Widespread active detachment faulting and core complex formation near 13°N on the Mid-Atlantic Ridge

Author Posting. © Nature Publishing Group, 2006. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 442 (2006): 440-443, doi:10.1038/nature04950.Oceanic core complexes are massifs in which lower crustal and upper mantle rocks are exposed at the sea floor. They form at mid-ocean ridges through slip on detachment faults rooted below the spreading axis. To date, most studies of core complexes have been based on isolated inactive massifs that have spread away from ridge axes. A new survey of the Mid-Atlantic Ridge (MAR) near 13°N reveals a segment in which a number of linked detachment faults extend for 75 km along one flank of the spreading axis. The detachment faults are apparently all currently active and at various stages of development. A field of extinct core complexes extends away from the axis for at least 100 km. The new data document the topographic characteristics of actively-forming core complexes and their evolution from initiation within the axial valley floor to maturity and eventual inactivity. Within the surrounding region there is a strong correlation between detachment fault morphology at the ridge axis and high rates of hydroacoustically-recorded earthquake seismicity. Preliminary examination of seismicity and seafloor morphology farther north along the MAR suggests that active detachment faulting is occurring in many segments and that detachment faulting is more important in the generation of ocean crust at this slow-spreading ridge than previously suspected.This work was supported by the National Science Foundation

Pathomorphological Diagnosis of Splenic Diffuse Red Pulp Small B-Cell Lymphoma

Background. Unclassifiable splenic B-cell lymphoma/leukemia is a rare and poorly studied disorder introduced in the WHO classification of hematopoietic and lymphoid tissue malignancies for the first time in 2008. This type of lymphoma requires differential diagnosing between hairy cell leukemia-variant (HCL-V) and splenic diffuse red pulp small B-cell lymphoma (SDRPL). Aim. To develop criteria for diagnosis of SDRPL by comparison of bone marrow biopsies (BMB) and surgical specimens of the spleen. Methods. In the Department of Morbid Anatomy of the Hematology Research Center, preoperative BMBs and surgical specimens of the spleen (2013–2015) were compared in 71 patients (men/women ratio 1:2.6, age range 44–81, median age 58 years) using morphological and extended immunohistochemical studies. Sanger sequencing and PCR assay were carried out to analyze the mutational status of IgHV and to identify mutations in MAP2K1, NOTCH, BRAF. Results. SDRPL was diagnosed in 5 (7 %) of 71 patients. In 2 groups of patients (with normal and high WBC count), the morphological features of spleen tissue were similar to those of a neoplastic substrate of HCL-V. The immunohistochemical assay demonstrates monomorphic expression of CD20 and DBA.44 and heterogeneous expression of CD11c, TRAP, CD103, CD123 in all cases. In none of the 5 cases, expression of CD25, CD27, Cyclin D1, Annexin-1 was found. In bone marrow (unlike HCL and HCL-V), predominantly interstitial and intravascular scant CD20+ lymphoid infiltration (4 of 5 cases) was found without detectable nucleoli in nuclei of small lymphoid cells. In 1 case, there was a combined lymphoid infiltration: CD20+ microfocal-interstitial infiltration with an intravascular component. No persistent molecular mutations in the spleen tissue specimens were found. Conclusion. SDRPL is diagnosed in 7 % of splenic B-cell lymphomas. It is a rare disorder, whose verification requires an integrated approach taking into account clinical and laboratory data, results of flow cytometry, cytological, morphological, extended IHC and molecular biological studies