...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Contributions to Mineralogy and Petrology >Ti-in-zircon thermometry: applications and limitations
【24h】

Ti-in-zircon thermometry: applications and limitations

机译：锆石钛测温法：应用和局限性

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The titanium concentrations of 484 zircons with U-Pb ages of approx 1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zir-cons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413-433) without making corrections for reduced oxide activities (e.g., TiO_2 or SiO_2), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500 deg to 850 deg C, and are lower than either zircon satu-ration temperatures (for granitic rocks) or predicted crys-tallization temperatures of evolved melts (approx 15 percent melt residue for mafic rocks). Temperatures average: 653 + -124 deg C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 + - 111 deg C (261 zircons) for mafic rocks, and 758 + - 98 deg C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced a_(TiO_2) or a_(SiO_2) variable pressure, deviations from Henry's Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystal-lization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with signifi-cantly lower crystallization temperature for the last 10-15 percent melt residue than that of the main rock. While some mag-matic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti content from core to rim, or correlation with zoning, age, U content, Th/U ratio, or concordance in U-Pb age. Thus, it is likely that other variables, in addition to temperature and a_(TiO_2) are important in controlling the Ti content of zircon. The Ti contents of igneous zircons from different rock types worldwide overlap significantly. However, on a more restricted regional scale, apparent Ti-in-zircon temperatures correlate with whole-rock SiO_2 and HfO_2 for plutonic rocks of the Sierra Nevada batholith, averaging 750 deg C at 50 wt.percent SiO_2 and 600 deg C at 75 wt. percent Among felsic plutons in the Sierra, peraluminous granites average 610 + - 8 deg C, while metaluminous rocks average 694 + - 94 deg C. Detrital zircons from the Jack Hills, Western Australia with ages from 4.4 to 4.0 Ga have apparent temperatures of 717 + - 108 deg C, which are intermediate between values for felsic rocks and those for mafic rocks. Although some mafic zircons have higher Ti content, values for Early Archean detrital zircons from a proposed granitic provenance are similar to zircons from many mafic rocks, including anorthosites from the Adirondack Mts (709 + - 76 deg C). Furthermore, the Jack Hills zircon apparent Ti-temperatures are significantly higher than measured values for peraluminous granites (610 + - 88 deg C). Thus the Ti concentration in detrital zircons and apparent Ti-in-zircon temperatures are not sufficient to independently identify parent melt composition.
机译：通过离子微探针测量了484个锆石的钛浓度，U-Pb年龄约为1 Ma至4.4 Ga。样品来自45种不同的火成岩（365个锆石）以及金伯利岩，早期太古宙碎屑锆石（32个）和锆石参考材料（3个）的锆石大晶体（84个）。选择了代表大范围火成岩成分的样品。大多数锆石含有少于20 ppm的钛。使用锆石中的钛温度计（Watson等人，2006，Contrib Mineral Petrol 151：413-433）计算出锆石结晶的表观温度，而未对降低的氧化物活性（例如TiO_2或SiO_2）或可变压力进行校正。锆石中钛的平均表观温度范围为500摄氏度至850摄氏度，低于锆石饱和温度（对于花岗岩）或预测的析出熔体结晶温度（镁铁矿约15％的熔渣） ）。平均温度：长英质至中火成岩为653 + -124摄氏度（2个标准差，60锆石），镁铁质岩石为758 +-111摄氏度（261锆石），而758 +-98摄氏度（84锆石）来自金伯利岩的地幔巨晶。单独地，减小的a_（TiO_2）或a_（SiO_2）可变压力，背离亨利定律的偏差以及亚固相线Ti交换的影响不足以解释火成岩中锆石晶体化看似较低的温度。 MELT的计算表明，镁铁质岩浆可以演化成含水熔体，其最后10-15％的熔体残余物的结晶温度明显低于主岩。虽然一定岩浆锆石肯定在这样的晚期含水熔体中形成，但在隐晶石或玻璃中包含的锆石中发现了较低的表观温度，这表明这些锆石并非来自残留的熔体。几乎所有被分析不止一次的锆石都观察到钛浓度的晶内变异性超出分析精度。但是，Ti含量从核到边缘没有系统的变化，也没有与分区，年龄，U含量，Th / U比或U-Pb年龄的一致性相关。因此，除了温度和α_（TiO_2）之外，其他变量可能对控制锆石的Ti含量也很重要。全球范围内不同岩石类型的火成锆石的Ti含量明显重叠。但是，在更局限的区域尺度上，内华达山脉岩溶岩生岩的表观锆石温度与全岩SiO_2和HfO_2相关，在SiO_2为50 wt％时平均为750℃，在75 wt％时为600℃。 。在塞拉山脉的长英质岩体中，高铝花岗岩平均为610 +-8摄氏度，而金属铝质岩石的平均为694 +-94摄氏度。西澳大利亚州杰克山的碎屑锆石的表观温度为4.4至4.0 Ga +-108摄氏度，介于长英质岩石和镁铁质岩石之间。尽管某些镁铁质锆石的Ti含量较高，但拟建花岗岩源的早太古宙碎屑锆石的值与许多镁铁质岩石中的锆石相似，包括来自阿迪朗达克山（Adirondack Mts）（709 +-76℃）的钙铁矿。此外，Jack Hills锆石的表观Ti温度明显高于高铝花岗岩的测量值（610 +-88摄氏度）。因此，碎屑锆石中的Ti浓度和锆石中Ti的明显温度不足以独立地确定母体熔体成分。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号