1 Introduction

Mid Ocean Ridge Basalts (MORBs) with a large compositional variation were obtained along East Pacific Rise(EPR) (Zindler and Hart, 1986; Hanan and Schilling,1989; Bach et al., 1994; Niu et al., 1996; Regelous et al.,1999; Zhang et al., 2013). Most MORBs were found to be Normal Mid Ocean Ridge Basalts (N-MORBs); however,enriched samples were collected along ridges, and the fractional crystallization, partial melting degree, and mantle heterogeneity of these samples has led to a wide range of variation in their incompatible element concentrations and isotopic ratios (Bach et al., 1994; Niu et al.,1996; Regelous et al., 1999; Moreira et al., 2008). It is also considered that in seamounts or triple junction areas,the influence of ‘plume’ materials could be another reasonable explanation for this diversity (Haase et al., 1996;Niu et al., 1996; Haase et al., 1997; Kruz and Geist, 1999;Kruz et al., 2009).

Former research on EPR MORBs has shown they have very complex compositional variations. For example, for seamount basalts and MORBS at EPR 18˚–19˚S, Niu et al.(1996) proposed two independent processes: plume-like material invasion and low-degree melting, respectively.On Easter Island, Haase (2002) distinguished four end members for MORBs around the micro-plate, and suggested two different mixing processes for East Rift MORBs and West Rift MORBs, respectively. The author believed that East Rift MORBs were formed by mixing between a depleted upper mantle source and an enriched hotspot source, while the formation of the West Rift MORBs had no connection with hotpot contamination.However, in most cases, factors such as magma mixing and mantle heterogeneity are both considered to play important roles, especially in tectonic transition settings. Most of the geochemical research conducted at the Galápagos Triple Junction has focused on the Cocos-Nazca Ridges,while magmatism of the other two axes has rarely been discussed.

This paper therefore introduces geochemical and radio-isotopic analyses of MORBs from EPR 1˚–2˚S, where the diagenesis and source characteristics are introduced and discussed to provide a better understanding of magmatism under the Galápagos Triple Junction.

2 Geological Settings

The Galápagos Triple Junction (GTJ) is situated midway along the EPR where the Pacific, Nazca, and Cocos plates meet. Since a U.S. Navy survey confirmed it to be an ‘R-R-R’ triple junction (Johnson et al., 1976), exten-sive research has been conducted on the associated geometry, geophysics, and geochemistry, which has provided a considerable amount of valuable information.

For most triple junctions on the EPR, micro-plate formation is accompanied by plume (or hotspot) activities(Goldstein et al., 1991; Farley et al., 1993; Haase, 2002).However, the nearest hotspot to the GTJ is located under the Galápagos Archipelago on the Cocos-Nazca spreading center, which is more than 1000 km away from EPR ridges.On the basis of geochemical research on MORBs along the Cocos-Nazca ridge, the influence of the Galápagos hotspot has been restricted to a position east of 95.5˚W(Eason and Sinton, 2006), which is distant from the EPR ridges. Therefore, to gain a better understanding of the characteristics of MORBs around the GTJ, research on MORBs from EPR 1˚–2˚S are presented in this paper.

3 Sampling and Analytical Methods

本文利用国家统计局、各省 （市、自治区）（以下简称 “省份”）《统计年鉴》、2017年各省国民经济和社会发展统计公报、中国经济与社会发展统计数据库、 《中国国内生产总值核算历史资料：1952～1995》和 《中国国内生产总值核算历史资料：1996～2002》构建本文所需要的数据集。数据集包括1978～2017年中国各省份地区生产总值、就业人员数、固定资本形成总额，以就业人数代表各地区劳动力投入量，利用固定资本形成总额计算得到各地区各年度资本存量作为资本投入数据，同时以1978年作为研究基期，利用相关价格指数进行数据平减。

Fig.1 Bathymetric map for Galápagos Triple Junction and sampling location.

