Detrital Zircons UPb Age and Hf Isotope from the Western Side of the Taiwan Strait : Implications for Sediment Provenance and Crustal Evolution of the Northeast Cathaysia Block

In situ detrital zircons U-Pb and Hf isotope analyses from the Min and Jiulong River of Southeast China were carried out to identify sediment provenance and crustal evolution of the northeast Cathaysia Block. Detrital zircons from both rivers displayed similar spectrum peaks at 236, 155, and 110 Ma, but samples from the Min River displayed a distinct Caledonian peak (ca. 460 Ma) and contained more Precambrian particles (ca. 1.8 Ga), which likely stemmed from the upstream area of the Wuyishan terrain. Interestingly, because Taiwan Island cannot supply Caledonian and Paleoproterozoic detrital materials and because the Ou and Jiulong River also lack components from these two populations, it is highly likely that the sediment in the western Taiwan coast partially originates from the Min River. The sediments from the Min River in Fujian are also considered the most likely source of the beach sands of western Taiwan (Chen et al. 2006). However, we stress that the ~1.8 Ga age source in the western Taiwan sediments was found and recognized. Combining U-Pb dating and Hf-isotope suggests that the northeast Cathaysia Block contains some Neoarchean detrital zircons, which derived from the incorporation of juvenile mantle materials and re-melting of ancient crustal substances. The wide ranges of εHf(t) value in the Paleoproterozoic and Neoproterozoic demonstrate the re-melting of ancient crustal materials with minor juvenile mantle materials. Phanerozoic zircons stemmed from re-melting and recycling of Proterozoic crustal materials with or without the invasion of juvenile mantle-derived magmas.


INTRODUCTION
The Taiwan Strait connects the East China Sea and South China Sea, which are two major marginal seas of the western Pacific.This region serves as a canonical area in investigating terrigenous detrital materials transported into the sea, including the provenance and flux, as well as their distribution, transport and dispersion in continental shelves (Liu et al. 2002;Dadson et al. 2003;Xu et al. 2009).Detrital sediments from exposed continental crust across drainage basins may provide a record of the paleogeographic setting and their surrounding source regions (Cawood et al. 2003;Veevers et al. 2005).
Detrital zircons are resistant to chemical weathering and mechanical abrasion, and thus survive weathering from their provenance and subsequent transportation in fluvial systems.Therefore, in situ zircon U-Pb dating and Hf-isotope analysis has proven to be a useful tool in assessing the distribution of source rocks in the provenance and reconstructing tectonic evolution of continental blocks (Condie et al. 2005;Iizuka et al. 2005;Veevers et al. 2005;Yang et al. 2009;Wang et al. 2011).Chen et al. (2006) proposed that sediments from the Min River in Fujian, Southeast China, are considered the most likely source of the beach sands of W Taiwan.However, ca.1.8 Ga monazites have not been discovered in the Min River estuary and Wuyishan area (Chen et al. 2006(Chen et al. , 2008)).The Min River and Jiulong River are the major waterways flowing into the Taiwan Strait from the west and supply the strait with large amounts of terrigenous detrital materials (Xu 1994;Liu et al. 2001).In this study, we present U-Pb and Hf-isotope analyses of detrital zircons from the Min and Jiulong Rivers.The isotopic data are used to decipher identify sediment provenance and reveal the crustal evolution of the northeast Cathaysia Block.

