記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Current Science Association  

DOI： 10.18520/cs/v121/i7/906-911

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Extensional and compressional structures are globally abundant on Mars. Distribution of these structures and their ages constrain the crustal stress state and tectonic evolution of the planet. Here in this paper, we report on our investigation over the distribution of the tectonic structures and timings of the associated stress fields from the Noachis-Sabaea region. Thereafter, we hypothesize possible origins in relation to the internal/external processes through detailed morphostructural mapping. In doing so, we have extracted the absolute model ages of these linear tectonic structures using crater size-frequency distribution measurements, buffered crater counting in particular. The estimated ages indicate that the tectonic structures are younger than the mega impacts events (especially Hellas) and instead they reveal two dominant phases of interior dynamics prevailing on the southern highlands, firstly the extensional phase terminating around 3.8 Ga forming grabens and then compressional phase around 3.5–3.6 Ga producing wrinkle ridges and lobate scarps. These derived absolute model ages of the grabens exhibit the age ca. 100 Ma younger than the previously documented end of the global extensional phase. The following compressional activity corresponds to the peak of global contraction period in Early Hesperian. Therefore, we conclude that the planet wide heat loss mechanism, involving crustal stretching coupled with gravitationally driven relaxation (i.e., lithospheric mobility) resulted in the extensional structures around Late Noachian (around 3.8 Ga). Lately cooling related global contraction generated compressional stress ensuing shortening of the upper crust of the southern highlands at the Early Hesperian period (around 3.5–3.6 Ga).

DOI： 10.1016/j.gsf.2018.05.016

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Southern highlands of Mars have experienced regional to global scale deformations in the history of its evolution. Deformational structures originated from impact-induced stresses and later viscous relaxation of the impact basin to cooling related global contraction. Here in this study, we investigated an Early Hesperian (Eo-Archean / Paleo-Archean equivalent to the Earth) aged lobate scarp i.e., surface signature of thrust fault, possibly originated because of global contraction. We used ‘offset crater perimeter’ measurement technique using high-resolution data (both image and DTM) to execute most precise estimation of fault plane slope and length–displacement relationship. The derived range of fault plane slope is much narrower (21°–29°) than the previously cited 20° to 35° range. Displacement–length ratio (4.51 × 10−3) is also unique and lower than the previously evaluated values of lobate scarps from other region (mainly from dichotomy boundary) of Mars. The newly derived results from the morphometric analysis are due the differential stress pattern and the distinct basement rock rheology. Our results highlight the need for more high-resolution estimation of lobate scarps from several regions with the methodology employed in this study to better understand the global Martian early tectonic scenario.

DOI： 10.1016/j.jsg.2018.04.018

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）  

The Noachis-Sabaea region in the southern highlands preserves some of the oldest Martian crust. It records deformation by both endogenic and exogenic processes. This deformation includes giant impacts and their impact stresses, which could have resulted in both the reactivation and modification of pre-impact tectonic structures, in addition to impactgenerated tectonic structures. There are also widespread extensional and compressional tectonic structures, which were formed due to endogenic processes. We have produced the first detailed morphostructural map of the Noachis-Sabaea region, which details the characteristics and spatial arrangements of structures in the region, forms the basis for making inferences about Noachian-Hesperian crustal activity, and provides information for further studies regarding the reconstruction of the evolutional history of the region.

DOI： 10.1080/17445647.2017.1379913

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Partial melting in the middle to lower crustal level produces melts of granitic composition during orogeny. Thrusts play a vital role in their exhumation after consolidation of these granitic melts. In this paper we focus on one such granite along the eastern margin of the Delhi Fold Belt (DFB) rocks near Srinagar, Rajasthan, India. This is the first report of granite within the area and holds a key stratigraphic position in the entire rock package. The said granite is found to be intrusive to the DFB metasediments as well as their basement popularly known as the Banded Gneissic Complex (BGC). We disentangle the deformation fabrics seen within the granite and associated DFB metasediments, suggesting that subsequent to emplacement and consolidation, the granite has co-folded along with the country rocks. Three deformational events could be identified within the DFB metasediments namely, D1D, D2D and D3D. The peak metamorphism was achieved in the D1D event. The granite magma is generated and emplaced late syn-kinematic to D1D and thereafter is deformed by D2D and D3D producing D1G and D2G structural fabrics. These compressive deformations resulted in the collapse of the basin; the combined package of DFB rocks and the granite was thrusted eastwards over the basement rocks. The tectonic transport direction during thrusting is suggested eastwards from our structural analysis. Transverse faults developed perpendicular to the length of the granite have led to partitioning of the strain thereby showing a heterogeneity in the development of fabric within it.

DOI： 10.1007/s12040-014-0461-9

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