Table 1 Sample locations for MORBs from EPR 1˚–2˚S(‘Glass’ indicates glassy samples)

Sample Lithology Water depth(m) Longitude Latitude TVG02-1 Basalt(Glass) 1611 101.50˚W 1.22˚S TVG02-2 Basalt(Glass) 1611 101.50˚W 1.22˚S TVG06 Basalt 2869 102.29˚W 1.74˚S TVG07 Basalt 2872 102.28˚W 1.69˚S TVG10 Basalt 2915 102.26˚W 1.61˚S TVG11 Basalt 2826 102.18˚W 1.04˚S

However, the different mixing processes between Rb/Zr and (La/Sm)N do not suggest so (Fig.8). Sample 07 is the most primitive sample and has the lowest Rb/Zr and(La/Sm)N. Although all samples show positive correlations with respect to ratios, four of the enriched samples fall into two linear trends with high correlations (R2 ＞0.9), respectively; these different trends are also observed in the variation between Rb/Sr and 87Sr/86Sr (Fig.9).Samples 02, 07 and 10 locate on the similar linear trend,while samples 06 and 11 display obvious higher values of Rb/Sr. Certain differences exist between samples 06 and 11, and there are evident differences between the linear trends of these two.

On the basis of the above analysis, the samples presented in this study are found to have a very wide range of variation range in their incompatible element concentrations. The enriched sample (06) has high concentrations of certain highly incompatible elements (Rb, Ba, Nb,Ta, etc.); these values are similar to those of some typical E-MORBs. In addition, it has high ratios of some highly incompatible to less incompatible elements (K/Ti, Rb/Sr,Nb/Zr and Nd/Sm), and shows slightly lower values of(La/Sm)N, Nb/Zr and Rb/Sr for a given K/Ti. Therefore,sample 06 (and 11) shows a compositional similarity to other enriched samples from EPR 10˚N–10˚S, GSC, and the near-ridge seamount (Fig.4).

既然如此，纪实性为导向的新闻述本与虚构性为导向的“新闻电影”之述本都是“片面化的再现”，二者区别何在呢？区别就在于，新闻文本作为纪实型叙述，从底本的可能世界到述本的实在世界是一种直接指涉的再现关系。而电影文本作为虚构型叙述，从底本的可能世界到述本的“三界”混合则是“再现之再现”。这种“再现之再现”由于通达关系数量相对纪实型叙述要少得多，从而可能导致底本与述本之间的“模糊化”和“错位”。

Thirteen samples (four from 02, two from 06, three from 07, two from 10, and two from 11) were selected for major element analysis, which was conducted by X-ray fluorescence spectrometry (XRF) on fused-glass disks using a Shimadzu XRF-1500 at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Precision was ±1.3% relative to elements present in concentrations＞1.0 wt%, and about ±10% relative to elements present in concentrations ＜1.0 wt%.

Trace element concentrations (including rare earth elements) were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) at the Institute of Oceanology,Chinese Academy of Sciences. Sample powders were weighed to exactly 40 mg and transferred into Teflon beakers; 1.5 mL HF and 0.5 mL HNO3 were then sequentially added and samples were heated to 150℃ for 24 h on an electro-thermal plate. The temperature was subsequently lowered to 120℃, and 0.2 mL HClO4 was added.When white smoke had disappeared, 1 mL HNO3 and 1 mL H2O were added to the residues. Samples were then sealed and heated at 120℃ for 12 h. Dissolved samples were diluted 1000 times using 2% distilled super pure HNO3, and solutions were finally analyzed using Re as the internal standard (all contained RSD ＜ 4%).

Twelve samples (four from 02, two from 06, four from 07, one from 10, and one from 11) were selected for Sr,Nd, and Pb isotopic analysis via thermal ionization mass spectrometry (MAT261) at the Wuhan Center of Geological Survey, Ministry of Land and Resources of the People’s Republic of China. Samples were dissolved in a mixed acid of 2 mL HF and 0.2 mL HClO4 on a hotplate at 120℃ for over one week. After samples had been completely dissolved, the solutions were dried on a hotplate at 130–180℃ to remove HF and HClO4. Subsequently,sample residues were re-dissolved in 4 mL of 6 mol L−1 HCl and then dried again. Finally, samples were dissolved in 5 mL of 3 mol L−1 HCl prior to analysis.

