Journal of Earth Science

Experimental Investigation on Low-Degree Dehydration Partial Melting of Biotite Gneiss and Phengite-Bearing Eclogite at 2 GPa

Qiang Liu, Yao Wu, Junfeng Zhang

2011, 22(6): 677-687. doi: 10.1007/s12583-011-0219-0

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Abstract:
The ultrahigh-pressure (UHP) eclogite and gneiss from the Dabie (大别)-Sulu (苏鲁) orogen experienced variable degrees of partial melting during exhumation. We report here dehydration partial melting experiments of biotite gneiss and phengite-bearing eclogite at 2 GPa and 800–950 ℃. Our results show that the partial melting of gneiss is associated with the breakdown of biotite into almandine-rich garnet starting at 900 °. About 10% granitic melt can be produced at 950 ℃. In contrast, the partial melting of phengite-bearing eclogite exists at slightly lower temperatures (800–850 ℃). The melt fraction is in general more in biotite gneiss than in phengite-bearing eclogite under similar pressure and temperature conditions. Both melts are rich in silica and alkali, but poor in FeO, MgO and CaO. These results suggest that low-degree partial melting of gneiss and eclogite is often associated with dehydration of hydrous mineral, such as micas. The dehydration temperature and melt composition can place important constraints on the partial melting phenomena (granitic leucosome and multi-phase mineral inclusions) recorded in UHP rocks.

Geochemistry of Middle Triassic Radiolarian Cherts from Northern Thailand: Implication for Depositional Environment

Hathaithip Thassanapak, Mongkol Udchachon, Chongpan Chonglakmani, Qinglai Feng

2011, 22(6): 688-703. doi: 10.1007/s12583-011-0220-7

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Abstract:
Geochemical analysis reveals that Middle Triassic radiolarian cherts from northern Thailand, including Chiang Dao, Lamphun and Den Chai, are of biogenic origin. These cherts present slightly high SiO₂ content which was possibly modified by diagenetic alteration and migration processes as indicated by negative correlation between SiO₂ and most of the other major elements. The relatively high content of Cr, Zr, Hf, Rb and Th and high positive correlation of these elements with Al and Ti from the majority of cherts suggest a close relation to terrigenous component. The Ce anomaly (Ce/Ce*) with geometric means ranging from 0.85 to 0.93 is compatible with that of continental margin composition (0.67–1.52) from Murray et al. (1990) which is also consistent with low Eu anomalies (Eu/Eu*, 0.91–0.94). Moreover, the slightly low ratios of La and Ce NASC normalized (La_n/Ce_n, 0.91–0.94) and the low LREE and HREE ratios in most of our samples (La_n/Yb_n, 0.62–0.85) are in agreement with the continental margin. The result from La_n/Ce_n vs. Al₂O₃/(Al₂O₃+Fe₂O₃) discrimination diagrams also supports the continental margin (residual basin, s. str.) interpretation. These geochemical results are compatible with geological evidence, which suggest that during the Middle Triassic, radiolarian cherts were deposited within a deeper part of a residual basin in which an accommodation space was possibly controlled by faults under extensional regime subsequent to Late Variscan (Permian) orogeny. Paleogeographically, the main Paleotethys which closed during Late Triassic should be located further to the west of these study localities. This scenario is in agreement with the current view of the Tethys in this part of the world.

Organic Carbon Isotope Records of Paleoclimatic Evolution since the Last Glacial Period in the Tangjia Region, Tibet

Lingkang Chen, Xulong Lai, Yinbing Zhao, Haixia Chen, Zhongyun Ni

2011, 22(6): 704-717. doi: 10.1007/s12583-011-0221-6

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Abstract:
We firstly present the description of the river terrace at Tangjia (唐家) Village in Lhasa, Tibet, collect soil samples, and select the climate indicators including δ¹³C, total organic carbon (TOC), and the Rb/Sr ratios to study its paleoclimate in this area. Ancient climate changes have been reconstructed since the last glacier period. The results show that the δ¹³C, TOC, and the Rb/Sr ratio are good indicators of ancient climate fluctuations. Paleoclimatic evolution in the Lhasa Tangjia region could be divided into seven stages. In stages II (11.7–10.2 kaB.P.) and IV (8.1–6.1 kaB.P.), δ¹³C was positive and TOC was high, indicating that the climates in these two stages were relatively warm and humid. In stages III (10.2–8.1 kaB.P.) and V (6.1–4.9 kaB.P.), δ¹³C showed cyclical fluctuations, but TOC exhibited less change, suggesting that the climates displayed variation on the millennial scale. Moreover, the climatic variations were on a century-long scale during the later Middle Holocene. Compared with δ¹³C from Sumxi Co (松木希错) and δ¹⁸O from the Guliya (古里雅) ice core, the study confirmed that four cold events occurred during the Holocene (9.4, 8.2, 5.4, and 4.2 kaB.P.). The climate indicators were limited to the river terrace based on the geological characteristics of the Lhasa region. Unexpectedly, δ¹³C was a sensitive indicator of climate change.

