On the rise: using reentrants to extract magma ascent rates in the Bandelier Tuff caldera complex, New Mexico, USA
On the rise: using reentrants to extract magma ascent rates in the Bandelier Tuff caldera complex, New Mexico, USA
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上升趋势：利用重入体提取美国新墨西哥州班德利尔凝灰岩火山口复合体的岩浆上升速率
DOI：
10.1007/s00445-021-01518-4
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发表时间：
2022
影响因子：
3.5
通讯作者：
Waelkens, C. M.
中科院分区：
文献类型：
--
作者：
Saalfeld, Megan A.;Myers, M. L.;deGraffenried, R.;Shea, T.;Waelkens, C. M.
班德利耶凝灰岩是随后两次类似体积和成分的火山口形成喷发的结果，这两次喷发产生了奥托伊(1.61 Ma)和齐雷格(1.26 Ma)成员。它们非常相似的特征和共同的火山口边界为研究岩浆上升是否受到先前存在的火山口边界的影响提供了一个独特的平台。在这里，我们通过模拟石英主重入岩(未封闭的熔融包裹体)中的挥发分梯度(H2O，CO2缺失)，给出了每个成员初始柱状相内离散层的减压速率。对于下单元(n= 4/9)和上单元(n= 11/13)，成功的最佳拟合一维扩散模型得到的平均减压速率分别为0.041 Mpa/S和0.026 Mpa/S。从两次喷发中提取的速率之间的强烈重叠表明，上升动力没有显著变化。然而，较老的Oowi成员包含大量无法充分建模的折返者，这意味着一条比我们不断解压方法可以重建的路径更复杂。相比之下，来自Tshirege的再入者可以很容易地从存储深度进行建模，这一观察表明，在第二次喷发中，管道形成更有效。为了进一步评估这些提取速率的稳健性，我们随后应用了2D扩散模型，该模型考虑了各种折返几何；令人惊讶的是，我们发现1D派生的速率几乎没有变化。相比之下，纳入班德利温度(~ 130°C)的不确定度会使速率变化340%-440%。然而，我们认为，从重入岩中提取的减压速率的最大差异来源是保存在每个秋季沉积中的极端范围，每个范围跨越三个数量级，表明极端的管道动态变化，并强调基于岩石学的上升速率可能变化很大，即使在单一取样层内也是如此。最后，在测量的剖面中没有检测到的二氧化碳浓度与在密封的熔体包裹体中检测到的数量(<； 200ppm)不一致，这一观察结果在其他硅系统(例如，美国毕晓普、新西兰奥鲁阿努伊、格拉斯哥圣托里尼)中也有发现。我们提出了两种机制来在喷发前从系统中去除CO2：(1)额外的结晶驱动CO2在上升之前进入流体相；或(2)由于初始喷发前压力的小下降而重入到无CO2的环境。这两种情况对岩浆体喷发前的状态都有重要的影响。
The Bandelier Tuff is the result of two subsequent caldera-forming eruptions of similar volume and composition which produced the Otowi (1.61 Ma) and Tshirege (1.26 Ma) members. Their remarkably similar characteristics and shared caldera boundaries provides a unique platform to investigate whether magma ascent is affected by the presence of a preexisting caldera boundary. Here, we present decompression rates for discrete layers within the initial plinian phase of each member by modeling volatile gradients (H2O, CO2absent) in quartz-hosted reentrants (unsealed melt inclusions). Successful best-fit 1D diffusion models for the lower (n= 4/9) and upper (n= 11/13) units resulted in average decompression rates of 0.041 MPa/s and 0.026 MPa/s, respectively. Strong overlap between rates extracted from the two eruptions suggests there was no significant change in ascent dynamics. However, the older Otowi member contains a larger number of reentrants that cannot be modeled adequately, suggesting a more complicated path than can be reconstructed with our constant decompression approach. In contrast, reentrants from the Tshirege can be readily modeled from storage depths, an observation that suggests conduit formation was more efficient in the second eruption. To further evaluate the robustness of these extracted rates, we then applied a 2D diffusion model, which considers various reentrant geometries; surprisingly, we find little alteration to 1D-derived rates. By contrast, incorporating the uncertainty in Bandelier temperature (~ 130 °C) shifts rates by 340–440%. However, we argue that the largest source of variation from decompression rates extracted from reentrants lies in the extreme range preserved within each fall deposit, each spanning three orders of magnitude, suggesting extreme conduit dynamic shifts, and emphasizing that petrologic-based ascent rates may vary widely, even within a single-sampled layer. Finally, the lack of detectable CO2concentrations in measured profiles is at odds with the amounts detected in sealed melt inclusions (< 200 ppm), an observation that has been made in other silicic systems (e.g., Bishop, USA; Oruanui, NZ; Santorini, GR). We propose two mechanisms to remove CO2from the system prior to eruption: (1) additional crystallization drove CO2into the fluid phase prior to ascent or (2) reentrants reset to a CO2free environment due to a small, initial pre-eruptive pressure decrease. Both scenarios have important implications for the pre-eruptive state of the magma body.
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影响因子：
3.5
作者：
Ferguson, David J.;Gonnermann, Helge M.;Swanson, Donald A.
通讯作者：
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影响因子：
5.3
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影响因子：
2.9
作者：
F. Goff;R. Warren;C. Goff;N. Dunbar
通讯作者：
N. Dunbar
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DOI：
--
发表时间：
1997
期刊：
影响因子：
--
作者：
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通讯作者：
Zhengjiu Xu
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DOI：
--
发表时间：
1978
期刊：
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作者：
B. Crowe;G. Linn;G. Heiken;M. Bevier
通讯作者：
M. Bevier