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A Plate Tectonics Controversy -Do you still believe plate tectonics?- Michihei HOSHINO Published by E. G. Service Press, 2010, Sapporo, Japan. In Japanese with English abstract. Masahiro SHIBA September, 2010 Japanese Version  In Japan ordinary people have been taught that earthquakes and volcanic activity are caused by plate subduction. Plate tectonics (PT) has been promulgated by school textbooks and by the mass media, such as newspapers and television. Discussion of tectonics and paleogeography is currently based on the assumption that PT is correct. In Japan, several books and reviews recently published articles that blamed the critics of PT for the delay in acceptance of PT in Japanese geological communities. Prof. Hoshio published this book in response to these criticisms and to present his own opinions. In this book, the author asks whether or not PT is the ONLY hypothesis that can solve many problems in Earth science. He then introduces his original theory of the history of the Earth and analyses the background that has allowed PT to be widely accepted. He emphasizes that young people must be free from the PT dogma in Earth science, and encourages them to develop their own hypotheses and engage in open discussion with one another. The first chapter, "Birth of PT", describes the birth and tenets of PT. The second Chapter, "Test of the alleged observational facts”, presents contradictory evidence for the formation of mid-ocean ridges, trenches, ocean basin floors, continental drift theory, and the driving force of plate motion. In "History of the Earth", which constitutes chapter 3, the author briefly introduces his views on the history of the Earth, and the last chapter, "Background to PT popularity", discusses the scientific, ideological, and social background of PT. Chapter 2, which forms the core of the book, states that rocks constituting mid-ocean ridges do not always have the mid-ocean ridge-type basalt, and lists many finds of ancient and continental rocks. With regard to the rift valley, taking the East Africa - Red Sea rift belt as an example, he shows that the formation of its geographical features cannot be explained by PT. Concerning the trenches, he shows that: 1) there are many trenches which are not paired with a mid-ocean ridge, 2) the trench sediments are supplied from the land and their surface is generally undisturbed, and 3) there is no basaltic layer at the trench bottom. The area from the outer side of the trench to the oceanic marginal swell shows a tensional structure with alkaline basalts. Furthermore, he points out that in the oceanic marginal swell high heat flow and positive gravity anomalies are observed. He also points out that the slope angle of the earthquake zone along trenches varies, and the slope also changes with depth. Regarding the ocean basin floor, the oceanic crust has a three-layer structure. He discusses the problems with their formation: PT cannot explain the origin of the oceanic crust and intra-plate basaltic activity, and it also cannot explain why the depth of the Moho under the oceanic crust is at 11 km depth. He points out that the basalt of the second layer of oceanic crust does not show ages that match the age required by magnetic lineations, and that the magnetic quiet zone is also unexplainable by PT. In addition, continental rocks have been discovered in the ocean floor and oceanic volcanic islands, sometimes showing Late Proterozoic ages. He asserts that the difference in the thickness of the lithosphere in the West Pacific Ocean and the East Pacific Ocean was caused by the difference in the peneplanation level in the Latest Proterozoic Era. With regard to continental drift, taking the upheaval and the biogeography of the Himalayas and the Tibet as examples, he points out that the supposed collision with the Eurasian and the Indian continents is not in agreement with the time of elevation of the Himalayas. He says that the global biogeographical pattern is not due to continental drift; rather, the distribution of terrestrial biota since the Mesozoic Era was controlled by the submergence of land bridges due to rising sea levels. As regards the plate driving force, PT believers argue that the increase in plate density due to cooling generates a pull effect causing slabs to descend. He considers that the truth cannot be clarified unless they explain how the first spreading plate was produced and what the driving force of the first plate was. The author has studied the formation and history of the crust based on sea level, which formed an erosional base level simultaneously all over the world. In his book, "The Pacific Ocean" written in 1962, he said that the sea level rose by 2000 m after the late Miocene. In another book, "Eustasy in relation to orogenic stage" in 1975, he asserted that the sea level of the Middle Cretaceous was 4000 m beneath the present sea level. In "The Basaltic Stage", published in 1991, he divided the history of the Earth into the Granite Stage, the Transitional Stage, and the Basalt Stage, in ascending order. In "The expanding Earth" in 1998 and “Crustal development and sea level” in 2007, which summarized the formation and development of the crust, he completed his Earth microexpansion theory. Following the "The Basaltic Stage", his publications detailed the formation of plateaus, and geosynclinal-orogenic belts in the world in the Proterozoic and Paleozoic Eras, and elaborated his idea of the history of tectonics. In the early days we had difficulties fully understanding his