Zircon ages and Hf isotopic compositions of plutonic rocks from the Central Tianshan (Xinjiang, northwest China) and their significance for early to mid-Palaeozoic crustal evolution

<div><p>We present new zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the crustal evolution of the Chinese Central Tianshan (Xinjiang, northwest China) in the early to mid-Palaeozoic. The Early Ordovician (ca. 475–473 Ma) granitoid rocks have zircon <i>ε_Hf</i>₍<i>_t</i>₎ values either positive (+0.3 to +9.5) or negative (−6.0 to −12.9). This suggests significant addition of juvenile material to, and coeval crustal reworking of, the pre-existing continental crust that is fingerprinted by numerous Precambrian zircon xenocrysts. The Late Ordovician–Silurian (ca. 458–425 Ma) rocks can be assigned to two sub-episodes of magmatism: zircon from rocks of an earlier event (ca. 458–442 Ma) has negative zircon <i>ε_Hf</i>₍<i>_t</i>₎ values (−6.3 to −13.1), indicating a predominantly crustal source; zircon from later events (ca. 434–425 Ma) has positive zircon <i>ε_Hf</i>₍<i>_t</i>₎ values (+2.6 to +8.9) that reveal a predominantly juvenile magma source. The Early Devonian (ca. 410–404 Ma) rocks have near-zero zircon <i>ε_Hf</i>₍<i>_t</i>₎ values, either slightly negative or positive (−1.4 to +3.5), whereas the Mid-Devonian rocks (ca. 393 Ma) have negative values (−11.2 to −14.8). The Late Devonian (ca. 368–361 Ma) granites are undeformed and are chemically similar to adakite but have relatively low negative whole-rock <i>ε_Nd</i>₍<i>_t</i>₎values (−2.4 to −5.3). We interpret the Early Ordovician to Mid-Devonian magmatic event to reflect combined juvenile crustal growth and crustal reworking processes via episodic mafic underplating and mantle–crust interaction. The Late Devonian episode may signify delamination of the over-thickened Chinese Central Tianshan crust.</p></div

Zinc, Iron, Manganese and Copper Uptake Requirement in Response to Nitrogen Supply and the Increased Grain Yield of Summer Maize

<div><p>The relationships between grain yields and whole-plant accumulation of micronutrients such as zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu) in maize (<i>Zea mays</i> L.) were investigated by studying their reciprocal internal efficiencies (RIEs, g of micronutrient requirement in plant dry matter per Mg of grain). Field experiments were conducted from 2008 to 2011 in North China to evaluate RIEs and shoot micronutrient accumulation dynamics during different growth stages under different yield and nitrogen (N) levels. Fe, Mn and Cu RIEs (average 64.4, 18.1and 5.3 g, respectively) were less affected by the yield and N levels. ZnRIE increased by 15% with an increased N supply but decreased from 36.3 to 18.0 g with increasing yield. The effect of cultivars on ZnRIE was similar to that of yield ranges. The substantial decrease in ZnRIE may be attributed to an increased Zn harvest index (from 41% to 60%) and decreased Zn concentrations in straw (a 56% decrease) and grain (decreased from 16.9 to 12.2 mg kg⁻¹) rather than greater shoot Zn accumulation. Shoot Fe, Mn and Cu accumulation at maturity tended to increase but the proportions of pre-silking shoot Fe, Cu and Zn accumulation consistently decreased (from 95% to 59%, 90% to 71% and 91% to 66%, respectively). The decrease indicated the high reproductive-stage demands for Fe, Zn and Cu with the increasing yields. Optimized N supply achieved the highest yield and tended to increase grain concentrations of micronutrients compared to no or lower N supply. Excessive N supply did not result in any increases in yield or micronutrient nutrition for shoot or grain. These results indicate that optimized N management may be an economical method of improving micronutrient concentrations in maize grain with higher grain yield.</p></div

Dynamics of biomass (A), shoot Zn accumulation (B), shoot Fe accumulation (C), shoot Mn accumulation (D) and shoot Cu accumulation (E) of summer maize at V6 (six-leaf stage), V12 (12-leaf stage), R1 (silk emerging), R3 (milk stage) and R6 (physiological maturity) stages, respectively, with different N levels.

