Tectonic implication of Lower Cretaceous chromian spinel-bearing sandstones in Japan and Korea

金沢大学理工研究域自然システム学系In Japan and Korea, some Lower Cretaceous terrigenous clastic rocks yield detrital chromian spinels. These chromian spinels are divided into two groups: low-Ti and high-Ti. The Sanchu Group and the Yuno Formation in Japan have both groups, whereas the Nagashiba Formation in Japan and the Jinju Formation in Korea have only the low-Ti spinels. High-Ti spinels are thought to have originated in intraplate-type basalt. Low-Ti spinels (higher than 0.6 Cr) were probably derived from peridotites, which are highly correlated with an arc setting derivation and possibly with a forearc setting derivation. Low-Ti spinels are seen in the Sanchu Group, the Nagashiba Formation and the Jinju Formation. Low-Ti spinels from the Yuno Formation are characterized by low Cr (less than 0.6) and these chromian spinels appear to have been derived from oceanic mantle-type peridotite, including backarc. According to maps reconstructing the pre-Sea of Japan configuration of the Japanese Islands and the Korean Peninsula, the Korean Cretaceous basin was comparatively close to the Southwest Japan depositional basins. It is possible that these Lower Cretaceous systems were sediments mainly in the forearc and partly in the backarc regions. The peridotite might have infiltrated along major tectonic zones such as the Kurosegawa Tectonic Zone (=serpentinite melange zone) in which left lateral movement prevailed during the Early Cretaceous

Early cretaceous paleogeography of Korea and Southwest Japan inferred from occurrence of detrital chromian spinels

The Sindong Group was deposited in the north-south trending half-graben Nakdong Trough, southern Korean peninsula. The occurrence of detrital chromian spinels from the Jinju Formation of the Sindong Group in the Gyeongsang Basin means that the mafic to ultramafic rocks were exposed in its provenance. The chromian spinels from the Jinju Formation are characterized by extremely low TiO2 and Fe3+. Moreover, their range of Cr# is from 0.45 to 0.80 and makes a single trend with Mg#. The chemistry of chromian spinels implies that the source rocks for chromian spinels were peridotites or serpentinites, which originated in the mantle wedge. To more narrowly constrain their source rocks, the Ulsan and Andong serpentinites exposed in the Gyeongsang Basin were examined petrographically. Chromian spinels in the Andong serpentinite differ from those of the Jinju Formation and those in the Ulsan serpentinite partly resemble them. Furthermore, the Jinju chromian spinel suite is similar to the detrital chromian spinels from the Mesozoic sediments in the Circum-Hida Tectonic zone, which includes the Nagato Tectonic zone in Southwest Japan and the Joetsu Belt in Northeast Japan. This suggests that the basement rocks, which were located along the main fault bounding the eastern edge of the Nakdong Trough, had exposures of peridotite or serpentinite. It is possible that the Nakdong Trough was directly adjacent to the Circum-Hida Tectonic zone before the opening of the Sea of Japan (East Sea). © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd

Missing ophiolitic rocks along the Mae Yuam Fault as the Gondwana-Tethys divide in north-west Thailand

Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son-Mae Sariang area, north-west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean-floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana-Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion. © 2004 Blackwell Publishing Asia Pty Ltd

Petrology of the Yugu peridotites in the Gyeonggi Massif, South Korea: Implications for its origin and hydration process

金沢大学理工研究域自然システム学系Peridotites exposed in the Yugu area in the Gyeonggi Massif, South Korea, near the boundary with the Okcheon Belt, exhibit mylonitic to strongly porphyroclastic textures, and are mostly spinel lherzolites. Subordinate dunites, harzburgites, and websterites are associated with the lherzolites. Amphiboles, often zoned from hornblende in the core to tremolite in the rim, are found only as neoblasts. Porphyroclasts have recorded equilibrium temperatures of about 1000°C, whereas neoblasts denote lower temperatures, about 800°C. Olivines are Fo 90-91 in lherzolites and Fo 91 in a dunite and a harzburgite. The Cr# (=Cr/(Cr + Al) atomic ratio) of spinels varies together with the Fo of olivines, being from 0.1 to 0.3 in lherzolites and around 0.5 in the dunite and harzburgite. The Na2O content of clinopyroxene porphyroclasts is relatively low, around 0.3 to 0.5 wt% in the most fertile lherzolite. The Yugu peridotites are similar in porphyroclast mineral chemistry not to continental spinel peridotites but to sub-arc or abyssal peridotites. Textural and mineralogical characteristics indicate the successive cooling with hydration from the upper mantle to crustal conditions for the Yugu peridotites. Almost all clinopyroxenes and amphiboles show the same U-shaped rare earth element (REE) patterns although the level is up to ten times higher for the latter. The hydration was associated with enrichment in light REE, resulting from either a slab-derived fluid or a fluid circulating in the crust. The mantle-wedge or abyssal peridotites were emplaced into the continental crust as the Yugu peridotite body during collision of continents to form a high-pressure metamorphic belt in the Gyeonggi Massif. The peridotites from the Gyeonggi Massif exhibit lower-pressure equilibration than peridotites, with or without garnets, from the Dabie-Sulu Collision Belt, China, which is possibly a westward extension of the Gyeonggi Massif. © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd

