Geochemical characteristics of fault core and damage zones of the Hong-Che Fault Zone of the Junggar Basin (NW China) with implications for the fault sealing process

Accepted Manuscript Geochemical characteristics of fault core and damage zones of the Hong-Che Fault Zone of the Junggar Basin (NW China) with implications for the fault sealing process Yin Liu, Kongyou Wu, Xi Wang, Yangwen Pei, Bo Liu, Jianxun Guo PII: DOI: Reference:

S1367-9120(17)30204-3 http://dx.doi.org/10.1016/j.jseaes.2017.04.025 JAES 3061

To appear in:

Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

11 November 2016 21 April 2017 22 April 2017

Please cite this article as: Liu, Y., Wu, K., Wang, X., Pei, Y., Liu, B., Guo, J., Geochemical characteristics of fault core and damage zones of the Hong-Che Fault Zone of the Junggar Basin (NW China) with implications for the fault sealing process, Journal of Asian Earth Sciences (2017), doi: http://dx.doi.org/10.1016/j.jseaes.2017.04.025

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Geochemical characteristics of fault core and damage zones of the Hong-Che Fault Zone of the Junggar Basin (NW China) with implications for the fault sealing process

Yin Liu*, Kongyou Wu*, Xi Wang, Yangwen Pei, Bo Liu, Jianxun Guo School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China

Manuscript submitted to Journal of Asian Earth Sciences

*

Corresponding author: Dr. Yin Liu. Dr. Kongyou Wu E–mail: [email protected]; [email protected] Tel: +86-183 6626 6387

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Abstract Faults may have a complex internal structure, including fault core and damage zone, and can act as major conduits for fluid migration. The migration of fluids along faults is generally associated with strong fluid–rock interaction, forming large amounts of cement that fill in the fractures. The cementation of the fault fractures is considered to be one of the important parameters of fault sealing. The different components of faults have diverse geochemical features because of varying physical characteristics. The investigation of the geochemical characteristics of the fault and damage zones could provide important information about the fault sealing process, which is very important in oil and gas exploration. To understand the fault-cemented sealing process, detailed geochemical studies were conducted on the fault and damage zones of the Hong-Che Fault of the northwestern Junggar Basin in China. The major and trace element data of our study suggest that the fault core is characterized by higher loss on ignition (LOI), potassium loss, Chemical Index of Alteration (CIA), and Plagioclase Index of Alteration (PIA) values and lower high field strength element (HFSE), large-ion lithosphile element (LILE), and rare earth element (REE) concentrations compared with the damage zone, implying more serious elemental loss and weathering of the fault core compared with the damage zone during faulting. The carbon and oxygen isotope data reveal that the cement of the Hong-Che Fault Zone formed due to multiple sources of fluids. The fault core was mainly affected by deep sources of hydrothermal fluids. In combination with previous studies, we suggest a

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potential fault-cemented sealing process during the period of fault movement. The fault core acts as the fluid conduit during faulting. After faulting, the fault core is cemented and the damage zone becomes the major conduit for fluid migration. The cementation firstly occurs on two sides of the damage zone in the upper part of the fault based on permeability and geochemical studies and then expands to the whole fault. This process explains the relationship between the fault-cemented sealing and oil and gas accumulation.

Keywords: Fault zone architecture; Junggar Basin; Hong-Che Fault Zone; Geochemical characteristics

1. Introduction It is widely accepted that the fault can act as conduit, barrier, or combined conduit–barrier structure for hydrocarbon migration (Hooper, 1991; Cao et al., 2010; Matonti et al., 2012; Walker et al., 2013), which plays an important role in petroleum exploration. Researchers suggest that faults have a complex internal structure, which can be divided into two components, fault core and damage zone (Sibson, 1977; Chester and Logan, 1986; Caine et al., 1996; Heynekamp et al., 1999; Hesthammer et al., 2000; Faulkner et al., 2003; Kim et al., 2004; Brogi, 2008; Faulkner et al., 2010; Michie et al., 2014; Bauer et al., 2015). The fault core is composed of unconsolidated fault gouge, breccia, and geochemically altered fault rocks (Sibson, 1977; Loveless et

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al., 2011). The damage zone is characterized by multiple subsidiary fractures, which does not change the lithology of the rocks (Chester and Logan, 1986; Antonellini and Aydin, 1994; Caine et al., 1996). The uncemented fractures in the damage zone are the main paths for fluid migration (Gibson, 1998; Faulkner et al., 2010; Sutherland et al., 2012). The different components of the fault zone have distinct physical characteristics; the density and permeability of the fault core are significantly lower than that of the damage zone during the rest time (Antonellini and Aydin, 1994; Caine et al., 1996; Gibson, 1998; Faulkner et al., 2010). Five types of fault seal processes have been identified including clay smearing, cementation of fractures, cataclasis, diffusive mass transfer, and porosity reduction by disaggregation and mixing (Knipe, 1992,1997; Knipe et al., 1997; Fisher and Knipe, 1998; Fisher et al., 2003; Pei et al., 2015). Much attention has been paid to the cementation of fractures; a lot of work has been carried out on this topic (Knipe et al., 1998; Wu et al., 2011; Wu et al., 2012). Although researchers noticed that the cementation increases the capacity of fault sealing, several characteristics, such as the fault sealing process, cement source, and relationship between the hydrothermal fluids and petroleum migration, are still discussed. In fact, hydrothermal fluids are extremely active in the fault zone, usually associated with strong fluid–rock interaction (Aydin, 2000; Boles and Grivetti, 2000; Gudmundsson et al., 2001; Fisher et al., 2003; Barker et al., 2009; Molli et al., 2010). The activities of fluids along the fault zone are generally associated with the migration and isotopic fractionation of multiple elements (Yang and Zhang, 1996;

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Molli et al., 2010; Kim et al., 2012; Liu et al., 2015). Multiple filled veins in the fault zone are geological proof of hydrothermal fluid activity. Multiple fault activities generate a complex network of fractures, which is filled by veins (Hooper, 1991; Lu et al., 2004). Some studies suggested that the fault seal capacity is highly related to the filled fractures in the damage zone (Gibson, 1994). Geochemical and isotopic studies demonstrated that the sources of hydrothermal fluids are very complex and include magmatic, metamorphic, formation, meteoric, and deep earth water (Sample et al., 1993; Liu and Liu et al., 1997; Liu et al., 2004; Cao et al, 2007; Becken et al., 2011). The physical deformation of strata or rock due to structural stress can change the physical-chemical environment (Lv et al., 2011), causing the precipitation of minerals. Therefore, detailed studies on the geochemical characteristics of the different components of fault zones will help to distinguish the distinct nature and sources of hydrothermal fluids and to investigate the fault seal process and fault development. We chose the Hong-Che Fault Zone at the western margin of the Junggar Basin as an example. The Junggar Basin is the second largest petroliferous basin in China. The third-round of resource assessment showed that the total oil and gas resources of this basin reach 106.8 × 108 t including 20.9 × 108 t crude oil and 85.9 × 108 t natural gas (He et al., 2004; Li, 2005). The western margin of the Junggar Basin is the most important oil and gas accumulation area. Petroleum exploration testified that most of the oil and gas reservoirs are distributed along the faults in plane and vertical profiles

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(He et al., 2004; Xin et al., 2006; Cao et al., 2010), reflecting the effects of the faults on the hydrocarbon accumulation. The systematic evaluation of the fault seal capacity in this area is therefore important for petroleum exploration. In this paper, we carried out mineralogical and geochemical analyses on different components of the fault zone structure of the Hong-Che Fault Zone. Our new data provide new insights into the fault sealing process in the fault zone.