GENERAL GEOLOGY OF THE DRAINAGE BASINS
The South China continent is composed of the Yangtze Block in the northwest and the Cathaysia Block in the southeast, along the Jiangshao-Pingyu Fault (Fig. 1a).The Min River flows across northern Fujian (Fig. 1b).As the largest river in the province it has a drainage basin area of 61000 km 2 , an average flow of 1750 m 3 s -1 and annual average sediment loads of 715.5 × 10 4 t (Liu et al. 2001).The Jiulong River is situated in southern Fujian and is the second largest river in the province.The river has a drainage basin area of 14700 km 2 and annual average sediment loads of 223 × 10 4 t (Xu 1994).Because both drainage basins are mainly characterised by mountains and hills and concentrat-ed rainfall, large quantities of terrigenous detrital materials are expected to be transported into the Taiwan Strait.
Precambrian basement rocks in the Cathaysia Block are sparsely exposed in the Chen Cai, Badu, Wuyishan, Nanling, Yunkai and Hainan areas (Zhao and Cawood 2012).The Min River originates from the Wuyishan region, which is a major Precambrian outcropping area of the Cathaysia Block (Fig. 1b).The headstream of the Jiulong River is located in the Longyan region (eastern Nanling).The Cathaysia Block has no exposed Archean rocks, but numerous Archean detrital zircons and minor inherited or xenocrystic zircons, implying the existence of Archean crust underlying the block or adjacent regions (Wan et al. 2007;Yu et al. 2009Yu et al. , 2012)).The Cathaysia Block basement is composed mainly of Neoproterozoic basement rocks (~90%) with a minor outcrop of Paleoproterozoic rocks (Badu Group) in Wuyishan, and Mesoproterozoic rocks (Baoban, Shilu Group) in Hainan Island (Yu et al. 2010;Zhao and Cawood 2012).This composition is exemplified by ancient rock outcrops, which have been dated to approximately 1.8 Ga, in the Badu Group of southwestern Zhejiang and northwestern Fujian (Li et al. 1998;Yu et al. 2009Yu et al. , 2012)).The Cathaysia Block has been bear strong overprinting of middle Paleozoic (Caledonian), Triassic (Indosinian) and Jurassic-Cretaceous (Yanshanian) (Chen and Jahn 1998;Zhou 2003;Wang et al. 2013).Early Palaeozoic granites are widespread in the eastern South China Block.Late Mesozoic granites from the Jurassic to Cretaceous display a migratory pattern from inland to coast  Sun (2006) .Abbreviation: JS-PY F, Jiangshao-Pingyu Fault; ZH-DP F, Zhenghe-Dapu Fault.(Zhou et al. 2006;Li and Li 2007;Xu 2008;Wang et al. 2013).The drainage basins of both rivers are approximately perpendicular to the orientation of the Cathaysia granitevolcanic belts flowing into the Taiwan Strait (Fig. 1b).

SAMPLE AND ANALYSIS
Two surface sediment samples were collected from the Min River and one from Jiulong River (Fig. 1b).Three samples were all dominated by medium-coarse-grained feldspars and quartz sand.After washing, magnetic sorting and heavy liquid separation, zircon grains were glued to one side of double-sided tape and mounted with epoxy resin to form targets.The cathodoluminesence (CL) emission images have been widely used to distinguish igneous zircons from metamorphic zircons.In order to investigate the internal structures of zircon particles, zircon CL imaging was taken using a scanning electron microprobe at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.
An Agilent 7500a quadruple (Q)-ICPMS and a Neptune multi-collector (MC) -ICPMS were used for simultaneous determination of zircon U-Pb age, trace elements and Lu-Hf isotopes with a 193 nm excimer ArF laser-ablation system (GeoLas Plus) attached.Experiments were carried out at the MC-ICPMS laboratory of the Institute of Geology and Geophysics, Chinese Academy of Sciences.The analytic methods and equipment parameters were similar to those of Xie et al. (2008).
The spot size of laser ablation was 44μm in diameter.U, Th and Pb concentrations were calibrated using 29 Si as an internal standard and NIST 610 as the reference standard (Pearce et al. 1997). 207Pb/ 206 Pb, 206 Pb/ 238 U, 207 Pb/ 235 U ( 235 U = 238 U/137.88)ratios were corrected using the 91500 external standard.GJ-1 and 91500 yielded weighted 206 Pb/ 238 U ages of 603 ± 8 and 1063 ± 17 Ma, respectively.The fractionation correction and results were calculated using GLIT-TER 4.0 (Jackson et al. 2004).Subsequently, common Pb was corrected according to the method proposed by Andersen (2002).The weighted mean U-Pb ages and concordia plots were processed using ISOPLOT 3.0 (Ludwig 2003).
In situ determination of zircon Lu-Hf isotopes was performed using a Neptune MC-ICPMS, which used a Geolas 193 ArF laser ablation system.In this study, the mean 173 Yb/ 171 Yb ratio of the individual spot is used to calculate the fractionation coefficient (β Yb ), and then derive the contribution of 176 Yb to 176 Hf (Iizuka et al. 2005).Detailed test procedures and equipment operating conditions were previously described (Wu et al. 2006).Interference corrections were facilitated using 175 Lu/ 176 Lu = 0.02655 and 176 Yb/ 172 Yb = 0.5887 (Wu et al. 2007).The 176 Lu decay constant required for the calculation of ε Hf (t) was 1.867 × 10 -11 y -1 (Söderlund et al. 2004).The 176 Hf/ 177 Hf and 176 Lu/ 177 Hf ratios of chondrite at the present day are 0.282785 and 0.0336, respectively (Bouvier et al. 2008).To calculate model ages based on a depleted-mantle source, we have adopted a model with 176 Hf/ 177 Hf = 0.28325 (Griffin et al. 2002) and 176 Lu/ 177 Hf ratio of 0.0384 (Griffin et al. 2000).GJ-1 and Mud Tank zircons give weighted 176 Hf/ 177 Hf ratios of 0.282009 ± 20 (2σ) and 0.282504 ± 15 (2σ), respectively.Hf isotopic composition is calculated using the following equations:

RESULTS
Detrital zircons are characterized by euhedral, short prismatic shapes, with oscillatory bands in the CL images (Fig. 2).A few zircons display unzoned or cloudy-zoned CL image patterns.Most zircons had Th/U ratios greater than 0.10 (only five particles Th/U ratios less than 0.10).More than 60 zircons were conducted for each sample to satisfy statistical requirements (Vermeesch 2004;Andersen 2005).

U-Pb Ages Results
We used 207 Pb/ 206 Pb ages for zircons of age ≥ 1.0 Ga and 206 Pb/ 238 U ages for zircons of age < 1.0 Ga (Compston et al. 1992).It is worth noting that only analyses with less than 10% discordance were included in the following discussion.

Min River (MJ01)
A total of 146 analyses of 146 grains from the Min River estuary were made, of which 126 analyses are concordant with ages ranging from 2765 ± 12 to 97 ± 2 Ma (Appendix 1).The age distributions of detrital zircon exhibited four major groups (Figs.3a and b): 1.6 -1.9 Ga (16.7%), .In addition, two zircon grains with magmatic internal zoning structures show Neoarchean ages of 2506 ± 10 and 2765 ± 12 Ma, and nine detrital zircons belong to the Neoproterozoic (613 -919 Ma).

Jiulong River (JL01)
A total of 80 analyses of 80 grains from the Jiulong River estuary were undertaken, of which 73 analyses were concordant.The concordant zircons ranged in age from 2577 ± 9 to 101 ± 4 Ma (Appendix 1).Two major groups can be identified (Figs.3e and f): 101 -197 Ma (56.2%) and 207 -254 Ma (20.5%).The third largest age population was made up of 5 grains with a range of 1474 -1675 Ma.Few Caledonian and Paleoproterozoic zircons have been discovered in Jiulong River estuary.

Zircon Hf Isotopic Results
Almost all of the zircons had 176 Lu/ 177 Hf ratios of less than 0.002, indicating that the zircons had a minimal extent of radioactive Hf accumulation after their formation.Hence, the present-day 176 Hf/ 177 Hf ratios of the zircons are representative of the 176 Hf/ 177 Hf ratios upon formation of the zircons (Amelin et al. 1999).The analytical results are summarized in Appendix 2.
Detrital zircons from the Min River showed a large variation in Hf isotopic compositions (0.280856 -0.282816), with ε Hf (t) values varying from +11.5 to -21.1 (Fig. 4a).Min River zircons chiefly fall in the negative epsilon space, but only 24 zircons (11%) with positive ε Hf (t). Figure 4b shows the distributions of the two-stage Hf (T DM2 ) model ages.It can be seen that the crustal model age shows two prominent groups of 3.2 -2.6 and 2.0 -1.4 Ga from the two samples in Min River.
Detrital zircons from the Jiulong River estuary had 176 Hf/ 177 Hf ratios in the range of 0.280902 -0.282842.The majority of particles had ratios greater than 0.282010, corresponding to an age range of 101 -800 Ma and ε Hf (t) values between -12.7 and +6.1 (Fig. 4c).A few zircons had ratios less than 0.282010, corresponding to an age range of 932 -2577 Ma and ε Hf (t) values between -5.5 and -15.8.The Jiulong River also shows a large abundance of negative and some positive ε Hf (t) values of 275 -100 Ma (Fig. 4c).Zircons from the Jiulong River show a significant number of zircons with T DM2 between 1.2 and 1.8 Ga (Fig. 4d).