Early Permian ammonoids from the Kaeng Krachan Group of the Phatthalung-Hat Yai area, southern peninsular Thailand

An Early Permian small ammonoid fauna consisting of Neocrimites sp., Agathiceras suessi Gemmellaro, A. girtyi Bo¨se, Agathiceras? sp.,and Miklukhoceras sp. was found in nodules of a fine sandstone bed exposed in the Phatthalung-Hat Yai area of southern peninsular Thailand.The ammonoid-bearing bed belongs stratigraphically to the uppermost part of the Kaeng Krachan Group, which is essentially a clasticdominant, Late Carboniferous (?) to Early Permian stratigraphic unit, widely distributed in western and peninsular Thailand. This ammonoidfauna is considered to be of Bolorian (Kungurian) age and includes Agathiceras girtyi Bo¨se, which is described for the first time from Thailand. The present discovery of Bolorian ammonoids suggests that the uppermost part of the Kaeng Krachan Group is slightly younger than previously considered and around the latest Early Permian. This further implies that the continental margin environment of the Sibumasu Block drastically changed at around Bolorian time from a cool, clastic-dominant shelf condition to a temperate to subtropical, carbonate platform due to rapid northward drift after middle Artinskian rifting

Revised version of the Cenozoic Collision along the Zagros Orogen, Insights from Cr-spinel and Sandstone Modal Analyses

Geoscientists have always considered the Neyriz region, located along the Zagros Suture Zone, an important area of interest because of the outcrops of Neotethys ophiolitic rocks. We carried out a modal analysis of the Cenozoic sandstones and geochemistry of the detrital Cr-spinels at Neyriz region in order to determine their provenance and tectonic evolution in the proximal part of Zagros Basin. Our data shows a clear change in provenance from the Late Cretaceous onwards. As from the Late Cretaceous to Eocene, lithic grains are mostly chert and serpentinite; and higher Cr# values of the detrital Cr-spinel compositions indicate that they originate from the fore-arc peridotites and deposited in an accretionary prism setting during this period. From the Late Oligocene to the Miocene periods, volcaniclastic and carbonate lithic grains show an increasing trend, and in the Miocene, metasedimentary lithic grains appear in the sediments. Ophiolite obduction caused a narrow trough sub-basin to be formed parallel to the general trend of the Zagros Orogeny between the Arabian and Iranian plates in Oligocene. From the Miocene onwards, the axial metamorphic complex belt was uplifted in the upper plate. Therefore, the collision along the Zagros Suture Zone must have occurred in the Late Oligocene

Preface: Outline of IGCP 516

The International Geological Correlation Programme (IGCP) has progressed since 1972 under the sponsorship of the United Nations Educational, Scientific and Cultural Organization (UNESCO) and the International Union of Geological Sciences (IUGS). As one of the IGCP projects, IGCP 516 entitled "Geological Anatomy of East and South Asia: Paleogeography and Paleoenvironment in Eastern Tethys" was established as a successor project to 'Geodynamics of Gondwana-derived terranes in East Asia: 1998-2002' (IGCP 441) in 2005. In IGCP 441 and its preceeding projects (IGCP 224 and 321), our knowledge on the break-up of Gondwana and the basic geotectonic framework of East Asia expanded significantly. Participants in these projects have indentified the basic scenario for the rift-drift-amalgamation history of the main Gondwana-derived terranes including the timing of rifting and collision of the main continental fragments. The fundamental purpose of IGCP 516 is to gain insights into the paleogeography and paleoenvironment of the eastern Tethys. The framework of geodynamic processes has been established as mentioned above but the identification of, and interrelation between, terranes are still controversial. Knowledge concerning some terranes is also insufficient. To accomplish this purpose, the geological anatomy of East and South Asia, as well as Southeast Asia, has been investigated by IGCP 516 participants vigorously. Exchange of geological data and information among participants took place at the international symposia of IGCP 516 held in Tsukuba, Japan in 2005, Manila, the Philippines in 2006, Delhi, India in 2007, Bangkok, Thailand in 2008, Kunming, China in 2009 and Kuala Lumpur, Malaysia in 2010. The participating countries and regions were Australia, Bangladesh, China, India, Indonesia, Iran, Iraq, Italy, Japan, Jordan, Korea, Lao PDR, Malaysia, Mongolia, Myanmar, Pakistan, Philippines, Poland, Russia, Taiwan, Thailand, UK and USA

中生代付加体砕屑粒子の高精度後背地研究

科学研究費助成事業 研究成果報告書：基盤研究(C)2012-2015課題番号 : 2454049

西アジア先史時代の石材供給に関する地質学

科学研究費助成事業 研究成果報告書：新学術領域研究（研究領域提案型）2012-2016課題番号 : 2410100