2. Geological Setting The Junggar Basin is located in the western part of the famous Central Asian Orogenic Belt (CAOB; Figure 1a; Sengor et al., 1993; Windley et al., 2007; Kröner et al., 2008). Several large orogenic belts surround the basin including the Altai–Kelameili Mountains to the north, Zaire-Hala’alate Mountains at the northwestern margin, and Yilinheibiergen–Bogda Mountains to the south (Figure 1b). Geophysical data revealed that the Junggar Basin is a complex composite basin, which endured polycyclic tectonic events (Feng et al., 1989; Carroll et al., 1990; Allen et al., 1995; Chen et al., 2002; Wu et al., 2005). The formation and tectonic evolution of the Junggar Basin is still debated; however, most studies suggest that the basin formed in the Late Carboniferous due to the collision and amalgamation of the CAOB (Carroll et al., 1990; Allen and Vincent, 1997; Wu et al., 2005; Chen et al., 2005). The Junggar Basin entered an intracontinental depression development stage in the Mesozoic due to compression from the northwest and northeast (Sengör, 1990;

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Wu et al., 2005; Cao et al., 2010), forming and reactivating the internal structure of the basin (Allen and Vincent, 1997; Wu et al., 2013; Yu et al., 2016). The reverse boundary faults of the Junggar Basin gradually stopped to slip (Wu et al., 2005; Chen et al., 2005) from Late Jurassic to Early Neogene. The regional stress environment changed from compression to weak stretch, accompanied by the development of N–S-trending and E–W-trending normal faults. From the Neogene to Quaternary, a rejuvenated foreland basin developed in the Junggar Area due to the collision of the Indian Ocean and Eurasian Plates (Wu et al., 2005; Chen et al., 2005; Cao et al., 2005). Multiple phases of tectonic movement led to the development of a complex fault system. Thousands of faults developed in the Junggar Basin due to polycyclic tectonic movements. The Hong-Che Fault Zone is one of them. Tectonically, the Hong-Che Fault Zone is located at the western margin of the Junggar Basin. Geographically, it developed between Hongshanzui and Chepaizi in the Xinjiang Province. It is approximately 110 km long and comprises three major faults, the Hongche, Xiaoguai, and Cheqian faults, from east to west (Figure 1c), forming an imbricate fault system (Figure 2). To the deep, they merged into an uniform detachment surface (He et al., 2004). The strike of this fault zone is roughly N–S-trending, with an “S” shape in the plain view and dips to the west. It is connected to the Zaire Mountain to the north. The cross-sectional geometry of the fault planes is upper steep, lower gentle, and listric. The faults in the Hong-Che Area are generally interpreted as reverse faults and

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cut the strata from the Carboniferous to Upper Jurassic (He et al., 2004). Primary measurements suggested that the displacement of these faults varies from 520–1500 m (He et al., 2004). Based on the fault activity, this fault zone initially formed in the Late Carboniferous and continued to be active until the Early Jurassic, which means that it is a long-lived fault (Figure 2; He et al., 2004; Yan et al., 2008). Seismic data revealed that the major part of the Hong-Che Fault Zone developed in the Carboniferous (Figure 2), which is mainly composed of volcanic rocks including grey tuff, andesite, volcanic breccia, and basalt. The hanging wall consists of thin layers of Triassic and Jurassic deposits; Carboniferous deposits do not occur. The strata of the footwall are more complete and thicker than that of the hanging wall. Three large depressions surround the fault zone, the Mahu, Pen 1 Well West, and Shawan depressions, providing abundant sources of petroleum. The Permian to Quaternary strata comprise the major sedimentary sequence of this area, with a total thickness > 10 km. The stratigraphy and major lithology of the Hong-Che Fault Zone are summarized in Figure 3.

3. Samples and methods We divided the fault zone structure of different well cores based on previous studies of the lithological characteristics of the different components of the fault zone. To study the geochemical characteristics of the fault, 19 samples were collected from different components of the fault zone structure (Figure 4). All samples are from the

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Upper Carboniferous. The protoliths surrounding the fault zone are mainly andesite and andesitic tuff (Figure 4). A detailed description and the location of these samples are listed in Table 1. All samples were ground into thin sections and crushed into powder of less than 200-mesh size in an agate shatterbox. The major and trace elements of 16 samples from the fault zone were measured by ALS Chemex Co. Ltd, Guangzhou, China. The major elements were determined by X-ray fluorescence (XRF), with a precision greater than 5%. The trace element contents were determined using inductively coupled plasma-mass spectrometry (ICP-MS; Perkin Elmer Elan 9000), with a precision better than 10%. Eleven calcite vein samples from different components of the fault zone were selected for carbon and oxygen isotope analyses. The carbon and oxygen isotope analyses were conducted at the Key Laboratory of Nuclear Resources and Environment (Ministry of Education), East China Institute of Technology, using a Thermo Finnigan MAT 253 mass spectrometer. The calcite vein samples were handpicked (purity > 95%) and crushed into powder of less than 200-mesh size in an agate shatterbox. Before mass spectrometer analysis, all samples were treated in a thermostatic bath at 75 °C for one hour and reached equilibrium with phosphoric acid. The precision of δ13C and δ18O is ≤ 0.2‰. The carbon and oxygen isotope ratios were normalized on the Vienna Peedee Belemnite (VPDB) value using the international standard NBS-19 (δ13CVPDB = +1.95‰, δ18OVPDB = −2.20‰).

4. Results

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4.1. Petrological and microstructural characteristics of the fault zone Representative core samples from the Hong-Che Fault Zone were used in this study based on previous analyses of the physical characteristics of different components of the fault zone (Antonellini and Aydin, 1994; Caine et al., 1996; Gibson, 1998; Faulkner et al., 2010). Three types of fault core samples can be distinguished including relatively unconsolidated fault breccia (Figure 5A), cemented cataclasite (Figure 5B), and altered cataclasite (Figure 5C). The unconsolidated fault breccia is mainly composed of 0.5–5-cm breccia from the wall rock. The breccia usually has bad psephicity with unconsolidated fault gouge filling. The cataclasite mainly comprises brittle clast fragments (< 2 cm) and gouge, with hydrothermal cementation filling fragments and fractures. Parts of the cataclasite of the Hong-Che Fault Zone were highly altered by hydrothermal fluids and multiple types of alteration minerals formed (Figure 5D-I). Strong fluid–rock reaction led to chlorite, serpentine, zeolite, illite, smectite, and sericite alteration of the fault rock minerals, with notable foliation due to the alignment of minerals (Figure 5C). The damage zone of the Hong-Che Fault developed multiple fractures, which were filled by hydrothermal calcite, quartz, zeolite, and serpentine (Figure 5D). Calcite is the major type of cementation in the fractures of the damage zone. Microscopic observations show that the reaction between the hydrothermal fluids and intermediate–basic volcanic rock caused carbonatization and zeolitization, which formed large amounts of calcite and zeolite veins (Figure 5E) in the fault zone. Silicification is uncommon in the Hong-Che Fault