Provenance Tracing
U-Pb age analysis revealed that the detrital zircons from the Min River contained a large proportion of Precambrian particles (37%).In particular sample MJ16 has a clear peak age corresponding to the Paleoproterozoic (1874 Ma).This feature is related to the fact that the Badu Group with a Paleoproterozoic basement extensively outcrops in the Min River upstream basin (Li et al. 1998;Yu et al. 2009Yu et al. , 2012)).In addition, nine Neoarchean detrital zircons are found in this study, which also have been identified in Wuyishan terrain as inherited or xenocrystic zircons (Wan et al. 2007;Yu et al. 2009Yu et al. , 2012)).Recent SHRIMP U-Pb zircon dates demonstrated that northeast Cathaysia has undergone tectonothermal events in Neoproterozoic (Shu et al. 2011), which could provide Neoproterozoic material.In contrast, the Jiulong River estuary contains a sporadic number of Precambrian particles (Fig. 3f).
The Cathaysia Block was impacted by the Caledonian, Hercynian-Indosinian and Yanshanian (Jurassic-Cretaceous) orogenies (Zhou et al. 2006;Xu 2008), which are widespread in the eastern South China Block (Fig. 1b).The proportion of Phanerozoic detrital zircons in the mouth of the Min River is (e) (f) significantly higher than that ones in the upstream.The Caledonian granites are well developed throughout the Wuyishan terrain (Zhou 2003;Wan et al. 2007).Consequently, a considerable proportion (23%) of the detrital zircons in the Min River displayed prominent Caledonian traits.
A few Hercynian-Indosinian granites are exposed in Zhenghe, Mingxi and Liancheng in Fujian Province (Sun 2006) (Fig. 1b).The monazite age (Chen et al. 2008) and the zircons U-Pb age (Xu et al. 2007;Yu et al. 2012), were recently reported using sand samples from east of Wuyishan terrain, demonstrating the presence of Indosinian materials.The Indosinian granites are also exposed in the Longyan area (Zhao et al. 2006;Guo et al. 2012;Wang et al. 2013).These areas possibly provide the source of Indosinian components to the Min River and Jiulong River.From Jurassic to Cretaceous, this granite belt migrated from inland toward the coast (Zhou et al. 2006;Xu 2008).So, both the Min and Jiulong River contain a large number of Mesozoic zircons.
The detrital sediments in the Min River estuary mainly originate from the Jurassic-Cretaceous rocks in the middlelower reaches.Those are also partially derived from the Indosinian and Caledonian components of its upstream re-gion, together with Precambrian basement material from the headstream area.In contrast, the source of the detrital sediments in the Jiulong River estuary is mainly the Jurassic-Cretaceous rocks from the middle-lower reaches of the river, with a minor contribution from the Mesoproterozoic and Hercynian-Indosinian materials of the upstream region.