临床中胆结石患者接受腹腔镜手术切除治疗是主要的方式,可是腹腔镜胆囊切除手术需要使用科学的麻醉方式,短时间确保麻醉的有效性和成功率,最大程度确保患者的麻醉效果。让手术顺利进行。腹腔镜胆囊切除手术使用的麻醉方式和手术的结果之间关联性紧密,根据临床研究显示,不科学的麻醉方式会让手术效果不佳,需要再次手术治疗,对患者的生命安全产生了很大的威胁,降低了医疗服务质量。所以,此次研究中,腹腔镜胆囊切除手术需要使用硬膜外麻醉,我们对研究进行了以下报道。

4 Results

In contrast, sample 07 is the most primitive sample and has the most ‘depleted’ chemical composition. It follows an N-MORB pattern, with low concentrations of these highly incompatible elements and very low ratios between them. More importantly, it has high values of 143Nd/144Nd(0.513234–0.513271) and low 87Sr/86Sr, which suggests it is more depleted than MORBs at EPR 10˚N–10˚S and the near-ridge seamount. In fact, the 87Sr/86Sr value of sample 07-3 (0.70213) is lower than that of MORBs previously reported, or of seamount samples from EPR, and is only comparable with some very depleted samples from the seamount (Sample 1158-2014, Fornari et al., 1988) or with those from very unusual tectonic settings (Samples GN 13-1 and GN 15-1, Wendt et al., 1999).

With reference to the analysis and comparison presented above, the isotopic ratios of MORBs from EPR 1˚–2˚S have a wide variation range. Sample 07 has very depleted isotopic ratios; other samples (02, 06, 10 and 11)show similarities and overlap the variation range of some typical N-MORBs from adjacent segments of the EPR axis. This difference cannot be explained simply by a petrologic process, but suggests the participation of at least two melts with different compositions.

Fig.2 Major element diagram for MORBs from EPR 1˚–2˚S (EPR MORB are samples from EPR 10˚N–10˚S collected from PetDB).

Compared with MORBs from EPR 10˚N–10˚S (Bach et al., 1994; Goss et al., 2010; Sims et al., 2002), our samples contain higher amounts of Al2O3 and Na2O, but slightly lower amounts of TiO2 and P2O5. Sample 07 shows extremely high values of Al2O3 and lower TiO2,while samples 06 and 11 have higher K2O than most EPR MORBs. In general, most of the major elements (Al2O3,TiO2, CaO, Na2O and P2O5) in our samples show welldefined trends for MgO (Fig.2), which suggests shallow-level differentiation from a similar magma source.Al2O3 and CaO have a negative correlation with MgO when its values are higher than 7.89 wt% (sample 07),which indicates the crystallization of olivine; however,they have a positive correlation with MgO values lower than 7.89 wt%, indicating the crystallization of plagioclase (or clinopyroxene).

The trace element concentrations of EPR 1˚–2˚S MORBs are listed in Appendix B, where it is evident that our samples also have a wide range of trace element concentrations. Fig.3 shows the E-MORB (Enriched Mid Ocean Ridge Basalt) pattern of sample 06, which has the highest concentration of some highly incompatible elements such as Rb, Ba, Nb, and Ta. For example, it has Nb concentrations of (10.8–11.1)×10−6, compared to 4.06×10−6 and 5.97×10−6 (on average) from EPR 10˚N–10˚S and the Galápagos Spreading Center (GSC), respectively. In contrast, Sample 07 has very low concentrations of these incompatible elements, similar to the amounts in some typical N-MORBs on the EPR. Other samples (02, 10 and 11)show a transitional pattern between samples 06 and 07.

Fig.3 Primitive mantle normalized abundance patterns to highly incompatible elements for basalts at EPR 1˚–2˚S(normalized value and E-MORB and N-MORB value are from Sun and McDonough, 1989).

The Sr, Nd and Pb isotopic compositions of our MORBs are listed in Appendix C. The most depleted sample(07) has extremely low 87Sr/86Sr (0.70213–0.702283) and 206Pb/204Pb (17.9532) but very high 143Nd/144Nd (0.513234–0.513289); these values are only comparable with those of some very depleted basalts on the EPR or of other basalts in some unusual tectonic settings (Regelous et al.,1999; Wendt et al., 1999). However, the enriched sample(06) is not as enriched as the incompatible element concentrations suggest. For example, its value of 87Sr/86Sr is only 0.70257–0.702664, which is only a medium value of MORBs from the EPR. In addition to sample 06, sample 11 has the highest values of 87Sr/86Sr (0.70268). The 206Pb/204Pb of sample 06 is only 18.2066, which is lower than that of sample 02 (18.5064).