Geological and Geophysical Conditions for Potential Natural Gas Hydrate Resources in Southern South China Sea Waters

Hailing Liu, Yongjian Yao, Hui Deng

2011, 22(6): 718-725. doi: 10.1007/s12583-011-0222-5

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Abstract:
The water depth in Nansha (南沙) waters, which is located in the southern South China Sea, varies from 200 to 2 500 m, with a deep-water (> 500 m) area of 500 000 km2. In this region, there are many depositional basins with various structural features, prone to the accumulation of organic material. The temperature and pressure conditions in the deep-water environment are suitable for the preservation of gas hydrate. At several sites, we have recognized bottom-simulating reflectors (BSRs) from seismic data. Regional geology analyses show that the Nansha waters may have abundant gas hydrate prospects, especially in localities such as the Nansha trough and other deep-water basins of the central Nansha waters.

Synchronization Theory and Tungsten-Polymetallic Mineralization Distribution in the Qianlishan-Qitianling Area, Southern Hunan

Bing Li

2011, 22(6): 726-736. doi: 10.1007/s12583-011-0223-4

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Abstract:
Synchronization is an important frontier in contemporary nonlinear science. It has been developed and applied widely in the late 20th century. However, it has limited applications in geological science, especially in the study of mineralization. The ore formation of fluids is a problem of propagation of chemical waves and the generation of their spatiotemporal structures. Geological processes and spatiotemporal structures are the essence and core of all geological phenomena. Taking these ideas as guides, giving a new definition for "phase" in geochemical dynamics, and selecting the concentration data of 10 elements from stream-sediment samples on a 1: 50 000 scale, this article applies the synchronization theory to the study of the distribution of tungsten-polymetallic mineralization in the Qianlishan (千里山)-Qitianling (骑田岭) area in southern Hunan (湖南) which is one of the most important metallogenetic districts in the Nanling (南岭) region. The results show that there are large ore deposits in Shizhuyuan (柿竹园), Huangshaping (黄沙坪), Xianghualing (香花岭), Qitianling, and other areas, which verifies the present distribution of mineral resources in southern Hunan. Moreover, this article holds that the spatiotemporal synchronization of chemical waves plays an important role in the science of metallogenesis: it leads to the regional ore zoning centered at Qitianling, confirms that the Yanshan epoch is the chief oreforming epoch in southern Hunan, and predicts other prospective areas of specific ores.

Sequence Characteristics of Foreland Basin and Its Difference from Those of Other Types of Basin

Youliang Ji, Chunfu Pan, Yong Zhou, Rukai Zhu, Zhiyong Gao, Jieqi Yang, Gang Yu

2011, 22(6): 737-754. doi: 10.1007/s12583-011-0224-3

[Abstract](708) [FullText HTML] (102) [PDF 1694KB](26)

Abstract:
Based on the case history study of sequence stratigraphic framework, sequence model, and the controlling factors on sequence formation in the southern Junggar foreland basin, a contrasting comparison of the characteristics among the foreland basin, the faulted basin, and the sag basin is made in the aspects of sequence architecture, filling style, the controlling factors on sequence development, the migrations of basin center and depocenter, etc.. The current study results show that there are major differences and these are documented as follows. (1) The accommodation space in foreland basin is mainly created by the subsidence caused by thrusting and napping in the foothill belt, resulting in progradational-dominated parasequence sets in the foothill area and retrogradational parasequence sets in the ramp region. (2) The accommodation space in an open-lake system in faulted basin is mainly created by the activities of the basin margin faults; thus, tectonic sequences are formed. However, in the closed-lake system, the subaqueous accommodation is mainly controlled by climatic-influenced lake-level fluctuations, and climatic sequence is formed. (3) In sag basin, a closed-lake system is easily formed due to its generation often within the cratons and isolation from the sea, and its accommodation space creation is mainly controlled by climatic lake-level fluctuations; thus, the sequence architecture in sag basin is similar to that formed on the passive continental margin.