<p>The number of observations was shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093895#pone.0093895.s004" target="_blank">Table S2</a>.The bars represent the standard error of the mean. Bars with different lowercase letters are significantly different at different N levels (P<0.05).</p

Correlative coefficients (r) among the measured parameters at maturity (n = 149).

<p>Correlative coefficients (r) among the measured parameters at maturity (n = 149).</p

Dynamics of biomass (A), shoot Zn accumulation (B), shoot Fe accumulation (C), shoot Mn accumulation (D) and shoot Cu accumulation (E) of summer maize at V6 (six-leaf stage, n = 70), V12 (12-leaf stage, n = 54), R1 (silk emerging, n = 115), R3 (milk stage, n = 81) and R6 (physiological maturity, n = 149) stages, respectively.

<p>The bars represent the standard error of the mean.</p

Dynamics of shoot Zn concentration (A) shoot Fe concentration (B), shoot Mn concentration (C) and shoot Cu concentration (D) of summer maize at V6 (six-leaf stage), V12 (12-leaf stage), R1 (silk emerging), R3 (milk stage) and R6 (physiological maturity) stages, respectively, with different grain yield ranges.

<p>The number of observations was shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093895#pone.0093895.s004" target="_blank">Table S2</a>.The bars represent the standard error of the mean. Bars with different lowercase letters are significantly different at different yield ranges (P<0.05).</p

Dynamics of biomass (A), shoot Zn accumulation (B), shoot Fe accumulation (C), shoot Mn accumulation (D) and shoot Cu accumulation (E) of summer maize at V6 (six-leaf stage), V12 (12-leaf stage), R1 (silk emerging), R3 (milk stage) and R6 (physiological maturity) stages, respectively, with different yield ranges.

<p>The number of observations at each stage was shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093895#pone.0093895.s004" target="_blank">Table S2</a>. The bars represent the standard error of the mean. Bars with different lowercase letters are significantly different at different yield ranges (P<0.05).</p

Descriptive statistics of yield for total samples, four yield ranges (15.5% moisture), four different cultivars and four nitrogen (N) levels.

<p>Descriptive statistics of yield for total samples, four yield ranges (15.5% moisture), four different cultivars and four nitrogen (N) levels.</p

The Precambrian Khondalite Belt in the Daqingshan area, North China Craton: evidence for multiple metamorphic events in the Palaeoproterozoic era

<p>High-grade pelitic metasedimentary rocks (khondalites) are widely distributed in the northwestern part of the North China Craton and were named the ‘Khondalite Belt’. Prior to the application of zircon geochronology, a stratigraphic division of the supracrustal rocks into several groups was established using interpretative field geology. We report here SHRIMP U–Pb zircon ages and Hf-isotope data on metamorphosed sedimentary and magmatic rocks at Daqingshan, a typical area of the Khondalite Belt. The main conclusions are as follows: (1) The early Precambrian supracrustal rocks belong to three sequences: a 2.56–2.51 Ga supracrustal unit (the previous Sanggan ‘group’), a 2.51–2.45 Ga supracrustal unit (a portion of the previous upper Wulashan ‘group’) and a 2.0–1.95 Ga supracrustal unit (including the previous lower Wulashan ‘group’, a portion of original upper Wulashan ‘group’ and the original Meidaizhao ‘group’) the units thus do not represent a true stratigraphy; (2) Strong tectono-thermal events occurred during the late Neoarchaean to late Palaeoproterozoic, with four episodes recognized: 2.6–2.5, 2.45–2.37, 2.3–2.0 and 1.95–1.85 Ga, with the latest event being consistent with the assembly of the Palaeoproterozoic supercontinent Columbia; (3) During the late Neoarchaean to late Palaeoproterozoic (2.55–2.5, 2.37 and 2.06 Ga) juvenile, mantle-derived material was added to the crust. </p