Compositional variation of density and seismic velocities in natural peridotites at STP conditions: Implications for seismic imaging of compositional heterogeneities in the upper mantle
Compositional variation of density and seismic velocities in natural peridotites at STP conditions: Implications for seismic imaging of compositional heterogeneities in the upper mantle
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DOI：
10.1029/2003jb002413
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发表时间：
2003-09
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通讯作者：
Cin-Ty A. Lee
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文献类型：
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作者：
Cin-Ty A. Lee
[1]在标准温度（T）和压力（P）（STP）条件下，计算了Mg#（100 × Mg/（Mg + Fe））为86-94的固体天然尖晶石和石榴石橄榄岩样品（n = 133）的密度和弹性性质。这些物理性质被用来研究自然成分变化如何控制密度和地震速度。提供了一组相应的密度和地震速度的成分导数（d/dMg#）。因为对于橄榄岩矿物的不同组成端元，弹性模量的P和T导数非常相似，所以在STP条件下弹性模量随Mg#的变化在升高的P和T下保持。Mg#的增加导致VS的显著增加，因为矿物剪切模量对该参数敏感（dVS/dMg# = 0.0143 ± 0.0009 km s−1）。相比之下，纵波速度（VP）是不敏感的Mg#，而是，在STP条件下，与橄榄石丰度增加弱相关。因此，比值VP/VS与Mg#呈显著负相关（d（VP/VS）/dMg# = −0.00407 ± 0.00038）。因为VP/VS的温度依赖性与组成依赖性（1.7%/Mg#单位）相比很小（<0.04%/100 ℃），所以VP/VS的变化是组成变化的相当稳健的量度，即使温度变化。最后，一个新的密度与Mg#参数化。结合大量的岩石Mg#s的汇编橄榄岩包体从地幔的岩石圈地幔，它表明，地幔的内禀密度平衡到误差范围内的负热浮力所施加的较冷的热状态相对于上涌软流圈地幔。
[1] Densities and elastic properties of solid natural spinel- and garnet-peridotite samples (n = 133) at standard temperature (T) and pressure (P) (STP) conditions were calculated for compositions ranging from Mg# (100 × Mg/(Mg + Fe)) of 86–94. The physical properties were used to investigate how natural compositional variations control density and seismic velocity. A corresponding set of compositional derivatives (d/dMg#) of density and seismic velocity is provided. Because the P and T derivatives of elastic moduli are very similar for different compositional end-members of peridotitic minerals, the variation of elastic moduli with Mg# at STP conditions holds at elevated P and T. Increased Mg# leads to a significant increase in VS because of the sensitivity of mineral shear moduli to this parameter (dVS/dMg# = 0.0143 ± 0.0009 km s−1). In contrast, the compressional wave velocity (VP) is insensitive to Mg# and, instead, correlates weakly with increasing olivine abundance at STP conditions. The ratio VP/VS therefore exhibits a significant negative correlation with Mg# (d(VP/VS)/dMg# = −0.00407 ± 0.00038). Because the temperature dependency of VP/VS is small (<∼0.04%/100°C) compared to the compositional dependency (1.7%/Mg# unit), the variation in VP/VS is a fairly robust measure of compositional variation even when temperature varies. Finally, a new density versus Mg# parameterization is derived. Combined with a compilation of bulk-rock Mg#s of peridotite xenoliths from cratonic lithospheric mantle, it is shown that the intrinsic density of cratonic mantle balances to within error its negative thermal buoyancy imposed by its cooler thermal state relative to upwelling asthenospheric mantle.