No abstract

Morphological characteristics of the southwestern deep-depression East Sea have been defined based on the subdivision into co-origin surfaces. The results show that, the study area has 16 morphological units, including: Horizontal surface, slightly inclined surface, continental shelf accumulation, 200÷300 m depth; The surface is slightly inclined and wavy accumulates the outer shelf, 300÷700 m deep; Horizontal surface, abrasive, 500÷700 m (Guyot); Abrasive horizontal surface (Guyot), depth 1,300÷1,600 m; Abrasive horizontal surface (Guyot), depth -2,000 m; The surface of the ancient volcanic crest is distributed at different depths; Young volcanic surface, 1,200÷3,000 m deep; Wavy, accumulative plain, continental rise, 1,100÷1,800 m deep; Plain transport - accumulation plain, depth 1,100÷2,300 m; The smooth plain transports accumulates, depth 2,300÷3,000 m; The plain is divided by underground hills and mountains in the north, 2,000÷2,600 m deep; The plain is strongly dissected of underground mountains, 1,700÷2,600 m deep; Deep depression surface splits; Tectonic slope surface, continental slope 800÷1,400 m depth; Slope surface of the Northwestern underground mountain range 1,800÷2,600 m; Slope surface of the Southeastern underground mountain range 2000÷2900 m. Based on the morphological characteristics of the study area, field investigation, and analytical results allowed us to capture the potential areas of the Fe - Mn nodule and crust, namely: morphological units such as Guyot, young volcanic surface are supposed to be the prospect of the Fe - Mn crust while the deepwater surfaces demonstrate favorable place for Fe - Mn nodule can produce accumulation.

Twenty marine sediment samples have been collected in the Quaternary sediments in the southwest deep-depression East Sea region to study the foraminifera’s characterization. By analyzing foraminifer components under a microscope and taking photos under SEM, the authors determined that foraminifera fossils in the research area belonged to 01 sub-ordo as per the classification system proposed by Loeblich A.R. and Tappan H., which is Globigerinina Delage and Hérouard, 1896 sub-ordo, including four families, ten genera and 24 species. 04 families are Globigerinidae (06 genera and 13 species), Globorotaliidae (with two genera and nine species), Pulleniatidae (one genus and one species), and Catapsydracidae (one genus and one species). They all belong to the planktonic foraminifer group, living in the deep sea. Their indicator ages range from Miocene to Recent.

The Tam Ky - Phuoc Son suture zone (TPSZ) is located in central Indochina and is referred to as a amalgamation site between the Truong Son and Kon Tum terranes during the early Paleozoic. The amphibolite and ultramafic rocks within the region were considered as a part of the Tam Ky - Phuoc Son ophiolitic complex. In this study, the authors present results of the U - Pb dating and trace element composition of the zircon grains derived from a granodioritic sample collected in the G18 gold mine in Quang Nam province in order to clarify the timing of magma emplacement and tectonic setting. The U - Pb dating data indicates that the granodioritic rocks formed at 447,4±2,9 Ma while the U/Yb ratio is ̴1 (average: 1.32) and the Sc/Yb ratio is ̴ 1.04, high Hf content (Average Hf: 10937 ppm) and low Yb content (Average Yb: 308 ppm). These geochemical values are comparable with the zircon, which is formed in the continental magmatic arc. Combination with the pre - existing data allowed us to confirm the existence of two contrast magma members in the North Kontum massif: The Middle Cambrian island arc complex and the Middle Ordovician continental complex.

Characteristics of sediment provenance in the southwestern East Sea The southwestern East Sea is a significant area for investigating marine geology and it has drawn many attentions from geoscientists. In this study, clay mineral assemblages of some sediment cores derived from the southwestern East Sea, which were conducted in previous studies were used to review characterization of sediment provenance in this area. Sediment compositions in the southwestern East Sea consist mostly of smectite (11÷58%), illite (19÷45%), and less abundance kaolinite (11÷29%), chlorite (10÷25%). Based on clay mineral assemblages, provenance analysis indicates that the Mekong River can mainly transport terrigenous sediments to the southwestern East Sea. Illite and chlorite have likely been reduced by physical weathering of the metamorphic and granitic rocks in the Tibetan Plateau. Kaolinite has primarily been released by chemical erosion of the K-feldspar rich bed rocks in the middle part of the Mekong Basin. However, smectite has been basically derived by chemical weathering of the parent basaltic rock in the middle to lower reaches of the Mekong Basin.