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Zone; however, it can be easily recognized under the microscope based on filled fractures and tiny veins (Figure 5F). Feldspar, including plagioclase, albite, and K-feldspar, altered to chlorite, illite, and smectite due to hydrothermal fluids and filled in the cracks or obliterated the original texture of the grains (Figures 5G and 5H). Sericite, mainly due to the alteration of plagioclase and K-feldspar, can also be observed in this area, filling in along the cleavage and in the microfractures of the grains (Figure 5I). Parts of the primary minerals of the fault core were totally altered to chlorite and serpentine due to the extremely strong fluid–rock interactions. The crosscutting fractures indicate multiple phases of fault activities during the evolution of the fault (Figure 5J). The cataclasite thin sections of the fault core show brittle grain particles with small displacement (Figure 5K) or lithic fragments (Figure 5L) surrounded by fine-grained fragments, clay, and matrix (mainly smashed grains and cements). The total matrix can reach 40% to 70% based on microscopic estimates. Small fractures cutting or surrounding the grains are usually filled with calcite, zeolite, quartz, and clay veins (Figures 5K and L). Figure 5M shows large-scale serpentine-filled fractures, which were generated in the cataclasite of the Hong 63 well. The contact boundaries between the cataclasite area and serpentinization zone are clear; the fine-grained particles and matrix increased close to the boundaries.

4.2. Whole rock major and trace element geochemistry

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The chemical compositions of 16 samples from different components of the Hong-Che Fault Zone are listed in Tables 2 and 3. We selected eleven fault core samples and five damage zone samples for whole rock major and trace elemental analysis to compare the geochemical characteristics of different components of the fault zone. The geochemical contents of the fault core and damage zone vary (Figure 6). The major element contents are shown in Figure 6a. The SiO2 concentration of the fault core samples ranges from 21.48 to 65.25 wt.%, with an average of 51.65 wt.%. The Al2O3, Fe2O3T, K2O, MgO, Na2O, and TiO2 contents are 7.48–18.08 wt.%, 0.97–9.52 wt.%, 0.09–2.24 wt.%, 0.53–5.44 wt.%, 1.21–6.61 wt.%, and 0.11–0.86 wt.%, with average contents of 14.86 wt.%, 6.62 wt.%, 0.78 wt.%, 3.20 wt.%, 3.74 wt.%, and 0.68 wt.%, respectively. The CaO and LOI values vary strongly, ranging from 0.37 to 36.50 wt.% and 2.96 to 30.86 wt.%, respectively. Compared with the fault core, the damage zone samples have relatively higher SiO2 contents, ranging from 56.58 to 64.26 wt.%, with an average of 59.32 wt.%. The abundances of Al2O3, Na2O, and TiO2 of the damage zone are similar to those of the fault core; the contents range from 13.51–15.99 wt.%, 3.03–4.27 wt.%, and 0.60–0.85 wt.%, with the average values of 14.85 wt.%, 3.80 wt.%, and 0.72 wt.%, respectively. The Fe2O3T and MgO concentrations of the damage zone vary from 4.45–8.93 wt.% and 1.42–2.24 wt.%, with averages of 6.07 wt.% and 1.79 wt.%, respectively, and are slightly lower than those in the fault core. However, the K2O concentration in the damage zone is notably higher than that of the fault core; it varies from 1.02–3.16 wt.%, with an average of

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2.10 wt.%. The trace element concentrations are shown in Figure 6b. The Nb content of the fault core samples ranges from 0.7 to 5.5 ppm, with an average of 1.89 ppm; the Nb concentration of the damage zone samples varies from 2.8 to 8.4 ppm, with an average of 5.28 ppm. Most Ta contents of the fault core samples are below the detection limit; only three samples have a Ta content ranging from 0.1 to 0.3 ppm, with an average of 0.23 ppm. The Ta concentration in the damage zone ranges from 0.1 to 0.5 ppm, with an average of 0.28 ppm. The Hf concentration in the fault core varies from 0.7 to 3.9 ppm; the average value is 1.98. The Hf content of the damage zone ranges from 2.9 to 5.9 ppm, with an average of 4.18 ppm. The Y, Zr, Th, and U concentrations of the fault core range from 5.7 to 24.3 ppm, 26 to 137 ppm, 0.27 to 5.4 ppm, and 0.1 to 2.61 ppm, with average values of 16.69 ppm, 69.36 ppm, 1.52 ppm, and 0.60 ppm, respectively. The Y, Zr, Th, and U concentrations of the damage zone vary from 23.7 to 31.8 ppm, 104 to 220 ppm, 2.04 to 7 ppm, and 0.73 to 2.38 ppm, with averages of 28.82 ppm, 154.6 ppm, 4.03 ppm, and 1.35 ppm, respectively. The fault core samples generally show lower contents of high field strength elements (HFSEs) such as Nb, Ta, Hf, Y, Zr, Th, and U. The Rb, Ba, and Cs concentrations of the fault core range from 2.3 to 50.2 ppm, 17.9 to 777 ppm, and 0.09 to 2.41 ppm, with average contents of 16.74 ppm, 234.05 ppm, and 0.60 ppm, respectively. The Rb, Ba, and Cs contents of the damage zone vary from 22.5 to 86.4 ppm, 258 to 984 ppm, and 0.56 to 4.68 ppm, with average values of 46.62 ppm, 531.6 ppm, and 1.84 ppm,

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respectively. The results show that the average contents of some large-ion lithosphile elements (LILE), including Rb, Ba, and Cs, of the fault core are also lower than those of the damage zone. The fault core and damage zone are both characterized by pronounced negative Nb–Ta, Ti, and P anomalies and slightly weaker Zr anomalies in the primitive-mantle normalized spider diagram (Figure 7a). Most of the trace element contents of the damage zone are slightly higher than those of the fault core. The total rare earth element (REE) concentration of the fault core ranges from 20.9 ppm to 89.9 ppm, with an average of 51.2 ppm (Table 3). However, the total REE content of the damage zone varies from 83.9 ppm to 125.3 ppm (Table 3) and the average value is 106 ppm, which is much higher than that of the fault core. The δEu value of the fault core ranges from 0.82 to 1.19, showing inconspicuous negative or slightly positive anomalies (Table 3). The damage zone has slightly negative Eu anomalies; the δEu value ranges from 0.70 to 0.92, with an average of 0.83. No significant Ce anomalies have been observed in both the fault core and damage zone samples. The chondrite-normalized REE patterns of both the samples of the fault core and damage zone exhibit apparent fractionation of light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs; Figure 7b), with LaN/Yb N ratios varying between 1.9 and 5.1 and 2.81 and 5.84, respectively.

