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Local inversion of magnetic anomalies: Implication for Mars' crustal evolution

机译：磁异常的局部反演：对火星地壳演化的启示

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Martian magnetic anomalies have been revealed by the Mars Global Surveyor (MGS) mission in the south hemisphere of Mars. The present study models anomalies located in the ancient Terra Sirenum area between latitudes 26°S and 40°S and longitudes 185°E and 210°E using forward and inverse approaches. While the high-altitude measurements reveal the presence of two main magnetic anomalies, three are detected by low-altitude data. They are modeled as uncorrelated dipolar sources. Forward models predict large magnetizations between 30 and 60 A/m. A generalized non-linear inversion is used to determine the characteristics of the dipoles, based on different subsets of data. Low-altitude measurements inversion leads to more reliable results than those obtained by the inversion of high-altitude measurements only. Inversion of both low- and high-altitude data together provides with three dipoles that explain more than 57% of the signal, within this 10~6km~2 area. All dipoles have large magnetizations. Serpentinization of the early martian crust can explain such remanent magnetizations. Two resulting dipoles are 56 km deep, which suggests a locally thick martian crust. The last one is shallower (31km). This indicates different origins and/or magnetization processes. Paleomagnetic poles are calculated and located around the Tharsis bulge. It suggests that Tharsis formed at high latitudes and moved toward its present location by polar reorientation.
机译：火星南半球的火星全球测量师（MGS）任务揭示了火星的磁异常。本研究使用正向和逆向方法模拟了位于古代Terra Sirenum地区介于纬度26°S和40°S和经度185°E和210°E之间的异常。虽然高空测量显示存在两个主要的磁异常，但低空数据可检测到三个。它们被建模为不相关的偶极子源。正向模型预测磁化强度在30至60 A / m之间。基于数据的不同子集，可以使用广义非线性反演来确定偶极子的特性。与仅通过高空测量反演获得的结果相比，低空测量反演可获得更可靠的结果。在这10〜6km〜2范围内，低海拔和高海拔数据的反演共同提供了三个偶极子，可解释超过57％的信号。所有偶极子都有很大的磁化强度。早期火星地壳的蛇形化可以解释这种剩余的磁化强度。由此产生的两个偶极子的深度为56 km，这表明它是一个局部较厚的火星地壳。最后一个更浅（31公里）。这表明不同的起源和/或磁化过程。计算了古磁极，并将其定位在Tharsis凸起周围。这表明塔里西斯形成于高纬度，并通过极地重新定向向其当前位置移动。

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