北海道大学 · 物理学・天文学
北川紀行教授の研究室は、隕石に含まれる原始的太陽系微粒子の化学組成と酸素同位体比を高精度な二次イオン質量分析法（SIMS）を用いて解析することで、太陽系初期の物質形成メカニズムを解明しています。特に、Ca-Al-富含礫石（CAI）の形成過程における酸素同位体の時間的変化や、外惑星的天体から返還された小惑星 Ryugu の母天体の環境を解明しています。これらの研究を通じて、太陽系内での物質移動や化学的変化のメカニズムを解明しています。
Figures are computed from collected data and may differ slightly.
TS34 is a Type B1 Ca-Al-rich inclusion (CAI) from the Allende CV3 chondrite, consisting of spinel, melilite, Ti-Al-rich clinopyroxene (fassaite) and minor anorthite in an igneous texture. Oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in TS34. Using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite, the oxygen isotopic
The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: <sup>16</sup>O-rich (associated with refractory inclusions) and <sup>16</sup>O-poor (associated with chondrul
Abstract– Different oxygen isotopic reservoirs have been recognized in the early solar system. Fluffy type A Ca‐Al‐rich inclusions (CAIs) are believed to be direct condensates from a solar nebular gas, and therefore, have acquired oxygen from the solar nebula. Oxygen isotopic and chemical compositions of melilite crystals in a type A CAI from Efremovka CV3 chondrite were measured to reveal the temporal variation in oxygen isotopic composition of surrounding nebular gas during CAI formation. The
Abstract Coarse‐grained, igneous Ca‐Al‐rich inclusions (CAIs) in CV chondrites formed through multiple melting events. We conducted in situ O‐isotope analysis and Al‐Mg systematics by secondary ion mass spectrometry of relict and overgrown minerals from a partial melting event in an Allende Type B CAI, Golfball. Golfball has a Type B CAI bulk composition and a unique structure: a fassaite‐rich mantle enclosing a melilite‐rich core. Many of the blocky melilite crystals in the core have irregularl
Abstract Al–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS) have revealed the initial 26 Al/ 27 Al ratios, ( 26 Al/ 27 Al) 0 , for individual Ca‐Al‐rich inclusions (CAIs) in meteorites. We find that the relative sensitivity factors of 27 Al/ 24 Mg ratio for SIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variations based on their chemical compositions. This underscores the critical need for using appropriate hibonite standards to obtain
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