4.3. Carbon and Oxygen isotopes

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The major cementation in the Hong-Che Fault Zone is calcite, thus the calcite veins of six fault core samples and five damage zone samples were selected for carbon and oxygen isotopic analyses (Table 4). The δ13CVPDB values of fault core range from -18.4 to -7.1‰, with an average value of -12.9‰. The damage zone samples have δ13CVPDB values ranging from -10.3‰ to -6.6‰, and the average values is -8.94‰, which is slightly higher than that in the fault core. The oxygen isotope values display relatively coherent variations. The δ18OvSMOW values of fault core fluctuate from 2.7‰ to 14.0‰, with an average of 9.93‰. In the damage zone, the δ18OVSMOW values, which vary between 4.8‰ and 18.0‰ (the average is 14.52‰), are slightly higher than those in the fault core.

5. Discussions and implications 5.1. Geochemical characteristics and source of hydrothermal fluids in Hong-Che Fault Zone It is important to firstly identify useful geochemical signals and possible sources of hydrothermal fluids to discuss the geochemical processes of the fault zone. To investigate the significance of the difference in mean values between the geochemical data of fault core and damage zone, we use the Welch’s t-test in the case of heteroscedastic to examine the difference of mean values of the main major and trace elements (Table 5). The P (2-tailed) values suggest that the K2O, MgO, ZrO2, La, Ce, Nd, Rb, Th, Nb, Hf, Y and Zr has significance statistically difference (P<0.05) and

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support that the mean values of these elements in the fault core are quite different than the damage zone. However, the mean values of some elements and parameters, such as SiO2, CIA, PIA and Sr, show no statistically significant, though the mean value of these elements in the fault core are different from the damage zone. The t-test can reflect the statistically difference to some extent, but the test results would better not be used arbitrarily because they are affected by many factors, for example, the sample size. Low capacity of samples is likely to lead to the wrong judgment. Therefore, it would be better to consider the meaning of data themselves, and then supplement by the statistical methods. The high loss on ignition (LOI) can reflect the alteration of samples to some extent. The analyses results suggest that both the fault core and damage zone of the Hong-Che Fault have high LOI values ranging from 2.96 to 30.86 wt.% and 4.41 to 7.43 wt.%, respectively, implying that these samples may have been highly affected by hydrothermal fluids. Under the influence of hydrothermal fluids, some elements changed during the chemical process, especially mobile elements such as K, Rb, and Na (Pearce and Cann, 1973; Winchester and Floyd, 1977; Humphris and Thompson, 1978; Alderton et al., 1980; Kim et al., 2012; Walker et al., 2013; Frery et al., 2015). Different components of the fault zone have therefore distinct geochemical characteristics. Goddard and Evans (1995) argued that the fault core exhibits 0% to 60% volume loss of soluble elements, such as Si, K, Al, and Na, based on measurements against

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immobile Ti in the damage zone. Niwa et al. (2015) also suggested that there is a clear depletion in SiO2, Na2O, K2O, and all REE except Eu in the fault gouge. The fault core samples of the Hong-Che Fault Zone plot in a much wider area in the Zr/TiO2–SiO2 diagram (Figure 8A) than the damage zone samples and some specimens have extremely low silica contents, suggesting that the fault core might have endured a certain degree of silica loss. Among the major elements, strongly mobile potassium shows apparent differences in the various components of the fault zone. In the SiO2-K2O diagram (Figure 8B), both the fault core and damage zone samples have scattered data scope, however, most of the fault core samples show relatively lower content of SiO2 and K2O than the damage zone, suggesting the potassium in the fault zone endured alteration to some extent. This conclusion is also supported by the CaO + Na2O–Fe2O3T + MgO–K2O diagram (Figure 9A) in which most of the samples of the Hong-Che Fault show apparent trends of chloritization and sericitization; the fault core exhibits more serious potassium loss than the damage zone. Weathering is a complicated process that can transform volcanic glass and unstable minerals, such as feldspar and mica, into clay (McLennan et al., 1993). As mentioned above, the different components of the fault zone have distinct physical characteristics (Antonellini and Aydin, 1994; Caine et al., 1996; Gibson, 1998; Faulkner et al., 2010), which may cause the different fluid–rock characteristics and weathering degree of the fault core and damage zone. The Chemical Index of Alteration (CIA) is a parameter that can be used to identify the degree of weathering

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(Nesbitt and Young, 1982). The CIA values of the fault core samples of the Hong-Che Fault range from 45.65 to 71.54, with an average of 57.38, and are higher than those of the damage zone (47.30 to 55.89; average of 52.21; Table 2), implying that the weathering degree of the fault core is higher than the damage zone. This result is also notable in the A–CN–K diagram (Figure 9B); the fault core shows lower potassium values and a higher weathering degree than the damage zone. The Plagioclase Index of Alteration (PIA) is another parameter to quantify the degree of weathering (Fedo et al., 1995). The PIA values of the fault core samples of the Hong-Che Fault Zone (Table 2) range from 45.63 to 81.59, with an average of 60.42. The PIA values of the damage zone vary from 47.07 to 65.10 and the average value is 55.37. The fault core also has higher PIA values than the damage zone, supporting the fact that the fault core has a higher weathering degree than the damage zone. Zirconium is generally considered to be the most immobile element during lowto medium-grade metamorphism and severe hydrothermal alteration (Gibson et al., 1982). Therefore, La, Ce, Nd, Rb, Ba, Th, Nb, Cr, Cs, Hf, Sr, and Y were plotted against Zr to evaluate the effects of alteration on different components of the fault zone. The data suggest that most of the HFSEs, such as Nb and Hf, increase with increasing Zr, with limited scatter (Figure 10), indicating that they are immobile during alteration. However, the data also reflect that most of the HFSE and LILE concentrations of the fault core are relatively lower than those of the damage zone (Figures 6, 7, and 10), implying that the fault activities might lead to a notable loss of

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trace elements in the fault core. The REE content also supports this result. The damage zone has much higher REE concentrations than the fault core (Figure 7 and Table 3). Strontium is generally enriched in the hydrothermal fluids, especially in the low-temperature fluids (Yang et al., 2009). The analyses results reflect that the fault core has a much wider variety of Sr contents than the damage zone (Figure 6), implying that the fault core was also affected during fault deformation. Yttrium and holmium occur exclusively in the trivalent state in the hydrothermal systems and have very similar ionic radii (Shannon, 1976); thus, Y and Ho should behave coherently in geological environments (Bau and Dulski, 1995). Experimental studies demonstrated that neither partial melting nor fractional crystallization fractionate Y and Ho and the Y/Ho ratio roughly equals 28 based on the calculation of chondritic data (Anders and Grevesse, 1989). However, the hydrothermal fluid system will cause notable Y–Ho fractionation (Bau and Dulski, 1995; Bau et al., 1997). The data of the Hong-Che Fault Zone show that the damage zone has relatively stable Y/Ho values, ranging from 30.0 to 31, while the Y/Ho values of the fault core significantly vary from 28 to 32, implying that the hydrothermal fluids also influenced the fault core during the fault activity. According to the above-mentioned sample description, all samples were collected from the internal structure of the Hong-Che Fault Zone. Microscopic and hand specimen observation reflected that the lithologies of these samples are andesite, tuff and volcanic breccia (Figure 4, Figure 5I, K, L, M, Table 1). In the Nb/Y-Zr/TiO2