5 Discussion

5.1 Comparison with Other Basaltic Samples from the EPR

以不同农林复合经营模式的各因素数据为依据，采取灰色关联分析法对不同农林复合经营模式的综合效益进行评价分析。具体分析步骤如下[11-12]。

Six blocks of basalts were obtained from five sites along the mid ocean ridge between 1˚S and 2˚S (Fig.1).Samples 06, 07, 10 and 11 were collected at a depth of over 2800 m beside the ridge, while sample 02 was obtained from a nearby seamount at a depth of 1611 m (Table 1). Sample 02 is glassy and the other samples have better crystallization. Observation with polarized-light microscope (POM) shows that plagioclase and olivine with automorphic and partial automorphic exist in most samples, and no sample exhibits weathering or alteration.

However with respect to the values of 87Sr/86Sr versus143Nd/144Nd, sample 06 is not considered to be ‘enriched’,as its incompatible elements concentrations suggest.Compared with E-MORBs from an adjacent area (Fig.5),sample 06 has medium values of 87Sr/86Sr (0.70257–0.702664), and evidently higher 143Nd/144Nd values than E-MORBs from the near-ridge seamount (0.7026–0.7030),in addition to E-MORBs affected by the Galápagos hotspot along GSC (0.7028–0.7032). This phenomenon is observed in Figs.6 and 7. Sample 06 has medium 206Pb/204Pb (18.2066) values compared to samples 02 and 07,which is similar to N-MORBS at EPR 10˚N–10˚S but lower than most GSC E-MORBs (about 19.0).

MORBs from the EPR 1˚–2˚S have a wide compositional range of major element concentrations (Appendix A). Values of Mg# [Mg/(Mg+Fe2+)] in samples vary from 41.11 to 54.74. Sample 07 is the most primitive sample with the highest value of MgO (7.80–8.61 wt%) and Mg#(53.32–54.74), and it also contains the highest amount of Al2O3 (16.9–17.14 wt%), which is higher than most EPR MORBs in 10˚N–10˚S (Fig.2). Conversely, Sample 06 is characterized by lower values of MgO (6.94–6.98 wt%)and higher concentrations of elements (K2O 0.39–0.38 wt%,P2O5 0.1851–0.1857 wt%), which are incompatible with mantle melting. With its higher values of K/Ti (0.34–0.35),sample 06 represents the most enriched sample in our research. The values of other samples (02, 10 and 11) represent a transition between samples 06 and 07.

In general, MORBs at EPR 1˚–2˚S can be divided into two types: 1) The first type comprises sample 07, which is representative of a typical N-MORB. Its low concentrations of incompatible elements and isotopic Sr and Pb suggest a very depleted source; 2) The second type comprises the other samples (02, 06, 10 and 11), and represents the transitional chemistry between an N-MORB and E-MORB. Although they contain relatively high concentrations of incompatible elements at different levels, they are not enriched by their isotopic ratios.

5.2 Petrogenesis and Source Characteristics of MORBs from EPR 1˚–2˚S

教师需对各类文学理论、文化史、作者生平和时代背景、文化语境等方面了然于胸。为学生构建大体文学史框架，让学生能对各时期文学、文化状况大体了解，以便对课外读物风格主旨的把握，注重文本分析的训练。朱光潜说“非这样锱铢必较不可”“一字不肯放松”的谨严和执着，就如“猛将用兵、酷吏治狱”；孙绍振教授对文本深层结构的解读；陈日亮老先生对各篇文章字词句段篇的分析。我们首先是读者，对文字和篇章结构敏感。

The most primitive sample, sample 07, suggests the participation of an extremely depleted melt with very high 143Nd/144Nd and low 87Sr/86Sr, whereas it is considered that other samples may have crystallized from a relatively enriched source. As all samples show good correlation on a major elements diagram (Fig.2) and with respect to incompatible elements ratios (Fig.4), it appears that they could have formed by a mixing between these two melts.

Fig.4 (La/Sm)N, Nb/Zr, Rb/Sr and Nd/Sm versus K/Ti for basalts at EPR 1˚–2˚S (EPR MORB are samples from EPR 10˚N–10˚S collected from PetDB; GSC are samples from Galápagos Spreading Center from PetDB).

Fig.5 87Sr/86Sr versus143Nd/144Nd compositions of basalts from EPR 1˚–2˚S (EPR MORBs are samples from EPR 10˚N–10˚S collected from PetDB; Garrett are samples from Garrett Transform in Wendt et al., 1999; and Seamount are samples from the near-seamount in Niu et al., 2002).