Re-Assessing the Provenance of Sediments From
Western Coastal Areas of Taiwan Island The Min River plays a prominent role in transport and supply of deposits to the western Taiwan, where large quantities of monazites that have been dated to ca. 1.8 Ga (Chen et al. 2006).However, Precambrian monazite has not been discovered in the Min River estuary and Wuyishan area (Chen et al. 2006(Chen et al. , 2008)).Chen et al. (2008) challenged the theory of an early Proterozoic provenance in Taiwan and suggested that coastal deposits of western Taiwan may be under the control of other river systems (e.g., the Ou River; Xu et al. 2007) or other orogenic belts (Sano et al. 2006).
The Taiwan crust experienced five major tectonic-thermal events (Lan et al. 2008), which occurred in the early  Jurassic , late Jurassic (~153 Ma), late Cretaceous (97 -77 Ma) and prior to (56 -9 Ma) and after (< 5 Ma) the Pliocene, but no one in the Caledonian (360 -540 Ma).In contrast, monazites in beaches of western Taiwan (Miaoli-Hsinchu area) and southern Taiwan (Chiayi-Tainan area) show prominent Caledonian (430 Ma) features (Chen et al. 2006), suggesting that these materials are unlikely to have originated from the island of Taiwan.
Further constraints on provenance can be gained by various potential sources (Fig. 5).The Paleoproterozoic peak at ~1.8 Ga is ubiquitous in the Yangtze, Ou River and Min River (Figs. 5a, b, and c), but the ~2.5 Ga and 700 -900 Ma peaks are unique to the Yangtze (Yang et al. 2012).Neoproterozoic was an important period for the crust of the South China Block accretion and reworking (Li et al. 1995(Li et al. , 2002;;Wang et al. 2007).However, a ~420 Ma population appears to be distinctive of the Min River (Fig. 5c).Not surprisingly, the Yangtze clay mineral (< 2 μm) can be transported southward to Taiwan Strait by the China Coastal Current (Xu et al. 2009), but heavy minerals (i.e., monazite, zircon) to western Taiwan Island are limited.Zircons from the Ou River show the Paleoproterozoic and Cretaceous ages (Fig. 5b), but very few grains of the Paleoproterozoic and Caledonian were found in its estuary (Xu et al. 2007).
Our work broadly supports Chen et al. (2008), showing that the main sources of Taiwan sediment came from the Min River.According to Fig. 5 at ~1.8 Ga and ~420 Ma, which appear to be distinctive of the western Taiwan Island.Thus, the Min River likely supplies a portion of the detrital materials to western Taiwan beaches.Nevertheless, U-Pb ages revealed that the detrital zircons of the Jiulong River estuary do not have characteristic Precambrian and Caledonian peaks, indicating that this river is unlikely to provide materials to beaches of western Taiwan.Furthermore, based on the U-Pb ages and Hf isotopes of the detrital zircons of central Taiwan and compared the data with the U-Pb and ε Hf (t) data of the zircons in the Cathaysia Block (Lan et al. 2009), it was also clear that they have the same origin.Hence, the authors reasoned that the Min River plays a crucial role in the transportation and supply of detrital sediments to western Taiwan.

Implications for Crustal Evolution
The Ou River and the Min River in northeast Cathaysia Block both have a large number of Paleoproterozoic zircons, which contain information of the Paleoproterozoic basement (Wuyishan).However, the zircon U-Pb age and ε Hf (t) from Jiulong River are significantly different from these from Min River.Yu et al. (2010) suggested that the Cathaysia Block can be roughly divided into the Wuyishan area in the northeast and the Nanling-Yunkai-Hainan area in the southwest.Here, we just discuss the crustal evolution of northeast Cathaysia Block.
Whether the Cathaysia Block contains ancient crystalline basement remains controversial.Recently, Archean detrital zircons and minor inherited or xenocrystic zircons have been found in Wuyishan regions (Wan et al. 2007;Yu et al. 2009Yu et al. , 2012)).Yu et al. (2012) found a large proportion of Archaean zircons and 2.5 Ga) in the Badu Group Complex.In addition, some Archean debris had been discovered in Paleoproterozoic amphibolite in Jianning, Fujian (Li et al. 1998).In this study, nine Neoarchean detrital zircons (2504 -2765 Ma) in Min River were identified, with ε Hf (t) varying from +6.5 to -6.8.The two-stage Hf model age of the zircons in this age group is 2.6 -3.6 Ga (Fig. 4b), which suggested the juvenile crust of the Badu area in north Cathaysia was mainly formed in 2.5 -2.8 Ga (Yu et al. 2012).These data imply that the Neoarchean zircons include both juvenile mantle-derived components and the reworked crustal materials.
The ε Hf (t) values of Paleoproterozoic zircons exhibit a wide range from negative to positive (-16.1 to +3.9) (Fig. 4b), indicating that the northeast Cathaysia involved extensive reworking of older crust with litter juvenile crustal growth (Xu et al. 2007).Zircons with U-Pb ages of 1.5 -1.0 Ga were extremely rare, reflecting that the northeast Cathaysia Block experienced long-term tectonic stability during that period.The wide ranges in ε Hf (t) values (-14.2 to +2.6) in the Neoproterozoic indicated re-melting of ancient crustal material with minor juvenile mantle input.
The zircons of Neoproterozoic mafic rocks show positive ε Hf (t) values, suggesting that they originated from a depleted mantle source (Shu et al. 2011).In the groups spanning 100 -500 Ma, the northeast Cathaysia Block has been influenced by the Caledonian, Hercynian-Indosinian and Yanshanian orogenies.Most of Phanerozoic zircons (93%) have negative ε Hf (t) values, and only twelve grains have positive ε Hf (t) values.Their T DM2 values were predominantly within the range of 0.7 -2.5 Ga with wide ranges in Hf-isotope composition, indicating that the Phanerozoic zircons stemmed from re-melting and recycling of the Proterozoic crustal materials, with or without juvenile mantle-derived magmas (Liu et al. 2012;Wang et al. 2013).

