泰国普龙矽卡岩型铜金矿床闪长岩锆石U-Pb定年及意义

泰国普龙矽卡岩铜金矿床是琅勃拉邦-黎府铜金多金属成矿带内一个大型矽卡岩铜金矿床。为了厘定普龙矽卡岩型铜金矿床成岩成矿时代、探讨其矿床成因,本文开展了与矽卡岩化密切相关的闪长岩锆石LA-ICP-MS U-Pb年代学研究。研究表明,普龙铜金矿成矿时代为240.6±1.2Ma,与闪长岩结晶年龄一致。结合前人研究成果,认为琅勃拉邦-黎府铜金多金属成矿带在晚二叠世—早三叠世发生了一次重要的斑岩-矽卡岩-热液铜金成矿事件。     

Mountain building across a lithospheric boundary during arc construction: The Cretaceous Peninsular Ranges batholith in the Sierra San Pedro Martir of Baja California, Mexico

The Jura-Cretaceous Peninsular Ranges batholith (PRB) of Southern and Baja California contains a remarkable example of variation in crustal composition and structure across a batholith-parallel lithospheric-scale discontinuity. This lithospheric boundary between western oceanic-floored and eastern continental-floored crust influenced contractional deformation, arc magmatism, and differential exhumation of western and eastern zones in the batholith during its evolution.In the Sierra San Pedro Martir of Baja California, Mexico, a ca. 20 km wide, doubly vergent fan structure occurs across the PRB basement transition that consists of inward-dipping mylonite thrust sheets on the sides of the fan that gradually transition to a steeply-dipping tectonized zone in the center. A dramatic inverted metamorphic gradient occurs on the western side of this structure where mid-crustal amphibolite metamorphic grade rocks with peak pressures of 5–6 kbar in the center of the fan were thrust over upper-crustal sub-greenschist grade rocks (peak pressures < 2 kbar) in the western zone footwall. An inverted but smaller gradient occurs on the eastern side of the structure where rocks of the fan interior have been thrust eastwards over amphibolite to upper greenschist grade rocks (peak pressures 4–5 kbar).Gradients in cooling ages determined by ⁴⁰Ar/³⁹Ar biotite and K-feldspar and apatite fission track methods coupled with U–Pb zircon ages and Al in hornblende thermobarometry studies on plutons across this zone indicate that structures focused along the transition zone between contrasting lithosphere in the PRB accommodated nearly 15 km of the differential exhumation of western and eastern basement in the orogen. The western zone of the batholith was a major forearc depo-center for thick clastic sequences derived from the uplifting eastern PRB and remained at low average elevation during the Late Cretaceous and Paleogene. In contrast the eastern zone experienced dramatic uplift subsequent to achieving a crustal thickness in excess of 55 km by mid-Cretaceous time. This region had the isostatic potential for 4–5 km surface elevations, and likely formed a topographically high orogenic plateau. Exhumation of the fan structure initiated after 100 Ma and was largely complete by 85 Ma. Eastward-migrating unroofing of the rest of the eastern PRB continued into the Paleogene.A variety of factors were responsible for exhumation in this region. Structural thickening of the eastern zone of the orogen resulted from more than 30 million years of episodic contractional deformation in the fan structure, much of which followed island arc accretion of the western zone along this segment of the batholith. An episode of voluminous magmatism involving the intrusion of the 99–92 Ma La Posta-type magmatic suite across the eastern zone of the PRB triggered exhumation in the fan structure. Denudation in this region appears to have been solely by erosion; no evidence has been found for extensional tectonics during this time. This arc orogen demonstrates the important influence of inherited tectonic boundaries in controlling the spatial distribution of structural thickening and magmatism. It also displays the complex interrelationships among structural thickening, exhumation, and the role of magmatism in triggering exhumation episodes within orogens.     

New Evidence of Sauropod Dinosaurs from the Early Jurassic Period of Thailand

The oldest dinosaur assemblages of Thailand deposit in continental sedimentary rocks of the Nam Phong Formation. Not only Isanosaurus attavipatchi was discovered but at least two more species of basal sauropods were found. A partial skeleton from Phu Hin Tan locality refers to sauropod taxon A. It is different from Isanosaurus and shares some characteristics with basal sauropods in the Early Jurassic. The sauropod taxon B was found in Non Sra Ard locality. Base on postcranial skeleton, sauropod taxon B shares some characteristics of the family Vulcanodontidae. Moreover, several fragments of the sauropods specimen are also found in Pha Khok Wang Yang and Phu Noi localities. All of the evidences above indicate that there are a highly diversity of sauropods in the Nam Phong Formation. At least three sauropod species (including Isanosaurus) were found in the Nam Phong formation. The issue about the age of the Nam Phong has been debated for a long time between the Triassic and Jurassic age. All of sauropodomorphs, in this study, are more likely the Early Jurassic period dinosaurs than the Triassic period dinosaurs. And they have deposited in the upper part of Nam Phong Formation.     

