Global distribution of geothermal gradients in sedimentary basins

IF 8.9 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
Folarin Kolawole , Jonathan C. Evenick
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引用次数: 0

Abstract

The heat budget of sedimentary basins is determined by heat transfer across the lithosphere-asthenosphere boundary and lithospheric heat sources, such that the tectonic evolution of their host continental and oceanic lithosphere ultimately impact the present-day heat flow and average geothermal gradients. Recent increase in availability of publicly-accessible geothermal gradient measurements across the world provides an opportunity to globally assess the dominant controls on the thermal regime of sedimentary basins. Thus, we compile a global dataset of ∼ 152,000 unique data points with constrained bottomhole temperature measurements and assess the relationships between geothermal gradient and selected independent tectonic variables, including crustal and lithospheric thicknesses, crustal age, sediment thickness, and basin type. The results show that in both oceanic and continental settings, geothermal gradients exhibit a non-linear, systematic variation with the tectonic variables. We find that oceanic geothermal gradients decrease with increasing crustal age and lithospheric thickness. Geothermal gradients in the continents show no clear relationships with thermotectonic crustal age, but decrease with increasing crustal and lithospheric thicknesses. Gradients drop significantly at 1.5 km sediment-cover thickness, likely reflecting the effect of high sedimentation rates, but show a striking rise at > 12 km thicknesses, potentially influenced by thinned lithosphere and thermal blanketing effects. The commonly-assumed ‘normal’ gradient of 25 °C/km for continents is only valid for a narrow range (1.5–12.5 km) of sedimentary cover-thickness, and oceanic ‘normal’ gradient may be as high as 50–75 °C/km for > 20 Ma crustal age and > 50 km-thick lithosphere. We show that, conditionally, crustal age may best predict average geothermal gradients in oceanic settings, and lithosphere thickness in continents. Further, we observe that tectonic basin types exhibit distinct ranges of gradients that reflect their prevalent tectonic and geodynamic origins. Despite the complexities of determining shallow-crustal thermal conductivities, the results provide insights that fingerprint distinct tectonic settings based on the broad distribution of their geothermal gradients.

Abstract Image

沉积盆地地热梯度的全球分布
沉积盆地的热收支是由岩石圈-软流圈边界的热传递和岩石圈热源决定的,因此其所在大陆和海洋岩石圈的构造演化最终影响了现今的热流和平均地温梯度。最近,全球范围内可公开获得的地热梯度测量的可用性增加,为全球评估沉积盆地热状态的主要控制因素提供了机会。因此,我们编制了一个包含约152,000个独特数据点的全球数据集,其中包含有限的井底温度测量数据,并评估了地热梯度与选定的独立构造变量(包括地壳和岩石圈厚度、地壳年龄、沉积物厚度和盆地类型)之间的关系。结果表明,在大洋和大陆背景下,地温梯度随构造变量的变化均呈非线性系统变化。海洋地温梯度随地壳年龄和岩石圈厚度的增加而减小。大陆地温梯度与地壳热构造年龄关系不明显,随地壳和岩石圈厚度的增加而减小。梯度在1.5 km沉积物覆盖厚度处显著下降,可能反映了高沉积速率的影响,但在>厚度为12公里,可能受到岩石圈变薄和热覆盖效应的影响。通常假设的大陆25°C/km的“正常”梯度仅适用于沉积物覆盖厚度的狭窄范围(1.5-12.5 km),而海洋的“正常”梯度可能高达50-75°C/km。20 Ma地壳年龄和>50千米厚的岩石圈。我们表明,在有条件的情况下,地壳年龄可以最好地预测海洋环境中的平均地温梯度,以及大陆环境中的岩石圈厚度。此外,我们观察到构造盆地类型表现出不同的梯度范围,反映了其普遍的构造和地球动力学起源。尽管确定浅层地壳热导率很复杂,但结果提供了基于其地热梯度广泛分布的不同构造背景的见解。
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来源期刊
Geoscience frontiers
Geoscience frontiers Earth and Planetary Sciences-General Earth and Planetary Sciences
CiteScore
17.80
自引率
3.40%
发文量
147
审稿时长
35 days
期刊介绍: Geoscience Frontiers (GSF) is the Journal of China University of Geosciences (Beijing) and Peking University. It publishes peer-reviewed research articles and reviews in interdisciplinary fields of Earth and Planetary Sciences. GSF covers various research areas including petrology and geochemistry, lithospheric architecture and mantle dynamics, global tectonics, economic geology and fuel exploration, geophysics, stratigraphy and paleontology, environmental and engineering geology, astrogeology, and the nexus of resources-energy-emissions-climate under Sustainable Development Goals. The journal aims to bridge innovative, provocative, and challenging concepts and models in these fields, providing insights on correlations and evolution.
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