Evolution of the Appalachian orogen spanned the Paleozoic and Mesozoic Eras. Within the confines of the northern Appalachians of the United States (the New England States - Maine, New Hampshire, Vermont, Massachusetts, Connecticut and Rhode Island - and New York), the sequence of known major Appalachian tectonic events is late Proterozoic rifting of the protoNorth American craton; Ordovician subduction accompanied by destruction of the Iapetus Ocean and by obduction of tectonostratigraphic sequences; Devonian deformation, accretion, plutonism, and metamorphism, of uncertain plate tectonic context but likely related to a continent continentcollision; formation of late Carboniferous transtensive (oblique strikeslip) basins in which coal formed; and late Carboniferous to Permian thermal, plutonic, and metamorphic events. During the Mesozoic, the New England Appalachians underwent crustal extension associated with both alkalic and tholeiitic magmatism. These extensional processes (11-7, V-l)~/ reflect the opening of the North Atlantic Ocean and the creation of a passive margin, which remains today.<...>

В работе на примере Южного Урала и Аппалач рассмотрено геологическое строение крупных полей пород офиолитового ряда, расположенных в краевых частях древных платформ, и показано, что такие поля представляют собой аллотонные массы, шарьированные в пределы платформ в результате поддвига последних под эвгеосинклинальные толщи. Рассмотрен механизм формриования покровных структур в связи с представлениями "глобальной тектоники плит". Большое место уделено методам палеотектонических и фациольных реконструкций в областях, характеризующихся покровным строением. На этой основе дана схема тектонического развития областей стыка платформ и эвгеосинклиналей.

Монография посвящена выявлению главных структурно-вещественных закономерностей истории развития начальных этапов рифейско-палеозойской (неогейской), раннепротерозойской и позднеархейской тектонических эпох, когда происходило заложение новых структурных планов неогейского, афебского и киватинского глобальных тектонических этажей и формирование оригинальных деструктивных структурно-вещественных комплексов вследствие разрушения (деструкции) ранее сформированных кратонов в пределах континентов. Проблема рассмотрена на примерах Аппалачей, юга Восточной Сибири и некоторых районов Канадского, Индостанского и Южно-Африканского щитов. Исследована афебская структура Канадского щита, эталонная для этого этажа, установлен гомологический ряд деструктивных комплексов в истории материков.

Книга рассчитана на геологов, работающих в области тектоники и стратиграфии докембрия, магматических формаций, петрологии

Well-documented tectonic events in the central Appalachians of Pennsylvania are: (1) the early Paleozoic Taconian orogeny that occurred during convergence of Laurentian and the Chopawamsic-Wilmington complex magmatic arc over an east-dipping subduction zone, and resulted in intense metamorphism and deformation in the Piedmont, and (2) the late Paleozoic Alleghanian orogeny that resulted in the thrust and fold belt in the Valley and Ridge province and dextral shear zones in the Piedmont. Unlike the Paleozoic tectonic history for the northern and southern Appalachians, the north-central part of the orogen in Pennsylvania lacks evidence for Acadian deformation and metamorphism. The relative chronological order of deformation and metamorphic events in the eastern Piedmont of Pennsylvania, combined with published geochro-nology suggests the previously undocumented Acadian deformation possibly exists as a transcurrent conjugate shear zone pair.

Field, petrographic, microstructural and isotopic studies of mylonitic gneisses and associated pegmatites along the Hope Valley shear zone in southern Rhode Island indicate that late Palaeozoic deformation (c. 275 Ma)in this zone occurred at very high temperatures (>650
C). High-energy cuspate ⁄ lobate phase boundary microstructures, a predominance of equant to sub-equant grains with low internal lattice strain, and mixed phase distributions indicate that diffusion creep was an important and possibly predominant deformation mechanism. Field and petrographic evidence are consistent with the presence of an intergranular melt phase during deformation, some of which collected into syntectonic pegmatites. Rb ⁄ Sr isotopic analyses of tightly sampled pegmatites and wall rocks confirm that the pegmatites were derived as partial melts of the immediately adjacent, isotopically heterogeneous mylonitic gneisses. The presence of syntectonic interstitial melts is inferred to have permitted a switch from dislocation creep to melt-enhanced diffusion creep as the dominant mechanism in these relatively coarse-grained mylonitic gneisses (200–500 lm syn-deformational grain size). A switch to diffusion creep would lead to significant weakening, and may explain why the Hope Valley shear zone evolved into a major regional tectonic boundary. This work identifies conditions under which diffusion creep operates in naturally deformed granitic rocks and illuminates the deformation processes involved in the development of a tectonic boundary between two distinct Late Proterozoic (Avalonian)basement terranes.