Multi‐anvil re‐equilibration experiments of a Dabie Shan ultrahigh‐pressure eclogite within the diamond‐stability fields
Multi‐anvil re‐equilibration experiments of a Dabie Shan ultrahigh‐pressure eclogite within the diamond‐stability fields
复制标题
DOI：
10.1046/j.1440-1738.1998.00179.x
复制
发表时间：
1998-04
期刊：
影响因子：
1.5
通讯作者：
K. Okamoto;S. Maruyama
中科院分区：
文献类型：
--
作者：
K. Okamoto;S. Maruyama
用大别山超高压地体中的榴辉岩(UHP303)和+1.1wt%K2O(UHK303)组成的榴辉岩(UHP303)，在P=2.6~3.2 GPaT=90 0~10 0 0°C，P=3~7 Gpa，T=90 0~12 0 0°C的条件下，用1000吨单轴多压头装置(∼-10 0 0)进行再平衡实验研究。UHP303的运行产物由石榴石、钠辉石、含或不含SiO_2相和多硅白云母组成。质构证据表明，UHP303的固相线在5 Gpa时位于900至1000℃之间，在3 GPa3和7 Gpa时高于1000℃。在UHK303中，固相线温度在3-5 GPa时降至1000℃，在5 GPa时降至900℃以下。测定了所有原料的成岩矿物组成，并与原料进行了比较。与原始石榴石(Grs16-26，ALM 21-26，Pyp 42-61)相比，所有原料的石榴石具有相对较高的铝榴石+石榴石组分(Alm+Sps24-30摩尔%)和较低的粗面组分(12-16)和恒定的镁铝榴石组分(58-61)。在P=3-7 Gpa压力范围内，当温度高于900℃时，稳定的钙钠辉石为钠辉石而不是绿辉石，且CPX的组成间隙完全闭合。Ca-Na辉石的K2O含量是P和T的函数，是钻石稳定性领域的潜在晴雨表。石榴石中的钠含量可以忽略不计。利用所提出的钙钠辉石中K2O含量作为压力的函数，建议在T=900°C时Kokchetav超高压条件的最大值为7 Gpa。
An eclogite (UHP303) formed at ∼ 700 °C and P > 4 GPa from the Dabie Shan ultrahigh‐pressure (UHP) terrane and the same sample + 1.1 wt% K2O (UHK303) were used for re‐equilibrium experimental studies at P = 2.6–3.2 GPa and T = 900–1000 °C, employing a piston cylinder apparatus, and at P = 3–7 GPa and T = 900–1200 °C, employing a 1000 ton uniaxial multi‐anvil apparatus (SPI‐1000). Run products of UHP303 are composed of garnet, sodic augite, with or without a SiO2 phase and phengite. Textural evidence indicates that the solidus lies between 900 and 1000 °C at 5 GPa, and above 1000 °C at 3 and 7 GPa for UHP303. The solidus temperature decreases to 1000 °C at 3–5 GPa and below 900 °C at 5 GPa in UHK303. Composition of rock‐forming minerals of all run products were determined and compared with those of starting materials. Garnets of all run products have a relatively higher almandine + spessartine component (alm + sps 24–30 mol%) and lower grossular component (12–16) with constant pyrope component (58–61), compared to the starting garnet (grs16–26, alm 21–26, pyp 42–61). The stable Ca–Na pyroxenes are sodic augite rather than omphacite at T higher than 900 °C in the P = 3–7 GPa pressure range, and the Cpx compositional gap is completely closed. The K2O content of Ca–Na pyroxenes is a function of P and T, and serves as a potential barometer in the diamond‐stability field. Sodium content in garnet is negligible. Using the proposed K2O content in Ca–Na pyroxene as a function of pressure, the maximum Kokchetav UHP condition is suggested to have been 7 GPa at T = 900 °C.