partition function is approximated by restricting the summation over all states to a (small) subclass which is chosen such as to well represent the important states. This procedure generalizes mean field theory and can be systematically improved by including more states or fluctuations. We analyze in detail the simplest of these approximations which corresponds to summing over states with local antiferromagnetic (AF) order. If in the states considered the AF order changes sufficiently little in space and time, the path integral becomes a finite dimensional integral for which the saddle point evaluation is exact. This leads to generalized mean field equations allowing for the possibility of more than one relevant saddle points. In a big parameter regime (both in temperature and filling), we find that this integral has {\em two} relevant saddle points, one corresponding to finite AF order and the other without. These degenerate saddle points describe a phase of AF ordered fermions coexisting with free, metallic fermions. We argue that this mixed phase is a simple mean field description of a variety of possible inhomogeneous states, appropriate on length scales where these states appear homogeneous. We sketch systematic refinements of this approximation which can give more detailed descriptions of the system.Comment: 14 pages RevTex, 6 postscript figures included using eps

DEPTOR Expression Correlates with Muscle Protein Synthesis

Mammalian target of rapamycin (mTOR) has long been declared a focal point of muscle protein synthesis. mTORC1 (an mTOR complex consisting of mTOR, raptor, PRAS40, and mLST8) has been associated with regulation of protein translation in muscle, altering expression and activity levels of key downstream targets S6K1 and eIF-4E-BP1. mTORC1 has been shown to be affected by various stimuli, including nutritional status, growth factors, and mechanical loading. But in past incidents we have found disconnects in muscle protein synthesis and mTOR signaling, stimulating discussions that mTOR content and activation alone may not be able to fully account for muscle protein synthesis. Gaining popularity as a target for anti-cancer therapies, we became interested in DEPTOR, an endogenous inhibitor of mTORC1. Pharmacological inhibition of DEPTOR in cell culture and mouse studies has displayed increases of anabolic signaling in response to atrophic circumstances. We present two unique catabolic conditions in which we explore DEPTOR expression and muscle protein synthesis and demonstrate the first known data proposing that DEPTOR expression is not only influenced by physiological stimuli, including mechanical loading and insulin sensitivity, but that DEPTOR expression strongly correlates with 24-hr cumulative muscle protein synthesis rates. In one study, male Sprague Dawley rats were subjected to various conditions of musculoskeletal unloading, reloading, and overload, in which hindlimb unloading (HU) was utilized to mimic chronic disuse atrophy (28-d), followed by ambulatory reloading (56-d post HU) with and without the addition of resistance exercise prescribed to assist in recovery (3 sessions/wk for 7-wks; progressive increases in added resistance up to ~60% BW). DEPTOR expression was assessed via Immunoblotting. 24-hr cumulative muscle protein synthesis (FSR) was measured via stable isotope labeling and quantified by gas chromatogram/mass spectrometry. DEPTOR demonstrated a strong negative correlation with FSR in the gastrocnemius (r = - 0.93261; p \u3c0.01). In our second study, male obese Zucker rats were divided into their lean and obese phenotypes, as well as placed into sedentary and resistance exercised groups. DEPTOR and FSR were assessed as described above following operant conditioning and four progressive exercise sessions over 9-d. Gastrocnemius DEPTOR/FSR was again significant (r = - 0.75723; p\u3c0.01). Collectively, these results are the first to associate physiologic changes in DEPTOR expression with alterations of FSR, which may have important implications towards the design of therapeutic targets for the control of muscle mass or in evaluating muscle anabolism

Resistance scaling at the Kosterlitz-Thouless transition

We study the linear resistance at the Kosterlitz-Thouless transition by Monte Carlo simulation of vortex dynamics. Finite size scaling analysis of our data show excellent agreement with scaling properties of the Kosterlitz-Thouless transition. We also compare our results for the linear resistance with experiments. By adjusting the vortex chemical potential to an optimum value, the resistance at temperatures above the transition temperature agrees well with experiments over many decades.Comment: 7 pages, 4 postscript figures included, LATEX, KTH-CMT-94-00

Phase diagrams of the 2D t-t'-U Hubbard model from an extended mean field method

It is well-known from unrestricted Hartree-Fock computations that the 2D Hubbard model does not have homogeneous mean field states in significant regions of parameter space away from half filling. This is incompatible with standard mean field theory. We present a simple extension of the mean field method that avoids this problem. As in standard mean field theory, we restrict Hartree-Fock theory to simple translation invariant states describing antiferromagnetism (AF), ferromagnetism (F) and paramagnetism (P), but we use an improved method to implement the doping constraint allowing us to detect when a phase separated state is energetically preferred, e.g. AF and F coexisting at the same time. We find that such mixed phases occur in significant parts of the phase diagrams, making them much richer than the ones from standard mean field theory. Our results for the 2D t-t'-U Hubbard model demonstrate the importance of band structure effects.Comment: 6 pages, 5 figure

Monte Carlo calculation of the current-voltage characteristics of a two dimensional lattice Coulomb gas

We have studied the nonlinear current-voltage characteristic of a two dimensional lattice Coulomb gas by Monte Carlo simulation. We present three different determinations of the power-law exponent $a(T)$ of the nonlinear current-voltage characteristic, $V \sim I^{a(T)+1}$. The determinations rely on both equilibrium and non-equilibrium simulations. We find good agreement between the different determinations, and our results also agree closely with experimental results for Hg-Xe thin film superconductors and for certain single crystal thin-film high temperature superconductors.Comment: late

Current--Voltage Characteristics of Two--Dimensional Vortex Glass Models

We have performed Monte Carlo simulations to determine current--voltage characteristics of two different vortex glass models in two dimensions. The results confirm the conclusions of earlier studies that there is a transition at $T=0$. In addition we find that, as $T\to 0$, the linear resistance vanishes exponentially, and the current scale, $J_{nl}$, where non-linearities appear in the $I$--$V$ characteristics varies roughly as $T^3$, quite different from the predictions of conventional flux creep theory, $J_{nl} \sim T$. The results for the two models agree quite well with each other, and also agree fairly well with recent experiments on very thin films of YBCO.Comment: 18 pages with 10 figures available upon request from R. A. Hyman at [email protected]. The only change in the new version is the deletion of an unimportant comment.IUCM94-01

Monte Carlo simulation of a two-dimensional continuum Coulomb gas

We study the classical two-dimensional Coulomb gas model for thermal vortex fluctuations in thin superconducting/superfluid films by Monte Carlo simulation of a grand canonical vortex ensemble defined on a continuum. The Kosterlitz-Thouless transition is well understood at low vortex density, but at high vortex density the nature of the phase diagram and of the vortex phase transition is less clear. From our Monte Carlo data we construct phase diagrams for the 2D Coulomb gas without any restrictions on the vortex density. For negative vortex chemical potential (positive vortex core energy) we always find a Kosterlitz-Thouless transition. Only if the Coulomb interaction is supplemented with a short-distance repulsion, a first order transition line is found, above some positive value of the vortex chemical potential.Comment: 10 pages RevTeX, 7 postscript figures included using eps