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Shoboji Diorite Formation

Shoboji Diorite Fm

Period:

Cambrian

Age Interval:

latest Cambrian (Stage 10), (8a)

Province:
South Kitakami Belt-Okago region

Type Locality and Naming

Nagasaka-Soma district

Synonym:

Lithology and Thickness

It is composed of nearly massive diorite to gabbro, and not thought to have been overprinted by the Matsugadaira Motai high-pressure/low-temperature metamorphism.

[Figure 1: Stratigraphy of the Palaeozoic of the South Kitakatmi Belt, NE Japan (after M. Ehiro et al., 2016)]

Lithology Pattern:

Granitic

Relationships and Distribution

Lower contact

It is in fault contact with Motai metamorphic rocks. Regionally, the schematic strat column indicates the next older unit as Metamorphic Matsugadaira Unit Fm

Upper contact

It is in fault contact with the lower part of the Tobigamori Fm. Regionally, the schematic strat column indicates the next younger unit as Ainosawa Fm

Regional extent

Nagasaka-Soma district. The Shoboji Diorite is sporadically distributed as small bodies near and to the east of Shoboji, Nagasaka district.

GeoJSON

null

Fossils

Age

N-MORB normalized incompatible trace element patterns show that these plutonic rocks were derived from subduction zone magma (Kanisawa & Ehim 1997), with an intrusion age considered to be latest Ordovician (K-Ar hornblende ages: c. 440 Ma; Kanisawa & Ehim 1997) or latest Cambrian (U-Pb zircon age: 493 Ma; Isozaki et al., 2015).

Age Span:

Beginning stage:

Cambrian Stage 10

Fraction up in beginning stage:

0.0

Beginning date (Ma):

491.00

Ending stage:

Cambrian Stage 10

Fraction up in the ending stage:

1.0

Ending date (Ma):

486.85

Depositional setting

Depositional pattern:

Additional Information

Compiler:

Moreno, T., WALLIS, S., Kojima, T. & Gibbons, W. (Eds) 2016. The Geology of Japan. Geological Society. London. 1-24.