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diagram (Figure 11), most of the samples drop in the andesite, andesite/basalt area. Besides, the locations of these samples are near to each other and collect from the Upper Carboniferous. Therefore, they were derived from a same magmatic event. In this study, we found that the geochemical characteristics of the fault core and damage zone are always different, for example, the Zr and Hf anomalies in the spider diagram (Figure 7A). These differences cannot be explained by the magmatic evolution because the differentiations of chemical features caused by fractional crystallization are generally continuous instead of separating into two groups. It means that the chemical differences between the fault core and damage zone are due to they are in different components of fault zone architecture. Hydrothermal fluids and fault activities therefore mainly influence the geochemical characteristics that we compare in the above sections. Both the major and trace elements of the Hong-Che Fault Zone suggest that the fault core might have endured more serious elemental loss and more weathering than the damage zone; in addition, the hydrothermal fluids also affected the fault core during fault deformation. The source of the hydrothermal fluids is an important topic of the discussion of the formation of cementation in the fault zone; carbon and oxygen isotopes might provide a convincing explanation. Many researchers suggested that different sources of carbon and oxygen might have distinctive isotopic values. Hoefs (2008) indicated that there are mainly three sources of carbon in the hydrothermal system including (1) marine carbonate, which has δ18CVPDB values ranging from −4‰ to 4‰, with an

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average of ~0‰; (2) deep source carbon from mantle polyphaser system, with δ18CVPDB values ranging from −5‰ to −8‰; and (3) carbon in the sedimentary organic matter, with δ18CVPDB values generally lower than −20‰. Kaufman and Knoll (1995) argued that δ18OvPDB values < −5‰ and < −10‰ might represent slightly altered and highly altered carbonate samples. Our data reveal that the isotopic values of calcite veins in the fault core and damage zone of the Hong-Che Fault scatter in the δ18OVMOW–δ18CVPDB diagram (Figure 12) and have no typical values, implying that the multiple sources of hydrothermal fluids and both the fault core and damage zone were altered in this fault. This conclusion is also supported by core sample observations. In addition, our data also show that the fault core samples mainly plot near the area of original or deep sources; however, the damage zone plots in the mixed area of deep sources and sedimentary organic matter and marine carbonate sources. Meanwhile, one fault core and one damage zone sample plot close to the meteoric water line, implying that meteoric water might also contribute to the fault sealing in the Hong-Che Fault Zone. In addition, Hong-Che Fault is a deep root fault, which can cut through the strata and extend to the surface during faulting based on the seismic data, reflecting that the meteoric water could migrate along the fault and mix with the other source of hydrothermal fluids. To sum up, the fault core is mainly affected by deep sources of hydrothermal fluid; the damage zone is influenced by a mixture of multiple fluid sources, which might originate from the surrounding strata, deep mantle, and meteoric water. These results can be explained with the seismic

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pumping mechanism suggested in Sibson et al.(1975). The seismic pumping process will transport deep-source hydrothermal fluids mainly along the fault core during fault activity. Therefore, the fault core stores more deep-area information.

5.2. Fault sealing process and its implication for petroleum exploration Cementation is one of the most important factors affecting the fault sealing process (Gibson, 1994; Knipe et al., 1998; Boles and Grivetti, 2000; Faulkner et al., 2010; Wu et al., 2011; Matonti et al., 2012; Pei et al., 2015). As mentioned above, the Hong-Che Fault is a large fault that endured multiple phases of activity and became an important migration path connecting the surface and underground fluids. Petroleum exploration testified that the fault block is the main type of trap in the Hong-Che Fault Zone (Cao et al., 2005; Cao et al., 2010), which means that the fault sealing process is important for the accumulation of hydrocarbon. Our data reveal that the cementation in the Hong-Che Fault Zone is due to the mixture of different sources of fluid and the fault core endured more serious elemental loss and weathering than the damage zone. We also provide geochemical proof for the fact that the fault core is the major region of hydrothermal fluid migration during faulting. Previous studies also determined that the fault core has higher permeability during faulting; the damage zone has a much higher permeability than the fault core after faulting, making the damage zone a major region of fluid migration (Indrevær et al., 2014). In combination with these studies, we suggest the following fault sealing process, which

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is affected by cementation. The faults initially form due to strong tectonic activities. During faulting, the fault breccia and gouge form the fault core, the fault pumping process leads to large amounts of fluid penetrating the deep crust, and the faults become the conduits for surface fluids (Figure 13A). The faults also can transport the oil and gas during this stage, which, however, cannot be accumulated due to the poor fault sealing capacity of the faults. The fault core is cemented by the mixture of different sources of fluid when the faults stop being active and the damage zone becomes the major region of fluid migration. Based on permeability studies of the fault zone (Faulkner et al., 2010; Indrevær et al., 2014), two sides of the damage zone are cemented firstly due to the relatively lower permeability compared with the middle part (Figure 13B). The mixture of surface fluids and deep-source hydrothermal fluids changes the physicochemical conditions of the fault zone, leading to different types of cementation of the fractures of the damage zone, which occurs first in the upper part of the faults. Sealed by the partially cemented damage zone, the oil and gas start to accumulate. The sealed area of the damage zone expands with increasing fault rest time and more hydrocarbon reservoirs form (Figure 13C). At last, the whole damage zone will be cemented; the faults show an extremely good sealing capacity for oil and gas (Figure 13D).

6. Conclusions Geochemical studies of different components of the fault zone were conducted

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on the Hong-Che Fault Zone of the Junggar Basin in northwestern China. Two main conclusions can be drawn: (1) Faults are important conduits for fluid migration and different components of the fault zone show distinct geochemical characteristics due to strong fluid–rock interaction. The major elements of the Hong-Che Fault Zone suggest that the fault core has higher LOI, potassium loss, CIA, and PIA values than the damage zone, implying that the fault core experienced more serious elemental loss and weathering than the damage zone. Most of the HFSE, LILE, and REE contents of the fault core are relatively lower than that of the damage zone, suggesting that fault activities might lead to a notable loss of trace elements in the fault core. The carbon and oxygen isotope data reveal that the cementation of the Hong-Che Fault Zone is due to multiple sources of fluid and mainly deep-source hydrothermal fluids affected the fault core. (2) In combination with previous studies, we suggest a potential fault-cemented sealing process for a period of fault movement. During faulting, the fault core acts as conduit for the fluids. The fault core is cemented after faulting and the damage zone becomes the major conduit. The cementation firstly occurs on two sides of the damage zone in the upper part of the faults based on permeability and geochemical studies and then expands to the whole fault. This process explains the relationship between the fault-cemented sealing and the oil and gas accumulation.

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Acknowledgements The authors want to thank the Xinjiang Oilfield Company (PetroChina) for providing the original data. We thank the editors Dr. Michel Faure and Miss Diane Chung, the reviewers Dr. Masakazu Niwa and Dr. Flavien Choulet for their kind help and suggestions for improving the manuscript. This research is supported jointly by the China Postdoctoral Science Foundation (Grant No.2016M592265), Shandong Provincial Natural Science Foundation, China (ZR2016DB14), Talent Introduction Project of China University of Petroleum (YJ201601026) and the National Natural Science Foundation of China (Grant No. 41272142).