Nanpu Sag of the Bohai Bay Basin: A Transtensional Fault-Termination Basin

Xiaofeng Liu, Cuimei Zhang

2011, 22(6): 755-767. doi: 10.1007/s12583-011-0225-2

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Abstract:
The Nanpu (南堡) sag has previously been modeled as (1) a pull-apart basin, (2) a rift basin, without significant strike-slip deformation, and (3) a transtensional basin. We present a new model for the Nanpu sag in which the basin is a transtensional fault-termination basin. Although transtensional fault-termination basins is an important basin type, it is not as well studied as other classic basin types. On the base of 3D seismic data interpretation, the faults geometries and kinematics and their controls on depocenters are presented. The Nanpu sag is developed in the context of dextral transtension of the Bohai (渤海) Bay basin and attributed to a transtensional fault-termination basin. During deposition of the Es³-Es² members, the basin border Xi'nanzhuang (西南庄) fault and Baigezhuang (柏各庄) fault linked to a mixed normal and strike-slip fault system, or a linked fault system controlled the basin by dominant extension and weak strike-slip and created fan-shaped depocenters surrounded by the two faults. From Es¹ Member to Dongying (东营) Formation, two major depocenters controlled by two mixed normal and sinistral strike-slip fault systems are located on the Linque (林雀) and Caofeidian (曹妃甸) subsags. During deposition of the Guantao (馆陶)-Minghuazhen (明化镇) Formation, the Nanpu sag successively developed and significantly expanded.

Fluid Geochemical Features and Preservation Conditions of Marine Stratum in Typical Structure of Jianghan Plain Area

Guosheng Xu, Deyu Gong, Haifeng Yuan, Changhong Li, Guozhi Wang, Xiaofeng Hu, Juanhua Lin, Jianmin Zhu

2011, 22(6): 768-779. doi: 10.1007/s12583-011-0226-1

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Abstract:
Many scholars carried out large quantity of researches on oil and gas preservative conditions of marine carbonate rocks from the aspects of cap rocks, faults, formation water, hydrodynamic, and tectonism. This article gives dynamic evaluation on oil and gas preservative conditions of marine stratum in Jianghan (江汉) plain of multiphase tectonic disturbance from the view of paleofluid geochemistry. The conclusion shows that there mainly existed fluid filling of two periods in the reservoir of Lower-Middle Triassic to Permian. The fluid filled in the earlier period came from Lower Palaeozoic. The interchange of fluid in Lower-Middle Triassic to Permian suggested the oil and gas in Lower Palaeozoic had been broken up. The fluid filled in the later period (Lower-Middle Triassic to Permian) came from the same or adjacent strata and lacked anatectic fluidogenous features coming from Palaeozoic. With good preservative conditions of bulk fluid at the time, the fluid of Lower-Middle Triassic to Permian and that of Lower Palaeozoic did not connect with each other. However, the hydrocarbon generation peak of marine source rocks had passed or the paleo-oil and gas reservoirs had been destroyed at that time and the marine stratum of Palaeozoic to Triassic in the research area did not put out commercial oil and gas flow.

Runoff Variation Law and Its Response to Climate Change in the Headstream Area of the Keriya River Basin, Xinjiang

Hongbo Ling, Qingqing Zhang, Wei Shi, Hailiang Xu

2011, 22(6): 780-791. doi: 10.1007/s12583-011-0227-0

[Abstract](979) [FullText HTML] (97) [PDF 534KB](21)

Abstract:
Based on the runoff and meteorological data of Langan (兰干) Hydrological Station from 1957 to 2009 in Keriya (克里雅) River, the periodicities, abrupt changes, and trends of climate factors and runoff were investigated by wavelet analysis and nonparametric test; then, the future change of the annual runoff was predicted by a periodic trend superposition model. In succession, the influencing volumes of climate change on the annual runoff were separated from the observation values of the annual runoff in Keriya River. The results show that (1) temperature series increased significantly, while the annual runoff and precipitation of Keriya River increased insignificantly at the significant level of α=0.05; (2) the common periods of 9 and 15 years existed in the annual runoff evolution process, and the primary periods of temperature and precipitation were 9 and 22 years and 9 and 13 years, respectively; (3) the annual runoff did not vary simultaneously with the abrupt change of climate factors in the headstream; the abrupt points of annual runoff and temperature are at 1998 and 1980 year, and that of precipitation is not so significant; and (4) the annual runoff will experience a decrease trend in the future period; the total increasing volume owing to climate change is 23.154×10⁸ m³ in the headstream during the period of 1999–2009; however, the stream flow has been nearly utilized completely due to the human activities in the mainstream area of Keriya River.

Precipitation Effects on Temperature—A Case Study in China

Aigang Lu

2011, 22(6): 792-798. doi: 10.1007/s12583-011-0228-z

[Abstract](987) [FullText HTML] (95) [PDF 559KB](23)

Abstract:
To discover the mechanism of the continuous summer temperature decline in certain regions against significant global warming, 456 national meteorological observational stations with long term of observed daily temperature and precipitation data were applied to analyze the relationship between precipitation and temperature. Results show that there is a significant negative correlation between precipitation and temperature, indicating that precipitation influences temperature significantly: the more the precipitation, the lower the temperature, and vice versa. The precipitation effect on temperature can reasonably interpret the typical summer temperature in Southwest China and can partly explain why global warming is more significant in winter than in summer and more significant in higher latitude areas than in lower latitude.

2011 Vol. 22, No. 6

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