Climate change and groundwater resources in Thailand

The average temperature of Thailand is projected to increase by 2-3 °C, and the annual rainfall is projected to increase by 25% and up to 50% in certain areas. The climate change in future is expected to provide changes in hydrological cycle and therefore impacts the groundwater resources too. In this study, we analyzed the general climate change trends and reviewed the groundwater conditions of Thailand. The climate changes, hydrologic variability and the impact of climate change on groundwater sustainability are also discussed based on a national groundwater monitoring program. Currently, there are 864 groundwater monitoring stations and 1 524 monitoring wells installed in Thailand. Moreover, the impact of climate change on groundwater-dependent systems and sectors is also discussed according to certain case studies, such as saline water intrusion in coastal and inland areas. Managing aquifer recharge and other projects are examples of groundwater adaptation project for the future.     

Dinosaur footprint assemblage from the Lower Cretaceous Khok Kruat Formation,Khorat Group,northeastern Thailand

The Khok Kruat Formation is the upper part of the Khorat Group, which consists of upper Lower Cretaceous non-marine sedimentary rocks in northeastern Thailand. Many dinosaur footprints have been known from the upper Lower Cretaceous (Aptian–Albian) Khok Kruat Formation at the Huai Dam Chum (Tha Uthen) site, northeastern Thailand. Approximately 600 tracks occur in thin mudstone layer of the northern part of the outcrop at the Huai Dam Chum track site. Two types of footprints, small-sized theropod and crocodylomorph are imprinted with mud cracks and ripple marks on the thin mud layer. Most of footprints are referred to cf. Asianopodus, and are imprinted by small-sized theropoda, probably ornithomimosauria. Theropod tracks are mainly separated into two groups, Group A and Group B. From ichnological viewpoints, the small-sized theropod track assemblage indicates the herd behaviour and its idiosyncratic group composition. In particular, the histogram of size-frequency measurements of Group A shows the anomalous bimodal distribution. We consider that there are two hypotheses; the first one is due to the male-female difference, and the second is a result of the different growing stage.     

Towards an improved understanding of erosion rates and tidal notch development on limestone coasts in the Tropics: 10 years of micro‐erosion meter measurements,Phang Nga Bay,Thailand

Knowledge and understanding of shore platform erosion and tidal notch development in the tropics and subtropics relies mainly on short‐term studies conducted on recently deposited carbonate rocks, predominantly Holocene and Quaternary reef limestones and aeolianites. This paper presents erosion rates, measured over a 10 year period on notches and platforms developed on the Permian, Ratburi limestone at Phang Nga Bay, Thailand. In so doing it contributes to informing a particular knowledge gap in our understanding of the erosion dynamics of shore platform and tidal notch development in the tropics and subtropics – notch erosion rates on relatively hard, ancient limestones measured directly on the rock surface using a micro‐erosion meter (MEM) over time periods of a decade or more. The average intertidal erosion rate of 0.231 mm/yr is lower than erosion rates measured over 2–3 years on recent, weaker carbonate rocks. Average erosion rates at Phang Nga vary according to location and site and are, in rank order from highest to lowest: Mid‐platform (0.324 mm/yr) > Notch floor (0.289 mm/yr) > Rear notch wall (0.228 mm/yr) > Lower platform (0.140 mm/yr) > Notch roof (0.107 mm/yr) and Supratidal (0.095 mm/yr). The micro‐relief of the eroding rock surfaces in each of these positions exhibits marked differences that are seemingly associated with differences in dominant physical and bio‐erosion processes. The results begin to help inform knowledge of longer term shore platform erosion dynamics, models of marine notch development and have implications for the use of marine notches as indicators of changes in sea level and the duration of past sea levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Fossil mollusc-faunas: Their bearing on the Holocene evolution of the Lower Central Plain of Bangkok (Thailand)