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Figure captions

Figure 1. Sketch maps (a) showing the tectonic location of the Junggar Basin in the CAOB (modified after Xu et al., 2015), the major faults and tectonic units (b) in and around the basin and the fault system of the Hong-Che Fault Zone (c). Select seismic line is marked and shown in Figure 2.

Figure 2. Uninterpreted (top) and interpreted (bottom) seismic profile across the Hong-Che Fault Zone. The location of the profile is marked in Figure 1c. The abbreviation in the figure: N1s represents the bottom of Shawan Formation; K1tg represents the bottom of Tugulu Group; J1b represents the bottom of Badaowan Formation; T2k is the bottom of Karamay Formation; T1b is the bottom of Baikouquan Formation; C-top represents the top of the Carboniferous.

Figure 3. Stratigraphic sequences and lithology of the western margin of the Junggar Basin. Courtesy of the Xinjiang Oilfield Company (PetroChina). The colors in the figure represent the colors of rocks.

Figure 4. The lithological column showing the location of samples in the Hong-Che Fault Zone. The vertical axis is depth, and the units are in meters. The colors in the figure represent the colors of rocks.

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Figure 5. Core samples and thin sections of the Hong-Che Fault Zone. (A) the fault breccia in the fault core, Hongqian 12 well, 379.39m. (B) the cemented cataclasite in the fault core, Hong 44 well, 2298m. (C) the alternated cataclasite in the fault zone, Hongqian 12 well, 615.2m. (D) multi-phase of highly filled hydrothermal veins in the damage zone, Hongqian 12 well, 414.1m. (E) the calcite and zeolite filled in the veins of the fault core, Pai 66 well, 1206.6m. (F) multi-phase of quartz veins in the damage zone, Hongqian 12 well, 562m. (G) scanning electron micrograph showing the clay minerals (cholorite, illite and sectite), Pai 66 well, 1205m. (H) scanning electron micrograph showing the chlorite in the fault core, Pai 66 well, 1205m. (I) microscope photos showing the sericitization of feldspar in the fault core, Che 47 well, 3255.6m. (J) showing the totally alternated fault core in the Hongqian12 well, 651.1m. (K) thin section under the microscope showing the cataclasite in the fault core, with obviously fractures and offset of feldspars, Hong63 well, 1737.2m. (L) microscope photos showing the cataclasite in the fault core, the fractures cut off the lithic fragments, Hong44 well, 2298.7m. (M) showing the fault core of Hong 63 well at 1737.2m, and an obvious boundary exists between the cataclasite and the serpentine alternation rocks. (G) and (H) are from Shengli Oilfield Company.

Figure 6. The content range of major (A) and trace elements (B) in the fault core and damage zone.

40

Figure 7. Primitive mantle-normalized incompatible trace elements spider diagram (A) and Chondrite-normalized REE patterns (B) for basalts from the Hong-Che Fault Zone. Chondrite and primitive mantle values are from McDonough and Sun (1995). Average data of OIB, EMORB and NMORB are from Sun and McDonough (1989). PAAS data are from Mclennan et al. (1993). OIB is the ocean island basalt, EMORB is enriched mid-ocean ridge basalt, NMORB is normal mid-ocean ridge basalt, PAAS is post-Archean Australian Shale.

Figure 8. Zr/TiO2-SiO2 (A) and SiO2-K2O (B) (Gill, 1981) diagrams for the fault core and damage zone of the Hong-Che Fault Zone.

Figure 9. Ternary diagram of CaO+Na2O, Fe2O3T+MgO, K2O (A) (after Escuder et al., 2004) showing the evolution trend of fault core and damage zone. (B) A-CN-K ternary diagram (after Fedo et al., 1995) showing the weathering degree of fault core and damage zone.

Figure 10. Concentration variation diagrams of selected trace elements versus Zr contents for fault core and damage zone in the Hong-Che Fault Zone.

Figure 11. Nb/Y-Zr/TiO2 diagram of Winchester and Floyd (1977) for the classification of volcanic rocks.

41

Figure 12. The δ18OVMOW-δ18CVPDB diagram showing the source of hydrothermal fluids. The data areas are based on Taylor et al. (1967), Hoefs (2008), Veizer and Hoefs (1976), Toyoda et al. (1994), Cao et al. (2007), Liu and Liu (1997) and Liu et al. (2004).

Figure 13. Conceptual model for explaining the fault sealing process.

42

43

44

45

46

47

48

49

50

51

52

53

54

Table 1 The samples from different components of fault zone architecture Sampl e HC-0 1 HC-0 2

Well

3254.7

Che47

3255.6

Hongqian1

3

2

HC-0

Hongqian1

4

2

HC-0

Hongqian1

5

2

HC-0

Hongqian1

6

2

HC-0

Hongqian1

7

2

HC-0

Hongqian1

8

2

9 HC-1 0 HC-1

m

Che47

HC-0

HC-0

Depth/

524.9 562 379.79 379.09 381.6 347.53

Che40

1392.6

Hongqian8

556.25

Hong44

2298.7

Horizon Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero us Carbonifero

Components of fault

Description

zone fault core fault core damage zone damage zone

fault breccia, with fair orientation, some mineral particles were offset by small fractures. Breccia were cemented by multiphase of calcite veins and tuff. Slightly weathered. fault breccia, with fair orientation, some mineral particles were offset by small fractures. Breccia were cemented by multiphase of calcite veins and tuff. Slightly weathered. dark grey tuff, with multiphase of veins, including calcite, zeolite and so on, slightly weathered. dark grey tuff, with multiphase of veins, including calcite, zeolite and so on, slightly weathered.

fault core

cataclasite, with abundant calcite veins

fault core

fault breccia, cemented by calcite veins and fault gouge

damage zone

dark grey tuff, with multiphase of veins, mainly calcite veins, slightly weathered.

damage zone

dark grey tuff, with multiphase of veins, mainly calcite veins, slightly weathered.

damage zone

black grey tuff, with multiphase of veins, slightly weathered.

fault core

cataclasite, light grey, fragments, with obvious striation on the surface of fragments.

fault core

cataclasite, dark grey, fragments, with striation on the surface of fragments.

55

1 HC-1 2 HC-1 3 HC-1 4 HC-1 5 HC-1 6 HC-1 7 HC-1 8 HC-1 9

us Carbonifero

Hong63

1845

Hong63

1737.2

Hong63

1582.7

Pai66

2129.6

Pai66

Pai66

us Carbonifero us Carbonifero us Carbonifero us Carbonifero

1205

us

1206.6

Pai666

1018.7

Pai666

1116.9

fault core

cataclasite, dark grey, fragments, cemented by calcite veins, andesite

fault core

cataclasite, dark grey, fragments, cemented by calcite veins, andesite

fault core

cataclasite, dark grey, fragments, cemented by calcite veins, andesite

damage zone

black carbonaceous mudstone, with obvious striation and step, filled by calcite veins fault breccia, with fair orientation, some mineral particles were offset by small fractures.

fault core

Breccia were cemented by multiphase of calcite veins and tuff. With dissolved pore, weathered.