Fig.6 87Sr/86Sr versus206Pb/204Pb compositions of basalts from EPR 1˚–2˚S.

Fresh samples without alteration were chosen and ultrasonically cleaned in distilled water for 60 min (water was changed every 15 min) prior to drying in an oven at 60℃ . Samples were then crushed into ＜ 200 mesh particles before analysis.

Fig.7 143Nd/144Nd versus206Pb/204Pb compositions of basalts from EPR 1˚–2˚S.

Fig.8 Rb/Zr versus (La/Sm)N for MORBs at EPR 1˚–2˚S.

Fig.9 Rb/Sr versus87Sr/86Sr for MORBs at EPR 1˚–2˚S.

In both figures, samples 06 and 11 are seen to have higher values of Rb/Zr and Rb/Sr than other samples for given values of (La/Sm)N and 87Sr/86Sr, respectively. This phenomenon cannot be explained merely by the mixing between one depleted melt and one enriched melt. It is thus suggested the participation of two relatively enriched melts and one depleted melt. These two enriched melts have similar 87Sr/86Sr (0.70244–0.70268), 143Nd/144Nd(0.513086–0.513200), but a wide range of variation in their incompatible element concentrations. In addition, it is also of note our most depleted sample (07) and enriched sample (06) were sampled in two locations that were reasonably close to each other (about 5.6 km) and at a similar depth (2869–2872 m).

MORBs with limited isotopic ratios but variable incompatible elements concentrations have been mentioned and discussed in many previous papers (Plank and Langmuir, 1992; Frey et al., 1993; Niu et al., 1996), and mantle heterogeneity, magma mixing, and crustal contamination have all been presented as suitable explanations for this phenomenon. In this research, we propose a mixing in the source region by an intrusive melt in the form of veins or dykes; this melt was most likely a low- fugacity melt, as mentioned in Niu et al., (1996). Some samples(02, 10) represent the mixture of melts derived from different extents of melting, while sample (07) inherits its compositional characteristics from its depleted (or enriched) source with minor amounts of the mixing process.This explains the coexistence of some depleted MORBs(07) and enriched MORBs (06 and 10) (Fig.1). However,the formation of samples 06 and 11 is complicated, and it is considered that they may have formed via a process similar to that of samples 02 and 10, or that they simply display similar source characteristics to sample 07. It is thus considered that further analysis and discussion needs to be conducted in this region to provide more conclusive results.

6 Conclusions

1) EPR 1˚–2˚S MORBs can be divided into two types.Sample 07 represents a N-MORB type with a low concentration of incompatible elements but very high 144Nd/143Nd and low 87Sr/86Sr and 206Pb/204Pb. However, samples 02, 06, 10, and 11 have high concentrations of incompatible elements at different levels, but medium isotopic ratios for Sr, Nd and Pb, and are thus similar to typical N-MORBs on the EPR.

2) We propose that at least three endmembers contribute to the magmatism under ridges at EPR 1˚–2˚S. The depleted one has very high values of 144Nd/143Nd and low 87Sr/86Sr and 206Pb/204Pb, while the two enriched endmembers have similar isotopic ratios but variable concentrations of incompatible elements.

为保证臭气得到有效收集，必须分别对渗沥液一、二期A/O系统的O池等进行密封加盖，密封方式根据现场各臭气源的构筑物构造特点来确定。充分考虑防腐性能、盖板形式、投资成本、使用寿命等因素。

3) We also propose that samples 02 and 10 are formed by the mixing of two sources that have different chemical compositions, while sample 07 crystallized from its very depleted source without undergoing a mixing process.However, samples 06 and 11 have a very different formation, and further research is required to determine their genesis.

本研究发现是否患有慢性病、睡眠质量、性别以及近 2 周内有无身体不适是 SF-36 量表各维度得分的主要影响因素，女性、睡眠质量高、无慢性病、近 2 周内无身体不适者健康生命质量更高，其他因素无明显影响。说明提高睡眠质量、控制慢性病、减少短期内身体不适等有助于提高该特殊人群的健康生命质量。

Acknowledgements

We would like to thank the crew of the DY105-12 and 14 for their assistance in collecting samples, and for anonymous reviewers for their suggestions. This study was supported by the Special and Frontier Foundation for the Twelve Five Plan of the China Ocean Mineral Resources Research and Development Association (Nos.DY125-22-QY-21 and DY125-12-R-02).

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