CONCLUSIONS
(1) Detrital zircons from the Min River and Jiulong River display Indosinian and Jurassic-Cretaceous characteristic peaks indicating that the detrital sediments were mainly supplied by Indosinian material of the upstream regions as well as Jurassic-Cretaceous materials from the middle and lower reaches.In addition, the detrital zircons from the Min River estuary display a prominent Caledonian peak and contain greater proportion of Precambrian particles, implying that these detrital substances originated from the upstream area of Wuyishan.(2) Given that Taiwan Island cannot supply the Caledonian and Paleoproterozoic detrital material, and that the Ou and Jiulong River estuary lack components from these two periods, it is highly likely that the beach debris in western Taiwan coast partially originates from the Min River.Our study of zircons from Min River confirms the finding of Chen et al. (2006) that the sediments from the Min River in Fujian are considered the most likely source of the beach sands of the western Taiwan.However, we stress that the ~1.8 Ga age source in the western Taiwan sediments was founded and recognized.

APPENDIX 2
Hf isotope data for detrital zircons from Min River and Jiulong River.

Fig. 1 .
Fig. 1.Simplified map of major tectonic units in the South China (a) and geological map of the drainage basins of the Min River and Jiulong River in Fujian Province (b) revised from Sun (2006) .Abbreviation: JS-PY F, Jiangshao-Pingyu Fault; ZH-DP F, Zhenghe-Dapu Fault.

Fig. 4 .
Fig. 4. Left panels show U-Pb ages versus ε Hf (t) values plots of concordant zircons (a, c), right panels show histograms of the two-stage Hf model ages for the concordant zircons (b, d).The intersection of these lines with the DM curve represents the crustal model age (T DM2 ) of grains lying along the line.Abbreviation: DM, Depleted Mantle; CHUR, Chondritic Uniform Reaervoir.
(3) The northeast Cathaysia Block contains some Neoarchean detrital zircons, which derived from incorporation between juvenile mantle material and re-melt ancient crustal substances.Wide ranges in ε Hf (t) values in the Paleoproterozoic and Neoproterozoic indicated remelting of ancient crustal material with minor juvenile mantle materials.Phanerozoic zircons stemmed from remelting and recycling of the Proterozoic crustal materials with or without juvenile mantle-derived magmas.Acknowledgments This work was financially supported by the National Natural Science Foundation of China (NSFC 40906047 and 41106073), Scientific Research Foundation of Third Institute of Oceanography (SOA.NO. 2014015) and Natural Science Foundation of Fujian Province (2010J05096).We are grateful to Dr. Yanyan Zhou and Dr. Yueheng Yang for their assistance with the analyses.We also thank Mei-Fei Chu, Kuo-Lung Wang and one anonymous reviewer for their helpful comments.