Carbonifero us

fault breccia, with fair orientation, some mineral particles were offset by small fractures. fault core

Breccia were cemented by multiphase of calcite veins and tuff. With dissolved pore, weathered.

Carbonifero us Carbonifero us

damage zone

maroon andesite, with fractures filled by multiphase of calcite veins

fault core

cataclasite, cemented by calcite veins, slightly weathered.

Table 2 The contents (%) of major elements from different components of fault zone architecture

Al2O3

HC-01

HC-02

HC-03

HC-04

14.34

18.08

13.51

15.99

HC-0 5 7.48

HC-06

HC-07

HC-08

15.82

14.83

14.72

56

HC-0 9 15.20

HC-10

HC-11

HC-12

HC-13

15.92

14.72

16.80

16.40

HC-1 4 17.00

HC-16

HC-17

13.65

13.25

As2O3

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

BaO

0.03

0.02

0.02

0.06

0.01

0.05

0.10

0.06

0.03

0.09

0.03

<0.01

<0.01

0.01

0.01

<0.01

CaO

15.52

8.71

5.57

7.09

36.5

1.15

2.26

4.89

1.08

0.37

3.35

6.41

4.47

8.41

8.50

7.83

Cl

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

0.04

0.06

CoO

0.01

0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

Cr2O3

0.01

0.01

0.02

<0.01

0.01

<0.01

0.01

<0.01

0.01

0.02

0.02

0.01

0.01

0.01

0.01

0.01

CuO

0.05

0.01

<0.01

<0.01

<0.01

0.01

0.01

<0.01

<0.01

<0.01

0.01

0.08

0.01

0.01

<0.01

0.01

7.61

9.37

5.56

4.58

0.97

5.10

8.93

6.82

4.45

5.95

4.89

9.05

9.39

9.52

4.60

6.40

K2 O

0.42

0.42

1.02

1.54

0.32

2.24

2.82

1.96

3.16

1.72

1.42

0.09

0.16

0.15

0.82

0.80

MgO

4.40

5.39

1.60

1.42

0.53

1.90

2.24

2.12

1.58

1.81

2.61

4.31

4.24

5.44

2.19

2.43

MnO

0.10

0.14

0.12

0.11

0.11

0.12

0.16

0.16

0.06

0.13

0.07

0.15

0.18

0.15

0.10

0.09

Na2O

2.92

3.25

4.24

3.43

1.21

5.31

3.03

4.27

4.02

2.31

5.04

6.05

6.61

4.36

2.07

2.05

Fe2O3 T

NiO

0.01

0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

0.01

0.01

<0.01

<0.01

<0.01

<0.01

<0.01

P2O 5

0.13

0.16

0.14

0.12

0.04

0.17

0.24

0.20

0.15

0.16

0.15

0.14

0.14

0.13

0.16

0.13

PbO

0.01

0.01

<0.01

<0.01

<0.01

0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

SiO 2

42.66

50.54

60.65

56.58

21.48

63.79

57.51

57.58

64.26

65.25

63.06

52.24

53.94

47.97

53.59

53.65

SnO2

0.01

<0.01

0.01

<0.01

<0.01

0.01

0.01

0.01

0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

SO3

4.02

0.23

0.12

0.06

0.08

0.35

3.58

0.58

0.09

0.40

0.84

0.14

0.08

0.11

0.01

0.05

SrO

0.08

0.08

0.02

0.03

0.04

0.04

0.03

0.04

0.01

0.02

0.01

0.01

0.02

0.03

0.01

0.01

TiO 2

0.73

0.86

0.65

0.60

0.11

0.66

0.81

0.85

0.69

0.80

0.62

0.73

0.80

0.86

0.63

0.70

V 2O5

0.04

0.04

0.02

0.01

<0.01

0.02

0.02

0.02

0.01

0.02

0.02

0.04

0.04

0.05

0.02

0.03

ZnO

0.01

0.01

0.01

0.01

<0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

<0.01

<0.01

ZrO 2

0.01

0.01

0.02

0.03

0.01

0.02

0.02

0.02

0.02

0.02

0.02

0.01

0.01

0.01

0.01

0.01

LOI

9.62

3.56

5.78

7.43

30.86

2.96

5.72

4.98

4.41

4.50

4.30

3.04

3.22

5.03

13.02

11.61

57

SUM

102.74

100.92

99.08

99.09

99.76

99.74

102.34

99.29

99.25

99.51

101.20

99.31

99.73

99.26

99.44

99.12

CIA

58.77

61.86

47.30

55.25

63.4

54.42

54.98

47.65

55.89

71.54

48.04

45.65

46.10

53.96

63.94

63.52

PIA

59.11

62.24

47.07

55.93

64.2

63.09

61.45

47.28

65.10

81.59

53.31

45.63

51.50

54.00

65.20

64.74

CIA= [Al2O3/(Al2O3+CaO*+Na2O+K2O） ]*100 (molar proportions), Nesbitt and Young, 1982. PIA= [(Al2O3-K2O)/(Al2O3+CaO*+Na2O-K2O） ]*100 (molar proportions), Fedo et al., 1995. CaO* represents the CaO content in the silicate fraction. After correcting for P2O5 , if the mole fraction of CaO≦Na2O, then CaO*= CaO; if CaO≧Na2O, then CaO*= Na2O. Bock et al., 1998.

Table 3 The contents (ppm) of trace elements from different components of fault zone architecture Detection limits