grand, global geotectonic historical view stretching over several billion years, because we know only part of geology of the younger age confined to the narrow island arcs. Moreover, since we live near the present sea level, it was also difficult for us to imagine standing on a peneplain of the mid-Cretaceous Period (4 km beneath the present sea level) or the latest Proterozoic Era (11 km beneath), and also to understand the dynamics, the elevation of land and ocean basins, and the rising sea level as well. The book under review explains in plain language many geological problems found in mid-ocean ridges, trenches, and ocean basin floors that cannot be explained by PT. While we were reading this book, we were given many opportunities to ponder how the formation of these geographical features and geological structures has taken place. And we were at least able to understand the formation of plateaus and geosynclinal-orogenic belts in the Proterozoic and the Paleozoic Eras (Transitional Stage), and the subsequent formational process of remnant basins, island-trench systems and ridges. According to Hoshino, the Earth crust formed as follows: Eucrite chondorite gathered at the earliest stage of its birth, followed by enstatite chondorite, which formed the primeval Earth surface. The former formed the asthenosphere and the latter formed the uppermost part of the mantle (lower lithosphere). In the Granite Stage or the Archean Era, the former differentiated into atmosphere, hydrosphere and granitic crust. The latter has been rising as undifferentiated magma into the lower crust since the Proterozoic Era, especially becoming more active since Mesozoic. This magma made various kinds of basalt contaminated with ultra-mafic rocks, and elevated the upper crust by its intrusion. In the Transitional Stage (Proterozoic and Paleozoic), the activities of the layered igneous body that had been produced by the mixing of the Mg-rich ultra-mafic and Ca-rich mafic magmas formed elevated plateaus. The high temperature atmosphere that contained carbon dioxide and water steams in the Proterozoic Era eroded the elevated plateau violently, and built the vast peneplains. Then, sediments filled the seas surrounded by plateaus. As sea level rose, the plateau region became covered by shallow seas. Stromatolites grew thick in the shallow seas, forming dolomite, and emitted a vast amount of oxygen into the atmosphere simultaneously. The seas between plateaus were filled with thick sediments supplied from elevated plateaus, having become an incipient geosyncline. The bottom of many present-day geosynclinal belts is situated at a depth of about 50 km beneath the present sea level. Hoshino considers that this depth was at the sea bottom in the late Archean. In the latest Proterozoic Era (Glenvillian Stage), one billion years before the present, sea level had risen to about 11 km below the present level, and then the peneplains had been formed everywhere on Earth. The greater part of these peneplains constitutes the present Moho surface under the ocean floor. After that, as the surrounding geosynclinal-orogenic belts rose, the peneplains became the bottom of the old remnant basins. In the case of wide geosynclinal basins, when the central plateau, a composite of old and young plateaus, was elevated, reversed faults in the shape of a bidirectional petal were produced. After that, as the reverse faults have remained active, geosynclinal rock formation pushed out above the rims of the peneplanated plateaus (Moho surface under the ocean floor). The marginal sea (central plateau) - island arc (surrounding the geosynclinal-orogenic belt) - trench (compression zone) system was formed by this process. In the narrow geosynclinal basin without a central plateau, the elevation of the geosynclinal-orogenic belts has no extrusive rocks accompanied by reverse faults. The oceanic ridges consist of such geosynclinal-orogenic belts. The latest stage in the history of the Earth (basaltic stage) from the Mesozoic Era to the present is characterized by the activity of Ca-rich basaltic plutonic magmas. This resulted in the upheaval of land and ocean basins (epirogenic movement) with rising sea level. The basaltic plutonic rocks, mainly high-temperature and high-pressure magmas originated from the asthenosphere, increased in volume and produced linear deep faults along the weak belts of the lithosphere (Archean lineaments), and rose and intruded under the plateau basement by spreading horizontally. Magmas erupted on continents are plateau basalts, and those extruded on the sea floors covered the peneplanated Upper Proterozoic basement and formed the present-day oceanic crust. The deformed and elevated sedimentary layers formed island arcs and ridges. Due to the rise of the ocean basin floors caused by the addition of ocean basaltic layers since the Mesozoic, sea level has risen by 6 km. The author's view of the history of the Earth has led to an interesting development theory of the crust, in contrast to PT’s simple circular argument. His theory says that different igneous activity and crustal movement occurred uniquely for each stage - Granite Stage, Transitional Stage and Basaltic Stage from the birth of the Earth to the present - elevated the crust higher and higher and changed the Earth’s surface. We were able to catch a glimpse of part of the history of the Earth hidden under the continents and the ocean floors through this book, and we developed a new appreciation of the depth of Earth science and the charm of the theme, which are missing from the oversimplified PT hypothesis. |