In this work, fossil molluscan assemblages are analyzed in order to reconstruct the evolution of the Northern Gulf of Thailand during the Holocene. The marine sediments (Bangkok Clay Formation) of the Lower Central Plain of Bangkok and the coastal plain of Phetchaburi were sampled at 16 localities, obtaining fossil shells and mangrove peat whose ¹⁴C ages range from 9000 to 2000 CYBP. A statistical treatment of abundance data returned four major groups, namely the Dendostrea rosacea association (intertidal mud), the Corbula fortisulcata–Mactra luzonica association (shallow infralittoral sandy mud), the Nuculana mauritiana–Timoclea scabra association (infralittoral sand spit) and the Timoclea scabra–Arcopagia pudica association (infralittoral mud). The data allowed both a stratigraphic correlation along two transects covering all of the Holocene basin and the creation of digitalized maps showing the presumable extension of the Thai paleogulf around the apex of Flandrian transgression event (about 5500 CYBP).     

Diatomaceous sedimentation in the Tertiary Lampang Basin, Northern Thailand

The Lampang Basin is the second largest Tertiary graben in northern Thailand and was formed in response to the Himalayan orogeny. Deposition started with Miocene sandstone, lignite, mudstone, shale and oil shale of the Mae Sot Formation, which gave way to Pliocene diatomite, diatomaceous clay and silty clay of the Ko Kha Formation, with coarse clastics being restricted to the basin margins. Secondary iron-staining and iron-rich nodules are also common in the latter formation.Diatoms only occur in the Ko Kha Formation, where they are abundant and well-preserved. Five assemblages, indicative of fresh to moderately alkaline water, are present. These floras are variously dominated by Aulacoseira granulata, A. granulata var. valida, A. agassizi, A goetzeana, A. ambigua, A. italica var. bacilligera and A. italica var. tenuissima. Pennate species are present, but infrequent.During the Pliocene, in the Ban Pa Muang area, non-diatomaceous lacustrine sediments were initially laid down. These gave way to the deposition of diatomaceous clays and diatomites dominated by A. granulata and A. agassizi, which flourished in the deeper and shallower sectors (respectively) of a fresh water body. The palaeolake then became mildly alkaline, with a flora dominated by A. granulata var. valida. Shallow, fresh conditions followed, characterised by varied Aulacoseira diatoms, before the lake again became deeper. This latter phase may be related to increased river recharge.     

斑节对虾两个种群生化遗传变异的研究

采用聚丙烯酰胺梯度凝胶垂直板电泳的方法,对斑节对虾(Penaeus monodon Fabricius )2个种群的苹果酸酶(ME),苹果酸脱氢酶(MDH),谷氨酸脱氢酶(GDH),乳酸脱氢酶(IDH),磷酸葡萄糖变位酶(PGM),碱性磷酸酶(ALP),酸性磷酸酶(AcP),超氧化物歧化酶(SOD)和酯酶(EST)等9种同工酶做了对比分析。结果表明,在2个种群的9种同工酶系统的18个位点中,三亚种群(中国)有9个为多态位点,占位点总数的50．0％;纳颉岛种群(泰国)有10个是多态位点,占态位点总数的55．6％。其中PGN-3位点在三亚种群中只出现纯合型,在纳颉岛种群中只出现杂合型;而MDH-1和ALP-3位点在三亚种群中只出现杂合型,在纳颉岛种群中只出现纯合型。三亚种群和纳颉岛种群的平均杂合度分别是0．3596和0．3254,两者的遗传距离为0．0620。     

泰国湾第四纪准层序建造及气候控制的旋回性

泰国湾第四系显示出很好的旋回性。通过高分辨率二维地震(布玛)剖面图及工程钻井资料,共识别出8个准层序。在典型准层序中,沉积物自下而上,从海相泥沉积逐渐过渡为泛滥平原沉积。在每个准层序顶部都发育下切河体系及古土壤层,说明在每个准层序形成之后,都曾暴露过地表并遭受到侵蚀。每个准层序都代表一个海进和海退的过程。这些准层序的厚度为6～22m不等,平均厚度13m左右。通过与第四纪氧同位素曲线对比得出,这8个旋回的形成年代可追溯到距今730～10ka,平均91ka为一个循环周期,表明这些旋回应该是由气候因素所驱使的海平面升降导致的。该频率的气候变化周期相当于Milankovitch旋回中地球围绕太阳运动椭球体偏心率的变化周期,因此,在更早的地质历史时期中,类似的旋回也应该存在,并具有全球可对比性。