HC-01

HC-02

HC-03

HC-04

HC-05

HC-06

HC-07

HC-08

HC-09

HC-10

HC-11

HC-12

HC-13

HC-14

HC-16

HC-17

La

0.5

3.5

4.1

14.6

21.3

3.8

16.5

23.2

12.3

19.7

10.2

15.5

5.2

5.2

3.7

9.3

9.3

Ce

0.5

9.5

10.6

30.8

47.6

8.1

34.5

48.6

28.7

45.8

22.5

32.3

13.5

12.8

9.8

20.8

20.6

Pr

0.03

1.35

1.56

3.69

5.38

0.90

4.06

5.66

3.78

5.48

2.86

4.14

1.85

1.76

1.36

2.60

2.59

Nd

0.1

6.7

7.6

15.9

22.0

3.8

16.7

23.6

17.2

23.0

12.9

17.1

9.1

8.8

7.1

11.3

11.0

Sm

0.03

1.85

2.04

3.76

4.75

0.88

3.69

5.14

4.40

5.16

3.42

3.84

2.40

2.31

2.01

2.75

2.66

Eu

0.03

0.73

0.83

1.12

1.06

0.24

0.98

1.40

1.35

1.33

1.03

1.12

0.84

0.82

0.86

0.83

0.76

Gd

0.05

2.03

2.33

3.81

4.35

0.82

3.52

4.92

4.53

4.66

3.54

3.64

2.78

2.59

2.41

2.58

2.26

Tb

0.01

0.32

0.36

0.59

0.67

0.13

0.53

0.74

0.75

0.74

0.54

0.54

0.43

0.39

0.38

0.40

0.35

Dy

0.05

2.01

2.32

3.73

4.40

0.83

3.51

4.74

4.97

4.62

3.64

3.54

2.82

2.55

2.45

2.61

2.12

Ho

0.01

0.45

0.50

0.78

0.95

0.18

0.75

0.99

1.06

0.97

0.79

0.76

0.60

0.57

0.53

0.56

0.45

Er

0.03

1.27

1.42

2.25

2.73

0.53

2.20

2.79

3.14

2.83

2.38

2.19

1.81

1.68

1.46

1.59

1.25

Tm

0.01

0.19

0.21

0.34

0.42

0.08

0.34

0.41

0.47

0.43

0.38

0.34

0.27

0.25

0.21

0.23

0.19

58

Yb

0.03

1.20

1.35

2.21

2.81

0.51

2.28

2.68

2.95

2.75

2.52

2.19

1.68

1.63

1.33

1.48

1.24

Lu

0.01

0.18

0.21

0.34

0.44

0.08

0.36

0.43

0.47

0.43

0.39

0.34

0.26

0.25

0.21

0.22

0.19

Rb

0.2

5.0

5.7

22.5

30.3

6.7

50.2

57.3

36.6

86.4

31.4

18.0

2.3

3.3

2.3

26.9

32.3

Ba

0.5

248

187.0

258

539

190.5

421

984

558

319

777

281

17.9

29.6

121.5

177.5

123.5

Th

0.05

0.27

0.34

2.35

7.00

0.77

5.40

4.40

2.04

4.38

1.75

3.73

0.68

0.72

0.38

1.30

1.37

U

0.05

0.10

0.14

0.87

2.38

0.40

2.61

1.36

0.73

1.42

0.67

1.25

0.22

0.24

0.13

0.43

0.40

Nb

0.2

0.7

0.8

3.0

8.4

0.9

5.5

5.6

2.8

6.6

2.3

4.5

1.2

1.1

0.7

1.6

1.5

Ta

0.1

<0.1

<0.1

0.2

0.5

<0.1

0.3

0.3

0.1

0.3

0.1

0.3

<0.1

<0.1

<0.1

<0.1

<0.1

Cr

10

60

60

110

20

10

30

30

20

30

30

150

70

60

100

40

120

Cs

0.01

0.09

0.15

0.73

0.98

2.41

1.08

2.23

0.56

4.68

0.50

0.40

0.16

0.13

0.14

0.79

0.70

Ga

0.1

14.2

17.8

16.4

16.9

6.2

17.9

19.8

17.8

20.1

17.8

16.9

21.1

18.3

17.4

13.7

13.2

Hf

0.2

0.9

1.1

2.9

5.9

0.7

3.9

4.1

3.4

4.6

3.4

3.7

1.5

1.5

1.1

2.1

1.9

Sn

1

1

1

10

2

1

2

2

2

2

1

1

1

1

1

1

1

Sr

0.1

665

595

248

304

372

373

272

345

139.5

182.0

93.5

117.0

225

292

119.5

133.5

V

5

244

266

130

95

19

129

177

154

110

127

105

254

269

312

147

221

W

1

<1

<1

1

1

<1

1

1

1

1

1

1

1

<1

<1

1

<1

Y

0.5

13.0

14.1

23.7

28.7

5.7

23.3

29.9

31.8

30.0

24.3

23.0

17.8

16.7

14.9

17.0

13.8

Zr

2

31

37

104

220

26

137

154

116

179

119

133

52

51

37

74

66

ΣREE

31.3

35.4

83.9

118.9

20.9

89.9

125.3

86.1

117.9

67.1

87.5

43.5

41.6

33.8

57.3

55.0

ΣLREE

23.6

26.7

69.9

102.1

17.7

76.4

107.6

67.7

100.5

52.9

74.0

32.9

31.7

24.8

47.6

46.9

ΣHREE

7.65

8.70

14.1

16.8

3.16

13.5

17.7

18.3

17.4

14.2

13.5

10.7

9.91

8.98

9.67

8.05

ΣLREE/ΣHREE

3.09

3.07

4.97

6.09

5.61

5.67

6.08

3.69

5.76

3.73

5.47

3.09

3.20

2.77

4.92

5.83

δEu*

1.15

1.16

0.90

0.70

0.85

0.82

0.84

0.92

0.81

0.90

0.90

0.99

1.02

1.19

0.94

0.92

δCe

1.05

1.01

0.99

1.04

1.02

0.99

0.99

1.01

1.05

0.99

0.95

1.05

1.02

1.05

1.00

1.00

(La)N/(Yb)N

2.0

2.1

4.45

5.11

5.0

4.88

5.84

2.81

4.83

2.73

4.77

2.1

2.2

1.9

4.2

5.1

59

(La)N/(Sm)N

1.2

1.3

2.44

2.82

2.7

2.81

2.84

Th/U

2.7

2.4

2.7

2.94

1.9

2.07

Y/Ho

29

28

30

30

32

31

*

1.76

2.40

1.88

2.54

1.4

1.4

1.2

2.1

2.2

3.24

2.8

3.08

2.6

2.98

3.1

3.0

2.9

3.0

3.4

30

30.0

31

31

30

30

29

28

30

31

*

*δEu=Eu/Eu =(Eu)N/[(1/2)((Sm)N+(Gd) N); δCe=Ce/Ce =(Ce)N/[(1/2)(La)N+(Pr)N). N in the subscript represents the chondrite-normalized data.

Table 4 Carbon and oxygen isotope data from different components of the Hong-Che Fault Zone Components of fault zone Sample δ13CvPDB δ18OvSMOW HC-03

damage zone

-10.3

HC-04

damage zone

-6.6

HC-05

fault core

-7.3

HC-08

damage zone

-8.3

HC-13

fault core

-18.4

HC-14

fault core

-13.8

HC-15

damage zone

-10.1

HC-16

fault core

-15.4

HC-17

fault core

-15.5

HC-18

damage zone

-9.4

HC-19

fault core

-7.1

15.7 16.4 2.7 4.8 13.0 13.8 18.0 8.5 7.6 17.7 14.0

Table 5 t-test of main elements and parameters of the Hong-Che Fault Zone t Stat

P (2-tailed)

Al2O3

0.01

0.99

CaO

1.57

0.14

0.48 -2.93

Fe2 O3 K2O

T

t Stat

P (2-tailed)

PIA

1.09

0.31

La

-4.14

0.00

0.64

Ce

-4.38

0.00

0.02

Nd

-5.04

0.00

60

MgO

2.74

0.02

Rb

-2.39

0.05

MnO

-0.01

0.99

Ba

-2.08

0.08

Na2O

-0.09

0.93

Th

-2.48

0.04

P2O5

-1.34

0.23

Nb

-2.88

0.03

SiO2

-1.95

0.07

Cr

1.14

0.28

SrO

0.62

0.55

Cs

-1.56

0.18

TiO2

-0.49

0.63

Hf

-3.51

0.01

ZrO2

-3.79

0.01

Sr

0.38

0.71

LOI

1.05

0.32

Y

-5.67

0.00

CIA

1.61

0.13

Zr

-3.47

0.01

61

Highlights
Fault core has more serious elemental loss and higher weathering degree than the damage zone.
The cements of the Hong-Che Fault Zone were formed by multiple source of fluids.
A possible fault sealing process was put forward.

62

Graphical abstract

63