Journal of Asian Earth Sciences: X最新文献

In the northwestern Korean Peninsula, Cretaceous volcanic rocks are composed of andesite, andesite-dacite and rhyolite intercalated with terrigenous clastic rocks. Zircon grains selected from these rocks are authigenic zircons with obvious crystal edges and oscillatory zoning, their Th/U ratios being generally larger than 0.4 (0.16–2.22), indicating magmatic origin. Most rocks were formed at Early Cretaceous Albian (113–103 Ma) and partially, at late Aptian, Prior to this time magmatism took place at 125 Ma and 135 Ma. All the negative ε_Hf(t) values mean that these magma sources were contaminated by crust materials or derived from enriched mantle. Volcanic rocks belong to calc-alkaline series and partially to peraluminous series with relatively high alkali content. Chondrite-normalized REE patterns display right-lean LREE rich type and Primitive-mantle-normalized REE patterns do obvious negative anomalies in LILE (Ba, Sr), HFSE (Nb, Ta, P, Zr, Ti), but obvious positive anomalies in LIL (Rb, Pb) and HFS (Th, U, Nd). These volcanic rocks were formed in continental arc setting and their geochemical properties being similar to those of arc ADR (normal Island-Arc Andesite-Dacite-Rhyolite) suite rather than those of adakite. In the Late Early Cretaceous, west area of northeastern Asia including western Liaoning, China was in extensional setting but east area of northeastern Asia including northwestern Korean Peninsula, Jihei, eastern China and Far East areas, Russia were in continental arc setting.

The age and character of the main unconformities offshore Palawan is resolved, and their history reviewed. Some very deep and very shallow unconformities have insufficient well data, but from the Oligocene to Late Miocene times a series of unconformities can be dated, characterised and correlated regionally to help develop a new tectono-stratigraphic framework. This framework does not support the widely cited idea of Early Miocene subduction of a Proto-South China Sea plate followed by collision over a plate suture.

The absence or very weak expression of a Base Miocene Unconformity (c. 24 Ma), so strongly expressed across northern Borneo, also suggests a major revision of tectonic models is required. In spite of many cited reports, there is no evidence for an unconformity in the later Early Miocene (c. 17 to 15 Ma), which was a period of gradually increasing compression and uplift. The main mid-Neogene seismic unconformity is the Red Unconformity dated at about 12–13 Ma (equivalent to the DRU of Sabah). This was when the uplift of a foreland over-thrust system paused, and a locally erosional surface was rapidly transgressed.

This review describes the neglect of analytical sciences that remain a crucial part of basic geological studies.

The Chanthaburi, Pliew, Klathing, Khao Cha Mao, and Khao Hin Son granitic bodies in Chanthaburi and Chachoengsao provinces in southeastern Thailand, which are located on the southwestern side of the Mae Ping Fault and eastern side of the Klaeng Fault, were investigated. In this study, magnetic susceptibility measurements, whole-rock chemical composition and Nd-Sr isotope analyses, and zircon U-Pb dating were conducted on these granitic bodies. The surveyed granitic rocks are classified as I- to A-type granites, are of the ilmenite series, and show clearly negative Eu anomalies, which suggest they formed under reducing conditions. Nd-Sr isotope ratios indicate continental crust material involvement in the formation of these granite bodies. The magnetic and geochemical signatures are similar to those of granite bodies in southwestern Cambodia. The study area is thus considered an extensional area of southwestern Cambodia, corresponding to the Sukhothai Zone (the Chanthaburi-Kampong Chhnang Zone). Zircon U-Pb dating yields ages of 208–214 Ma (the Late Triassic) for granite bodies except for the Khao Cha Mao granitic body, which dates to 55 Ma. The former age corresponds to the collision time of the Sibumasu and Indochina terranes, and the latter age is likely related to the collision time of the Indian and Eurasian continents.